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diff --git a/systems/doc/metapost/source-manual/mpman.tex b/systems/doc/metapost/source-manual/mpman.tex new file mode 100644 index 0000000000..ec77468753 --- /dev/null +++ b/systems/doc/metapost/source-manual/mpman.tex @@ -0,0 +1,6008 @@ +% $Id: mpman.tex 2139 2018-02-19 14:38:47Z luigi.scarso@gmail.com $ +% MetaPost manual, by John Hobby. License at end. +\listfiles +\RequirePackage{ifpdf} +\ifpdf +\ifnum\pdftexversion<140 +\else +\pdfminorversion=5 +\pdfobjcompresslevel=1% Use compressed object streams. +\fi +\RequirePackage{cmap} +\fi +\documentclass{article} % article is NOT the original style +\usepackage[nofancy]{svninfo}% Access VCS information. +\svnInfo $Id: mpman.tex 2140 2019-06-01 14:38:47Z luigi.scarso@gmail.com $ +%\svnInfo $Id: mpman.tex 2139 2018-02-19 14:38:47Z luigi.scarso@gmail.com $ +\newcommand*{\mpversion}{2.00} + +\usepackage[T1]{fontenc} +\usepackage{lmodern} +\usepackage{textcomp} +\usepackage{mflogo} +\usepackage{makeidx} +\usepackage{fancyvrb} +\usepackage{ctabbing} +\RecustomVerbatimEnvironment + {verbatim}{BVerbatim}{baseline=c} +\usepackage{graphicx} +\usepackage[latin1]{inputenc} +\usepackage[textwidth=6in,textheight=8.65in]{geometry} +\usepackage{tocloft} + \setlength\cftbeforesecskip{1.3ex plus 0.3ex minus 0.3ex} + \setcounter{tocdepth}{2} +\usepackage{ltxtable} + + +\def\ttindex#1{{\tt #1}\index{#1?\texttt{#1}}} +\def\ttt{\texttt} % I get tired of typing this out + +\def\ConTeXt{Con\TeX t} + +\newcommand\descr[1]{{\langle\hbox{#1}\rangle}} +\newcommand\invisgap{\nobreak\hskip0pt\relax} +\newcommand\tdescr[1]{{\normalfont$\langle$\invisgap#1\invisgap$\rangle$}} + +\newcommand\pl{\dag} + +\newcommand\mathcenter[1]{\vcenter{\hbox{#1}}} + + +\renewcommand{\topfraction}{.85} +\renewcommand{\bottomfraction}{.7} +\renewcommand{\textfraction}{.15} +\renewcommand{\floatpagefraction}{.5} +\renewcommand{\dbltopfraction}{.66} +\renewcommand{\dblfloatpagefraction}{.66} +\setcounter{topnumber}{9} +\setcounter{bottomnumber}{9} +\setcounter{totalnumber}{20} +\setcounter{dbltopnumber}{9} + +\makeindex + +\usepackage{multicol} +\usepackage[rgb,x11names]{xcolor}% Optimize for screen reading. +\usepackage{hyperxmp} +\usepackage{hyperref} +\hypersetup{ + pdftitle={MetaPost: A User's Manual}, + pdfauthor={John D. Hobby and the MetaPost development team}, + pdfkeywords={MetaPost, PostScript, SVG, PNG, vector graphics language, + MetaFont, TeX} +} +\hypersetup{ + pdfstartview={XYZ null null null},% Zoom factor is determined by viewer. + colorlinks, + linkcolor=RoyalBlue3, + urlcolor=Chocolate4, + citecolor=SpringGreen3 +} +\usepackage[all]{hypcap} +\ifpdf +\pdfmapfile{=cm2lm.map}% replace CM by LM in figures +\else +\DeclareGraphicsExtensions{.mps} +\DeclareGraphicsRule{mps}{eps}{*}{} +\usepackage{breakurl} +\fi +\begin{document} +\VerbatimFootnotes +%%% Title page layout documentation is missing. +\begin{titlepage} + \vbox to \textheight {% + \vskip0pt + \vfil + \vfil + \vfil + \centerline{\resizebox{3.5in}{!}{\fontseries{b}\selectfont\MP}} + \vskip10bp% actually 21bp (-11bp) + \centerline{\includegraphics{mpman-60.mps}} + \vskip15bp% actually 21bp (-6bp) + \centerline{% + \resizebox{3.5in}{!}{% + \scshape% + \fontsize{28bp}{28bp}\selectfont + \strut\lowercase{A USER\kern-2bp\lower3bp\hbox{'}S MANUAL}% + }% + } + \vskip-11bp + \vfil + \vfil + \centerline{\large John D. Hobby} + \vskip3bp + \centerline{and the MetaPost development team} + \vskip20.8bp% actually 31.8bp (-11bp) + \centerline{\large documented version: \mpversion} + \vskip3bp +\tracingall \centerline{\svnInfoMaxToday} \tracingnone + \vskip\baselineskip + \centerline{Web page: {\tt https://tug.org/metapost}} + \centerline{Mailing list: {\tt https://lists.tug.org/metapost}} + \vfil + \vfil + } +\end{titlepage} + +\setlength{\columnsep}{2.5em} +\begin{multicols}{2} +\tableofcontents +\end{multicols} + +\section{Introduction} +\label{intro} + +MetaPost is a programming language much like Knuth's \MF\footnote{\MF\ +is a trademark of Addison Wesley Publishing +company.}\index{metafont?\MF}~\cite{kn:c} except that it outputs +either vector graphics in the Postscript or SVG formats or bitmap +graphics in the PNG format. Borrowed from \MF\ are the basic tools for +creating and manipulating pictures. These include numbers, coordinate +pairs, cubic splines, affine transformations, text strings, and boolean +quantities. Additional features facilitate integrating text and +graphics and accessing special features of +PostScript\footnote{PostScript is a trademark of Adobe Systems +Inc.}\index{PostScript} such as clipping, shading, and dashed lines. +Another feature borrowed from \MF\ is the ability to solve linear +equations that are given implicitly, thus allowing many programs to be +written in a largely declarative style. By building complex operations +from simpler ones, MetaPost achieves both power and flexibility. + +MetaPost is particularly well-suited to generating figures for technical +documents where some aspects of a picture may be controlled by +mathematical or geometrical constraints that are best expressed +symbolically. In other words, MetaPost is not meant to take the place +of a freehand drawing tool or even an interactive graphics editor. It +is really a programming language for generating graphics, especially +figures for \TeX\footnote{\TeX\ is a trademark of the American +Mathematical Society.}\index{TeX?\TeX} and troff\index{troff} documents. + +This document introduces the MetaPost language, beginning with the +features that are easiest to use and most important for simple +applications. The first few sections describe the language as it +appears to the novice user with key parameters at their default values. +Some features described in these sections are part of a predefined macro +package called Plain. Later sections summarize the complete language +and distinguish between primitives and preloaded macros from the Plain +macro package\index{Plain macros}. Reading the manual and creating +moderately complex graphics with MetaPost does not require knowledge of +\MF\ or access to {\sl The \MF book} \cite{kn:c}. However, to really +master MetaPost, both are beneficial, since the MetaPost language is +based on Knuth's \MF\ to a large extent. Appendix~\ref{MPvsMF} gives a +detailed comparison of MetaPost and \MF. + +The basic MetaPost documentation is completed with ``Drawing Boxes with +MetaPost'' and ``Drawing Graphs with MetaPost''---the manuals of the +\texttt{boxes} and \texttt{graph} packages originally developed by +John~D. Hobby. + +The MetaPost home page is \url{https://tug.org/metapost}. It has links +to much additional information, including many articles that have been +written about MetaPost. For general help and discussion, try the +\url{metapost@tug.org} mailing list; you can subscribe to this list at +\url{https://lists.tug.org/metapost}. + +The development repository is currently hosted at +\url{https://serveur-svn.lri.fr/svn/modhel/metapost}; web browsing and +anonymous svn checkout are allowed with username \texttt{anonsvn} and +password \texttt{anonsvn}. + +If bug reports get no reply from \url{metapost@tug.org}, feel free to +resend to \url{mp-implementors@tug.org}. (Please do not send reports +directly to Dr.~Hobby in any event.) + + +\section{Basic Drawing Statements} +\label{basic} + +The simplest drawing statement is the one that draws a single dot with +the current pen at a given coordinate: +$$ +\begin{verbatim} +drawdot (30,0) +\end{verbatim} +\index{drawdot?\texttt{drawdot}} +\label{Ddrawdot} +$$ + +MetaPost can also draw straight lines. +Thus\index{draw?\texttt{draw}}\index{-{}-?\texttt{-{}-}} +$$ \hbox{\verb|draw (20,20)--(0,0)|} $$ +draws\index{draw?\texttt{draw}} a diagonal line and +$$ \hbox{\verb|draw (20,20)--(0,0)--(0,30)--(30,0)--(0,0)|} $$ +draws a polygonal line like this: +$$ \includegraphics{mpman-1.mps} $$ + +What is meant by coordinates like \verb|(30,0)|? MetaPost uses the same +default coordinate system that PostScript\index{PostScript!coordinate +system} does. This +means that \verb|(30,0)| is 30 units to the right of the origin, where a +unit is $1\over72$ of an inch. We shall refer to this default unit as a +{\sl PostScript point\/}\index{PostScript!point}\index{point!PostScript} +to distinguish it from the standard printer's +point\index{point!printer's} which is $1\over72.27$ inches. + +MetaPost uses the same names for units of measure that \TeX\ and \MF\ +do. Thus +\verb|bp|\index{bp?\texttt{bp}}\index{units!bp?\texttt{bp}}\label{Dbp} +refers to PostScript points (``big points'') and +\verb|pt|\index{pt?\texttt{pt}}\index{units!pt?\texttt{pt}}\label{Dpt} +refers to printer's points. Other units of measure include +\verb|in|\index{in?\texttt{in}}\index{units!in?\texttt{in}}\label{Din} +for inches, +\verb|pc|\index{pc?\texttt{pc}}\index{units!pc?\texttt{pc}}\label{Dpc} +for picas, +\verb|cm|\index{cm?\texttt{cm}}\index{units!cm?\texttt{cm}}\label{Dcm} +for centimeters, +\verb|mm|\index{mm?\texttt{mm}}\index{units!mm?\texttt{mm}}\label{Dmm} +for millimeters, +\verb|cc|\index{cc?\texttt{cc}}\index{units!cc?\texttt{cc}}\label{Dcc} +for ciceros, and +\verb|dd|\index{dd?\texttt{dd}}\index{units!dd?\texttt{dd}}\label{Ddd} +for Didot points. For example, +$$ \hbox{\verb|(2cm,2cm)--(0,0)--(0,3cm)--(3cm,0)--(0,0)|} $$ +generates a larger version of the above diagram. It is OK to say +\verb|0| instead \verb|0cm| because {\tt cm} is really just a conversion +factor and {\tt 0cm} just multiplies the conversion factor by zero. +(MetaPost understands constructions like {\tt 2cm}\index{multiplication, + implicit} as shorthand for \verb|2*cm|). The coordinate \verb|(0,0)| +can also be referred to as +\texttt{origin}\index{origin?\texttt{origin}}\label{Dorigin}, as in +$$ \hbox{\verb|drawdot origin|} $$ + +It is convenient to introduce your own scale factor, say $u$. Then you +can define coordinates in terms of $u$ and decide later whether you want +to begin with \verb|u=1cm| or \verb|u=0.5cm|. This gives you control +over what gets scaled and what does not so that changing $u$ will not +affect features such as line widths. + +There are many ways to affect the appearance of a line besides just +changing its width, so the width-control mechanisms allow a lot of +generality that we do not need yet. This leads to the strange looking +statement\index{pickup?\texttt{pickup}}\index{pencircle?\texttt{pencircle}}% +\index{scaled?\texttt{scaled}} +$$ \hbox{\verb|pickup pencircle scaled 4pt|} $$ +for setting the line width (actually the pen size) for subsequent +\verb|draw| or \verb|drawdot| statements to 4 points. (This is about +eight times the default pen size). + +With such a large pen size, the \verb|drawdot| statement draws rather +bold dots. We can use this to make a grid of dots by nesting +\verb|drawdot| in a pair of loops:\index{loops}% +$$ +\begin{verbatim} +for i=0 upto 2: + for j=0 upto 2: drawdot (i*u,j*u); endfor +endfor +\end{verbatim} +\index{for?\texttt{for}} +\index{endfor?\texttt{endfor}} +$$ +The outer loop runs for $i=0,1,2$ and the inner loop runs for $j=0,1,2$. +The result is a three-by-three grid of bold dots as shown in Figure~\ref{fig1}. +The figure also includes a larger version of the polygonal line diagram that we +saw before. + +\begin{figure}[htp] +$$ \begin{verbatim} +beginfig(2); +u=1cm; +draw (2u,2u)--(0,0)--(0,3u)--(3u,0)--(0,0); +pickup pencircle scaled 4pt; +for i=0 upto 2: + for j=0 upto 2: drawdot (i*u,j*u); endfor +endfor +endfig; +\end{verbatim} +\quad \mathcenter{\includegraphics{mpman-2.mps}} +$$ +\caption{MetaPost commands and the resulting output} +\label{fig1} +\end{figure} + + +\section{The MetaPost Workflow} +\label{workflow} + +Before describing the MetaPost language in detail, let's have a look at +MetaPost's graphic design workflow. This section also contains a few +technical details about MetaPost's compilation process, just enough to +get you started. Section~\ref{workflow2} is more elaborate on this +topic. + +In this manual, we'll assume a stand-alone command-line executable of +the MetaPost compiler is used, which is usually called +\texttt{mpost}\index{mpost?\texttt{mpost}}. The syntax and program name +itself are system-dependent; sometimes it is named \texttt{mp}. The +executable is actually a small wrapper program around +\emph{mplib}\index{mplib?\emph{mplib}}, a library containing the +MetaPost compiler. The library can as well be embedded into third-party +applications.\footnote{C~API\index{mplib?\emph{mplib}!C~API} and Lua + bindings\index{mplib?\emph{mplib}!Lua bindings} are described in file + \verb|manual/mplibapi.pdf|\index{mplib?\emph{mplib}!mplibapi.pdf?\texttt{mplibapi.pdf}} + as part of the MetaPost distribution.} Section~\ref{mpimport} has +some brief information on how to use the MetaPost compiler built-into +Lua\TeX. For more information, please refer to the documentation of the +embedding application. + +The basic MetaPost workflow\index{workflow} is depicted in +figure~\ref{fig:mpworkflow}. Being a graphics description language, +creating graphics with MetaPost follows the +\emph{edit-compile-debug}\index{edit}\index{compile}\index{debug} +paradigm known from other programming languages. + +\begin{figure}[tbp] +$$ \includegraphics{mpman-charts-2.mps} $$ +\caption{The basic MetaPost workflow} +\label{fig:mpworkflow} +\end{figure} + +To create graphics with MetaPost, you prepare\index{edit} a text file +containing code in the MetaPost language and then invoke the +compiler\index{compile}, usually by giving a command of the form +$$ +\begin{verbatim}[commandchars=\\\{\}] +mpost \tdescr{input file} +\end{verbatim} +\index{mpost?\texttt{mpost}} +$$ +on the command-line. MetaPost input files\index{files!input} normally +have names ending \texttt{.mp}\index{mp file?{\tt mp} + file}\index{files!mp?{\tt mp}} but this part of the name can be +omitted when invoking MetaPost. A complete description of the +command-line syntax can be found in Section~\ref{refman:commandline}. + +Any terminal I/O during the compilation process is summarized in a +transcript\index{files!transcript}\index{transcript file|see{files, + transcript}} file called \texttt{\tdescr{jobname}.log}\index{log + file?{\tt log} file}\index{files!log?{\tt log}}, where +\tdescr{jobname} is the base name of the input file. This includes +error messages and any MetaPost commands entered in interactive mode. + +If all goes well during compilation, MetaPost outputs one or more +graphic files in a variant of the PostScript format, by default. +PostScript output can be previewed\index{preview} with any decent +PostScript viewer, e.g., GSview\index{GSview} or +PS\_View\index{PSView?PS\_View}. Section~\ref{preview} has some tips +and discusses several more elaborate ways for previewing PostScript +output. Particularly, if graphics contain text labels, some more work +might be required to get robust results in a PostScript viewer. +MetaPost is also capable of generating graphics in the SVG\index{SVG} +and PNG\index{PNG} formats. These file types can be previewed with +certain web browsers, for example Firefox~3\index{Firefox} or +Konqueror~4.2\index{Konqueror}, or general purpose image viewers. + +What does one do with all the graphic files? PostScript files are +perfectly suitable for inclusion into documents created by +\TeX\index{TeX?\TeX} or troff\index{troff}. The SVG format, as an XML +descendant (Extensible Meta Language), is more aiming at automated data +processing/interchanging. The PNG format is a losslessly compressing +bitmap format. Both, SVG and PNG graphics, are widely used for web +applications. Section~\ref{mpimport} deals with the import of MetaPost +graphics into external applications. + +A MetaPost input file\index{files!input}\index{edit}\index{edit} +normally contains a sequence of +\verb|beginfig()|\index{beginfig?\texttt{beginfig}}, +\verb|endfig|\index{endfig?\texttt{endfig}} pairs with an +\verb|end|\index{end?\texttt{end}} statement after the last +one.\footnote{Omitting the final \verb|end| statement causes MetaPost to + enter interactive mode\index{interactive mode} after processing the + input file.} These are macros that perform various administrative +functions and ensure that the results of all drawing operations get +packaged up and translated into PostScript (or the SVG or PNG format). +The numeric argument to the \verb|beginfig| macro determines the name of +the corresponding output file, whose name, by default, is of the form +\texttt{\tdescr{jobname}.\tdescr{n}}, where \tdescr{n} is the current +argument to \verb|beginfig| rounded to the nearest integer. As an +example, if a file is named \texttt{fig.mp} and contains the lines +$$ +\begin{verbatim}[commandchars=\\\{\}] +beginfig(1); + \tdescr{drawing statements} +endfig; +end +\end{verbatim} +$$ +the output from statements between \verb|beginfig(1)| and the next +\verb|endfig| is written in a file \texttt{fig.1}\index{files!output}. + +Statements can also appear outside \verb|beginfig| \ldots\ +\verb|endfig|. Such statements are processed, but drawing operations +generate no visible output. Typically, global configurations are put +outside \verb|beginfig| \ldots\ \verb|endfig|, e.g., assignments to +internal variables, such as \texttt{outputtemplate}, or a \LaTeX\ +preamble declaration for enhanced text rendering. +Comments\index{comments} in MetaPost code are introduced by the percent +sign~\verb|%|\index{\%?\texttt{\%}!comment}, which causes the remainder +of the current line to be ignored. + +The remainder of this section briefly introduces three assignments to +internal variables, each one useful by itself, that can often be found +in MetaPost input files: +$$ +\begin{verbatim}[commandchars=\\\{\}] +prologues := 3; \smallskip +outputtemplate := "%j-%c.mps"; \smallskip +outputformat := "svg"; +\end{verbatim} +$$ + +If your graphics contain text labels, you might want to set variable +\texttt{prologues} to~3 to make sure the correct fonts are used under +all possible circumstances. The second assignment changes the output +file naming scheme to the form \texttt{\tdescr{jobname}-\tdescr{n}.mps}. +That way, instead of a numeric index, all output files get a uniform +file extension \texttt{mps}\index{mps file?{\tt mps} + file}\index{files!mps?{\tt mps}}, which is typically used for +MetaPost's PostScript output. The last assignment lets MetaPost write +output files in the SVG format rather than in the PostScript format. +More information can be found in Sections~\ref{Dprologues} +and~\ref{workflow2}. + + +\section{Curves} +\label{curves} + +MetaPost is perfectly happy to draw curved lines as well as straight ones. +A \verb|draw| statement with the points separated by +\verb|..|\index{..?\texttt{..}} draws a smooth curve through the points. +For example consider the result of +$$ \hbox{\verb|draw z0..z1..z2..z3..z4|} $$ +after defining five points as follows: +$$\begin{verbatim} +z0 = (0,0); z1 = (60,40); +z2 = (40,90); z3 = (10,70); +z4 = (30,50); +\end{verbatim} +$$ +Figure~\ref{fig2} shows the curve with points \verb|z0| through \verb|z4| +labeled. + +\begin{figure}[htp] +$$ \includegraphics{mpman-3.mps} +$$ +\caption[A curve through points 0, 1, 2, 3, and 4] + {The result of {\tt draw z0..z1..z2..z3..z4}} +\label{fig2} +\end{figure} + +There are many other ways to draw a curved path through the same five +points. To make a smooth closed curve, connect \verb|z4| back to the +beginning by appending \verb|..cycle|\index{cycle?\texttt{cycle}} to the +\verb|draw| statement as shown in Figure~\ref{fig3}a. It is also +possible in a single \verb|draw| statement to mix curves and straight +lines as shown in Figure~\ref{fig3}b. Just use \verb|--| where you want +straight lines and \verb|..| where you want curves. Thus +$$ \hbox{\verb|draw z0..z1..z2..z3--z4--cycle|} $$ +produces a curve through points 0,~1, 2, and~3, then a polygonal line from +point~3 to point~4 and back to point~0. The result is essentially the same +as having two draw statements +\begin{eqnarray*} + \hbox{\verb|draw z0..z1..z2..z3|}\\ +\noalign{\hbox{and}} + \hbox{\verb|draw z3--z4--z0|} +\end{eqnarray*} + +\begin{figure}[htp] +$$ {\includegraphics{mpman-104.mps} \atop (a)} + \qquad {\includegraphics{mpman-204.mps} \atop (b)} +$$ +\caption[Closed curves through five points] + {(a)~The result of {\tt draw z0..\linebreak[0]z1..\linebreak[0]% + z2..\linebreak[0]z3..\linebreak[0]z4..\linebreak[0]cycle}; + (b)~the result of {\tt draw z0..\linebreak[0]z1..\linebreak[0]% + z2..\linebreak[0]z3--\linebreak[0]z4--\linebreak[0]cycle}.} +\label{fig3} +\end{figure} + +MetaPost already provides a small selection of basic path shapes that +can be used to derive custom paths from. The predefined variable +\texttt{fullcircle}\index{fullcircle?\texttt{fullcircle}}\label{Dfcirc} +refers to a closed path describing a circle of unit diameter centered on +the origin. There are also +\texttt{halfcircle}\index{halfcircle?\texttt{halfcircle}}\label{Dhcirc} +and +\texttt{quartercircle}\index{quartercircle?\texttt{quartercircle}}\label{Dqcirc}, +the former being the part of a full circle covering the first and second +quadrant and the latter covering just the first quadrant. Because of +the mathematical model that is used to describe paths in MetaPost, all +these are not exactly circular paths, but very good approximations (see +Figure~\ref{fig3a}). + +\begin{figure} +$$ \includegraphics{mpman-61.mps} $$ +\caption{A circle and a square with cardinal points. Arrows are + pointing to the start and end points of the closed paths.} +\label{fig3a} +\end{figure} + +Rectangularly shaped paths can be derived from +\texttt{unitsquare}\index{unitsquare?\texttt{unitsquare}}\label{Dunitsqr}, +a closed path describing a square of unit side length whose lower left +corner is located at the origin. + +\subsection{B\'ezier Cubic Curves} + +When MetaPost is asked to draw a smooth curve through a sequence of +points, it constructs a piecewise cubic curve with continuous slope and +approximately continuous curvature\index{curvature}. This means that a +path specification such as +$$ \hbox{\verb|z0..z1..z2..z3..z4..z5|} $$ +results in a curve that can be defined parametrically\index{parameterization} +as $(X(t),Y(t))$ for +$0\le t\le5$, where $X(t)$ and $Y(t)$ are piecewise cubic functions. That is, +there is a different pair of cubic functions for each integer-bounded +$t$-interval. If ${\tt z0}=(x_0,y_0)$, ${\tt z1}=(x_1,y_1)$, +${\tt z2}=(x_2,y_2)$, \ldots, MetaPost selects +B\'ezier control\index{control points} points +$(x_0^+,y_0^+)$, $(x_1^-,y_1^-)$, $(x_1^+,y_1^+)$, \ldots, where +\begin{eqnarray*} + X(t+i) &=& (1-t)^3x_i + 3t(1-t)^2x_i^+ + 3t^2(1-t)x_{i+1}^- + t^3x_{i+1},\\ + Y(t+i) &=& (1-t)^3y_i + 3t(1-t)^2y_i^+ + 3t^2(1-t)y_{i+1}^- + t^3y_{i+1} +\end{eqnarray*} +for $0\le t\le1$. The precise rules for choosing the B\'ezier control points +are described in \cite{ho:splin} and in {\sl The \MF book\/}~\cite{kn:c}. + +In order for the path to have a continuous slope at $(x_i,y_i)$, the incoming +and outgoing directions at $(X(i),Y(i))$ must match. Thus the vectors +$$ (x_i-x_i^-,\,y_i-y_i^-) \qquad \hbox{and} + \qquad (x_i^+-x_i,\,y_i^+-y_i) +$$ +must have the same direction; i.e., $(x_i,y_i)$ must be on the line segment +between $(x_i^-,y_i^-)$ and $(x_i^+,y_i^+)$. This situation is illustrated +in Figure~\ref{fig4} where the B\'ezier control points selected by MetaPost +are connected by dashed lines. For those who are familiar with the interesting +properties of this construction, MetaPost allows the control points to be +specified directly in the following format:\index{controls?\texttt{controls}} +$$ \begin{verbatim} +draw (0,0)..controls (26.8,-1.8) and (51.4,14.6) + ..(60,40)..controls (67.1,61.0) and (59.8,84.6) + ..(40,90)..controls (25.4,94.0) and (10.5,84.5) + ..(10,70)..controls ( 9.6,58.8) and (18.8,49.6) + ..(30,50); +\end{verbatim} +$$ + +For a way to extract the control points of a path, given by the user or +calculated by MetaPost, see section~\ref{Dprepostctrl}. + +\begin{figure}[htp] +$$ \includegraphics{mpman-5.mps} +$$ +\caption[A curve and the control polygon] + {The result of {\tt draw z0..z1..z2..z3..z4} with the + automatically-selected B\'ezier control polygon illustrated by dashed + lines.} +\label{fig4} +\end{figure} + +\subsection{Specifying Direction, Tension, and Curl} +\label{tenscurl} + +MetaPost provides many ways of controlling the behavior of a curved path +without actually specifying the control points. For instance, some +points on the path may be selected as vertical or horizontal extrema. +If \verb|z1| is to be a horizontal extreme and \verb|z2| is to be a +vertical extreme, you can specify that $(X(t),Y(t))$ should go upward at +\verb|z1| and to the left at \verb|z2|: +$$ \hbox{\verb|draw z0..z1{up}..z2{left}..z3..z4;|} $$ +The resulting shown in Figure~\ref{fig5} has the desired vertical and +horizontal directions at \verb|z1| and \verb|z2|, but it does not look +as smooth as the curve in Figure~\ref{fig2}. The reason is the large +discontinuity in curvature\index{curvature} at \verb|z1|. If it were +not for the specified direction at \verb|z1|, the MetaPost interpreter +would have chosen a direction designed to make the curvature above +\verb|z1| almost the same as the curvature below that point. + +\begin{figure}[htp] +$$ \includegraphics{mpman-6.mps} +$$ +\caption[A curve and the control polygon] + {The result of {\tt draw z0..z1\char`\{up\char`\}..z2\char`\{left\char`\}% + ..z3..z4}.} +\label{fig5} +\end{figure} + +How can the choice of directions at given points on a curve determine whether +the curvature will be continuous? The reason is that curves used in MetaPost +come from a family where a path is determined by its endpoints and the +directions there. Figures \ref{fig6} and~\ref{fig7} give a good idea of what +this family of curves is like. + +\begin{figure}[htp] +$$ \mathcenter{\includegraphics{mpman-7.mps}} \quad +\begin{verbatim} +beginfig(7) +for a=0 upto 9: + draw (0,0){dir 45}..{dir -10a}(6cm,0); +endfor +endfig; +\end{verbatim} +$$ +\caption{A curve family and the MetaPost instructions for generating it} +\label{fig6} +\end{figure} + +\begin{figure}[htp] +$$ \mathcenter{\includegraphics{mpman-8.mps}} \quad +\begin{verbatim} +beginfig(8) +for a=0 upto 7: + draw (0,0){dir 45}..{dir 10a}(6cm,0); +endfor +endfig; +\end{verbatim} +$$ +\caption{Another curve family with the corresponding MetaPost instructions} +\label{fig7} +\end{figure} + +Figures \ref{fig6} and~\ref{fig7} illustrate a few new MetaPost +features. The first is the {\tt +dir}\index{dir?\texttt{dir}}\label{Ddirop} operator that takes an angle +in degrees and generates a unit vector in that direction. Thus +\verb|dir 0| is equivalent to {\tt +right}\index{right?\texttt{right}}\label{Dright} and \verb|dir 90| is +equivalent to {\tt up}\index{up?\texttt{up}}\label{Dup}. There are also +predefined direction vectors {\tt +left}\index{left?\texttt{left}}\label{Dleft} and {\tt +down}\index{down?\texttt{down}}\label{Ddown} for {\tt dir 180} and {\tt +dir 270}. + +The direction +vectors given in \verb|{}| can be of any length, and they can come before a +point as well as after one. It is even possible for a path specification +to have directions given before and after a point. For example a path +specification containing +$$ \hbox{\verb|..{dir 60}(10,0){up}..|} $$ +produces a curve with a corner at $(10,0)$. + +Note that some of the curves in Figure~\ref{fig6} have points of +inflection\index{inflections}. This is necessary in order to produce +smooth curves in situations like Figure~\ref{fig3}a, but it is probably +not desirable when dealing with vertical and horizontal extreme points +as in Figure~\ref{fig8}a. If \verb|z1| is supposed to be the topmost +point on the curve, this can be achieved by using +\verb|...|\index{...?\texttt{...}} instead of \verb|..| in the path +specification as shown in Figure~\ref{fig8}b. The meaning of \verb|...| +is ``choose an inflection-free path between these points unless the +endpoint directions make this impossible.'' (It would be possible to +avoid inflections in Figure~\ref{fig6}, but not in Figure~\ref{fig7}). + +\begin{figure}[htp] +$$ {\mathcenter{\includegraphics{mpman-109.mps}} \atop + \hbox{\verb|draw z0{up}..z1{right}..z2{down}|}} + \quad + {\mathcenter{\includegraphics{mpman-209.mps}} \atop + \hbox{\verb|draw z0{up}...z1{right}...z2{down}|}} +$$ +\caption{Two {\tt draw} statements and the resulting curves.} +\label{fig8} +\end{figure} + +Another way to control a misbehaving path is to increase the +``tension''\index{tension} parameter. Using \verb|..| in a path +specification sets the tension parameter to the default value~1. If +this makes some part of a path a little too wild, we can selectively +increase the tension. If Figure~\ref{fig9}a is considered ``too wild,'' +a {\tt draw} statement of the following form increases the tension +between {\tt z1} and {\tt z2}: +$$ \hbox{\verb|draw z0..z1..tension 1.3..z2..z3|} $$ +This produces Figure~\ref{fig9}b. For an asymmetrical effect like +Figure~\ref{fig9}c, the \verb|draw| statement becomes +$$ \hbox{\verb|draw z0..z1..tension 1.5 and 1..z2..z3|} $$ +The tension parameter can be less than one, but it must be at least $3\over4$. + +\begin{figure}[htp] +$$ {\mathcenter{\includegraphics{mpman-110.mps}} \atop (a)} + \quad + {\mathcenter{\includegraphics{mpman-210.mps}} \atop (b)} + \quad + {\mathcenter{\includegraphics{mpman-310.mps}} \atop (c)} +$$ +\caption[Effects of changing the tension parameter] + {Results of {\tt draw z0..z1..tension} $\alpha$ {\tt and} $\beta$ + {\tt ..z2..z3} for various $\alpha$ and $\beta$: + (a)~$\alpha=\beta=1$; (b)~$\alpha=\beta=1.3$; + (c)~$\alpha=1.5$, $\beta=1$.} +\label{fig9} +\end{figure} + +MetaPost paths also have a parameter called +``curl''\index{curl?\texttt{curl}} that affects the ends of a path. In +the absence of any direction specifications, the first and last segments +of a non-cyclic path are approximately circular arcs as in the $c=1$ +case of Figure~\ref{fig10}. To use a different value for the curl +parameter, specify \verb|{curl c}| for some other value of $c$. Thus +$$ \hbox{\verb|draw z0{curl c}..z1..{curl c}z2|} $$ +sets the curl parameter for \verb|z0| and \verb|z2|. Small values of +the curl parameter reduce the curvature\index{curvature} at the +indicated path endpoints, while large values increase the curvature as +shown in Figure~\ref{fig10}. In particular, a curl value of zero makes +the curvature approach zero. + +\begin{figure}[htp] +$$ {\mathcenter{\includegraphics{mpman-111.mps}} \atop c=0} + \qquad + {\mathcenter{\includegraphics{mpman-211.mps}} \atop c=1} + \qquad + {\mathcenter{\includegraphics{mpman-311.mps}} \atop c=2} + \qquad + {\mathcenter{\includegraphics{mpman-411.mps}} \atop c=\infty} +$$ +\caption[Effects of changing the curl parameter] + {Results of {\tt draw z0\char`\{curl c\char`\}..z1..% + \char`\{curl c\char`\}z2} for various values + of the curl parameter~$c$.} +\label{fig10} +\end{figure} + +\subsection{Summary of Path Syntax} + +There are a few other features of MetaPost path syntax, but they are +relatively unimportant. Since \MF\ uses the same path syntax, +interested readers can refer to \cite[chapter 14]{kn:c}. The summary of +path syntax in Figure~\ref{sypath} includes everything discussed so far +including the \verb|--| and \verb|...| constructions which \cite{kn:c} +shows to be macros rather than primitives. A few comments on the +semantics are in order here: If there is a non-empty $\descr{direction +specifier}$ before a $\descr{path knot}$ but not after it, or vice +versa, the specified direction (or curl amount) applies to both the +incoming and outgoing path segments. A similar arrangement applies when +a $\descr{controls}$ specification gives only one $\descr{pair +primary}$. Thus +$$ \hbox{\verb|..controls (30,20)..|} $$ +is equivalent to +$$ \hbox{\verb|...controls (30,20) and (30,20)..|} $$ + +\begin{figure}[htp] +\begin{ctabbing} +$\descr{path expression} \rightarrow + \descr{path subexpression}$\\ +\qquad \= ${}\mid \descr{path subexpression} \descr{direction specifier}$\\ +\> ${}\mid \descr{path subexpression} \descr{path join}$ \verb|cycle|\\ +$\descr{path subexpression} \rightarrow + \descr{path knot}$\\ +\> ${}\mid \descr{path expression} \descr{path join} \descr{path knot}$\\ +$\descr{path join} \rightarrow + \hbox{\verb|--|}$\\ +\> ${}\mid \descr{direction specifier} \descr{basic path join} + \descr{direction specifier}$\\ +$\descr{direction specifier} \rightarrow + \descr{empty}$\\ +\> ${}\mid {}$\verb|{curl| $\descr{numeric expression}$\verb|}|\\ +\> ${}\mid {}$\verb|{|$\descr{pair expression}$\verb|}|\\ +\> ${}\mid {}$\verb|{|$\descr{numeric expression}$\verb|,|% + $\descr{numeric expression}$\verb|}|\\ +$\descr{basic path join} \rightarrow + \hbox{\verb|..|} + \mid \hbox{\verb|...|} + \mid \hbox{\verb|..|}\descr{tension}\hbox{\verb|..|} + \mid \hbox{\verb|..|}\descr{controls}\hbox{\verb|..|}$\\ +$\descr{tension} \rightarrow + \hbox{\verb|tension|}\descr{numeric primary}$\\ +\> ${}\mid \hbox{\verb|tension|}\descr{numeric primary} + \hbox{\verb|and|}\descr{numeric primary}$\\ +$\descr{controls} \rightarrow + \hbox{\verb|controls|}\descr{pair primary}$\\ +\> ${}\mid \hbox{\verb|controls|}\descr{pair primary} + \hbox{\verb|and|}\descr{pair primary}$ +\end{ctabbing} +\caption{The syntax for path construction} +\label{sypath} +\end{figure} + +A pair of coordinates like \verb|(30,20)| or a \verb|z| variable that +represents a coordinate pair is what Figure~\ref{sypath} calls a +$\descr{pair primary}$. A $\descr{path knot}$ is similar except that it +can take on other forms such as a path expression in parentheses. +Primaries and expressions of various types will be discussed in full +generality in Section~\ref{exprs}. + + +\section{Linear Equations} +\label{lin.eq} + +An important feature taken from \MF\ is the ability to solve linear +equations so that programs can be written in a partially declarative fashion. +For example, the MetaPost interpreter can read +$$ \hbox{\verb|a+b=3; 2a=b+3;|} $$ +and deduce that $a=2$ and $b=1$. The same equations can be written +slightly more compactly by stringing them together with multiple equal +signs: +$$ \hbox{\verb|a+b = 2a-b = 3;|} $$ +Whichever way you give the equations, you can then give the +command\index{show?\texttt{show}} +$$ \hbox{\tt show a,b;} $$ +to see the values of {\tt a} and {\tt b}. MetaPost responds by typing +$$\begin{verbatim} +>> 2 +>> 1 +\end{verbatim} +$$ + +Note that {\tt =}\index{=?\texttt{=}} is not an assignment operator; it +simply declares that the left-hand side equals the right-hand side. +Thus {\tt a=a+1} produces an error message complaining about an +``inconsistent equation\index{Inconsistent equation?\texttt{Inconsistent +equation}}.'' The way to increase the value of {\tt a} is to use the +assignment\index{assignment} operator {\tt :=}\index{:=?\texttt{:=}} as +follows: +$$ \hbox{\tt a:=a+1;} $$ +In other words, {\tt :=} is for changing existing values while {\tt =} is for +giving linear equations to solve. + +There is no restriction against mixing equations and assignment +operations as in the following example: +$$ \hbox{\tt a = 2; b = a; a := 3; c = a;} $$ +After the first two equations set {\tt a} and~{\tt b} equal to 2, the +assignment operation changes {\tt a} to~3 without affecting {\tt b}. +The final value of {\tt c} is 3 since it is equated to the new value of +{\tt a}. In general, an assignment operation is interpreted by first +computing the new value, then eliminating the old value from all +existing equations before actually assigning the new value. + +\subsection{Equations and Coordinate Pairs} + +MetaPost can also solve linear equations involving coordinate pairs. We have +already seen many trivial examples of this in the form of equations like +$$ \hbox{\verb|z1=(0,.2in)|} $$ +Each side of the equation must be formed by adding or subtracting +coordinate pairs and multiplying or dividing them by known numeric +quantities. Other ways of naming pair-valued variables will be +discussed later, but the ${\tt z}\descr{number}$\index{z convention?{\tt +z} convention} is convenient because it is an abbreviation for +$$ \hbox{\tt (x}\descr{number} \hbox{\tt, y}\descr{number}\hbox{\tt)} $$ +This makes it possible to give values to \verb|z| variables by giving +equations involving their coordinates. For instance, points {\tt z1}, +{\tt z2}, {\tt z3}, and~{\tt z6} in Figure~\ref{fig12} were initialized +via the following equations: +\begin{eqnarray*} + &&\hbox{\verb|z1=-z2=(.2in,0);|} \\ + &&\hbox{\verb|x3=-x6=.3in;|} \\ + &&\hbox{\verb|x3+y3=x6+y6=1.1in;|} +\end{eqnarray*} +Exactly the same points could be obtained by setting their values directly: +$$ \begin{verbatim} +z1=(.2in,0); z2=(-.2in,0); +z3=(.3in,.8in); z6=(-.3in,1.4in); +\end{verbatim} +$$ + +After reading the equations, the MetaPost interpreter knows the values +of {\tt z1}, {\tt z2}, {\tt z3}, and~{\tt z6}. The next step in the +construction of Figure~\ref{fig12} is to define points {\tt z4} and {\tt +z5} equally spaced along the line from {\tt z3} to {\tt z6}. Since this +operation comes up often, MetaPost has a special syntax for it. This +mediation construction\index{mediation}\index{[]?\texttt{[]}!mediation} +$$ \hbox{\verb|z4=1/3[z3,z6]|} $$ +means that {\tt z4} is $1\over3$ of the way from $z3$ to $z6$; i.e., +$$ {\tt z4}={\tt z3}+{1\over3}({\tt z6}-{\tt z3}). $$ +Similarly +$$ \hbox{\verb|z5=2/3[z3,z6]|} $$ +makes {\tt z5} $2\over3$ of the way from $z3$ to $z6$. + +\begin{figure}[htp] +$$ \begin{verbatim} +beginfig(13); +z1=-z2=(.2in,0); +x3=-x6=.3in; +x3+y3=x6+y6=1.1in; +z4=1/3[z3,z6]; +z5=2/3[z3,z6]; +z20=whatever[z1,z3]=whatever[z2,z4]; +z30=whatever[z1,z4]=whatever[z2,z5]; +z40=whatever[z1,z5]=whatever[z2,z6]; +draw z1--z20--z2--z30--z1--z40--z2; +pickup pencircle scaled 1pt; +draw z1--z2; +draw z3--z6; +endfig; +\end{verbatim} +\quad \mathcenter{\includegraphics{mpman-13.mps}} +$$ +\caption[MetaPost code and figure using linear equations] + {MetaPost commands and the resulting figure. Point labels have been + added to the figure for clarity.} +\label{fig12} +\end{figure} + +Mediation can also be used to say that some point is at an unknown +position along the line between two known points. For instance, we +could a introduce new variable {\tt aa} and write something like +$$ \hbox{\verb|z20=aa[z1,z3];|} $$ +This says that {\tt z20} is some unknown fraction {\tt aa} of the way +along the line between {\tt z1} and {\tt z3}. Another such equation +involving a different line is sufficient to fix the value of {\tt z20}. +To say that {\tt z20} is at the intersection of the {\tt z1}-{\tt z3} +line and the {\tt z2}-{\tt z4} line, introduce another variable {\tt ab} +and set +$$ \hbox{\verb|z20=ab[z2,z4];|} $$ +This allows MetaPost to solve for {\tt x20}, {\tt y20}, {\tt aa}, and {\tt ab}. + +It is a little painful to keep thinking up new names like {\tt aa} and +{\tt ab}. This can be avoided by using a special feature called {\tt +whatever}\index{whatever?\texttt{whatever}}\label{Dwhatev}. This macro +generates a new anonymous variable each time it appears. Thus the +statement +$$ \hbox{\verb|z20=whatever[z1,z3]=whatever[z2,z4]|} $$ +sets {\tt z20} as before, except it uses {\tt whatever} to generate two +{\em different\/} anonymous variables instead of {\tt aa} and {\tt ab}. +This is how Figure~\ref{fig12} sets {\tt z20}, {\tt z30}, and +{\tt z40}. + +\subsection{Dealing with Unknowns} + +A system of equations such as those used in Figure~\ref{fig12} can be given in +any order as long as all the equations are linear and all the variables can +be determined before they are needed. This means that the equations +\begin{eqnarray*} + && \hbox{\verb|z1=-z2=(.2in,0);|}\\ + && \hbox{\verb|x3=-x6=.3in;|}\\ + && \hbox{\verb|x3+y3=x6+y6=1.1in;|}\\ + && \hbox{\verb|z4=1/3[z3,z6];|}\\ + && \hbox{\verb|z5=2/3[z3,z6];|} +\end{eqnarray*} +suffice to determine {\tt z1} through {\tt z6}, no matter what order the +equations are given in. On the other hand +$$ \hbox{\verb|z20=whatever[z1,z3]|} $$ +is legal only when a known value has previously been specified for the difference +${\tt z3}-{\tt z1}$, because the equation is equivalent +to\index{mediation} +$$ \hbox{\verb|z20 = z1 + whatever*(z3-z1)|} $$ +and the linearity requirement disallows multiplying unknown components +of ${\tt z3}-{\tt z1}$ by the anonymous unknown result of {\tt +whatever}. The general rule is that you cannot multiply two unknown +quantities or divide by an unknown quantity, nor can an unknown quantity +be used in a {\tt draw} statement. Since only linear equations are +allowed, the MetaPost interpreter can easily solve the equations and +keep track of what values are known. + +The most natural way to ensure that MetaPost can handle an expression like +$$ \hbox{\verb|whatever[z1,z3]|} $$ +is to ensure that {\tt z1} and {\tt z3} are both known. However this is not +actually required since MetaPost may be able to deduce a known value for +${\tt z3}-{\tt z1}$ before either of {\tt z1} and {\tt z3} are known. +For instance, MetaPost will accept the equations +$$ \hbox{\verb|z3=z1+(.1in,.6in); z20=whatever[z1,z3];|} $$ +but it will not be able to determine any of the components of {\tt z1}, +{\tt z3}, or {\tt z20}. + +These equations do give partial information about {\tt z1}, {\tt z3}, +and {\tt z20}. A good way to see this is to give another equation such as +$$ \hbox{\verb|x20-x1=(y20-y1)/6;|} $$ +This produces the error message ``{\tt ! Redundant +equation}\index{Redundant equation?\texttt{Redundant equation}}.'' +MetaPost assumes that you are trying to tell it something new, so it +will usually warn you when you give a redundant equation. If the new +equation had been +$$ \hbox{\verb|(x20-x1)-(y20-y1)/6=1in;|} $$ +the error message would have been\index{Inconsistent +equation?\texttt{Inconsistent equation}} +$$ \hbox{\verb|! Inconsistent equation (off by 71.99979).|} $$ +This error message illustrates +roundoff\index{roundoff error} error in MetaPost's linear equation solving +mechanism. Roundoff error +is normally not a serious problem, but it is likely to cause trouble if you are +trying to do something like find the intersection of two lines that are almost +parallel. + + +\section{Expressions} +\label{exprs} + +It is now time for a more systematic view of the MetaPost language. We +have seen that there are numeric quantities and coordinate pairs, and +that these can be combined to specify paths for {\tt draw} statements. +We have also seen how variables can be used in linear equations, but we +have not discussed all the operations and data types that can be used in +equations. + +It is possible to experiment with expressions involving any of the data types +mentioned below by using the statement\index{show?\texttt{show}}\label{Dshow} +$$ {\tt show}\, \descr{expression} $$ +to ask MetaPost to print a symbolic representation of the value of each +expression. For known numeric values, each is printed on a new line +preceded by ``\verb|>> |''. Other types of result are printed similarly, +except that complicated values are sometimes not printed on standard +output. This produces a reference to the transcript +file\index{files!transcript} that looks like this: +$$ \hbox{\verb|>> picture (see the transcript file)|} $$ +If you want to the full results of {\tt show} statements to be printed +on your terminal, assign a positive value to the internal\index{internal +variables} variable\index{variables!internal} {\tt +tracingonline}\index{tracingonline?\texttt{tracingonline}}\label{Dtonline}. + +\subsection{Data Types} +\label{datatypes} + +MetaPost actually has ten basic data types\index{types}: numeric, pair, +path, transform, (rgb)color, cmykcolor, string, boolean, picture, and +pen. Let us consider these one at a time beginning with the numeric +type. + +Numeric\index{numeric type} quantities in MetaPost are represented in +fixed point arithmetic\index{arithmetic} as integer multiples of +$1\over65536$, the smallest positive value, which is also available as +the predefined constant +\texttt{epsilon}\index{epsilon?\texttt{epsilon}}\label{Depsilon}.\footnote{MetaPost + can also do arithmetic with higher and (almost) arbitrary precision. + See Appendix~\ref{hparith} for more information.} Numeric quantities +must normally have absolute values less than 4096 but intermediate +results can be eight times larger. This should not be a problem for +distances or coordinate values since 4096 PostScript points is more than +1.4~meters. If you need to work with numbers of magnitude 4096 or more, +setting the internal variable +\texttt{warningcheck}\index{warningcheck?\texttt{warningcheck}}\label{Dwarncheck} +to zero suppresses the warning messages about large numeric quantities. + +The pair\index{pair type} type is represented as a pair of numeric +quantities. We have seen that pairs are used to give coordinates in +{\tt draw} statements. Pairs can be added, subtracted, used in +mediation expressions, or multiplied or divided by numerics. + +Paths\index{path type} have already been discussed in the context of {\tt draw} +statements, but +that discussion did not mention that paths are first-class objects that can be +stored and manipulated. A path represents a straight or curved line that is +defined parametrically. + +Another data type represents an arbitrary affine +transformation\index{transform type}. A {\em transform\/} can be any +combination of rotating, scaling, slanting, and shifting. If ${\tt +p}=(p_x,p_y)$ is a pair and {\tt T} is a +transform,\index{transformed?\texttt{transformed}} +$$ \hbox{\tt p transformed T} $$ +is a pair of the form +$$ (t_x+t_{xx}p_x+t_{xy}p_y, t_y+t_{yx}p_x+t_{yy}p_y), $$ +where the six numeric quantities $(t_x,t_y,t_{xx},t_{xy},t_{yx},t_{yy})$ +determine {\tt T}. Transforms can also be applied to paths, pictures, pens, +and transforms. + +The color\index{color type} type is like the pair type, except +that it has three components instead of two and each component is +normally between 0 and 1. Like pairs, colors can be added, +subtracted, used in mediation expressions, or multiplied or divided +by numerics. Colors can be specified in terms of the predefined +constants \ttindex{black}\label{Dblack}, \ttindex{white}\label{Dwhite}, +\ttindex{red}\label{Dred}, \ttindex{green}\label{Dgreen}, +\ttindex{blue}\label{Dblue}, or the red, green, and +blue components can be given explicitly. Black is {\tt (0,0,0)} and +white is {\tt (1,1,1)}. A level of gray such as {\tt (.4,.4,.4)} can also be +specified as {\tt 0.4white}. Although color typed variables may be +any ordered triplet, when adding an object to a picture, MetaPost will +convert its color by clipping each component between 0 and 1. For +example, MetaPost will output the color (1,2,3) as (1,1,1). +MetaPost solves linear equations involving +colors the same way it does for pairs. The type `rgbcolor' is an alias of +type `color'. + +The cmykcolor\index{cmykcolor type} type is similar +to the color type except that it has four components instead of +three. This type is used to specify colors by their cyan, magenta, +yellow, and black components explicitly. Because CMYK colors deal with +pigments instead of light rays, the color white would be expressed as +{\tt (0,0,0,0)} and black as {\tt (0,0,0,1)}. In theory, the colors +{\tt ($c$,$m$,$y$,1)} and {\tt (1,1,1,$k$)} should result in black for +any values of $c$, $m$, $y$ and~$k$, too. But in practice, this is +avoided since it is a waste of colored ink and can lead to +unsatisfactory results. + +A string\index{string type} represents a sequence of characters. +String constants\index{string constants} are given +in double quotes \hbox{\verb|"like this"|}. String constants cannot contain +double quotes or newlines, but there is a way to construct a string containing +any sequence of eight-bit characters. + +\label{Dscantokens} +Conversion from strings to other types, notably numeric, can be accomplished by +the {\tt scantokens}\index{scantokens?\texttt{scantokens}} primitive: +\begin{center}\texttt{n := scantokens(}\textit{str}\texttt{);}\end{center} +More generally, \texttt{scantokens} parses a string into a token +sequence, as if MetaPost had read it as input. + +The boolean\index{boolean type} type has the constants {\tt +true}\index{true?\texttt{true}}\label{Dtrue} and {\tt +false}\index{false}\label{Dfalse} and the operators {\tt +and}\index{and?\texttt{and}}\label{Dand}, {\tt +or}\index{or?\texttt{or}}\label{Dor}, {\tt +not}\index{not?\texttt{not}}\label{Dnot}. The relations \verb|=| and +\verb|<>|\index{<>?\texttt{<>}}\label{Dcmpar} test objects of any type +for equality and inequality\index{inequality}. +Comparison\index{comparison} relations \verb|<|\index{<?\texttt{<}}, +\verb|<=|\index{<=?\texttt{<=}}, \verb|>|\index{>?\texttt{>}}, and +\verb|>=|\index{>=?\texttt{>=}} are defined lexicographically for +strings and in the obvious way for numerics. Ordering relations are +also defined for booleans, pairs, colors, and transforms, but the +comparison rules are not worth discussing here. + +The picture\index{picture type} data type is just what the name implies. +Anything that can be drawn in MetaPost can be stored in a picture +variable. In fact, the {\tt draw}\index{draw?\texttt{draw}} statement +actually stores its results in a special picture variable called {\tt +currentpicture}\index{currentpicture?\texttt{currentpicture}}. Pictures +can be added to other pictures and operated on by transforms. + +Finally, there is a data type called a pen\index{pen type}. The main +function of pens in MetaPost is to determine line thickness, but they +can also be used to achieve calligraphic effects. The +statement\index{pickup?\texttt{pickup}}\label{Dpickup} +$$ {\tt pickup\ }\descr{pen expression} $$ +causes the given pen to be used in subsequent +\verb|draw|\index{draw?\texttt{draw}} or +\verb|drawdot|\index{drawdot?\texttt{drawdot}} statements. Normally, +the pen expression is of the form +$$ {\tt pencircle\ scaled\ }\descr{numeric primary}. $$ +This defines a circular pen that produces lines of constant thickness. +If calligraphic effects are desired, the pen expression can be adjusted to give +an elliptical pen or a polygonal pen. + +\subsection{Operators} + +There are many different ways to make expressions of the ten basic +types, but most of the operations fit into a fairly simple syntax with +four levels of precedence as shown in Figure~\ref{syexpr}. There are +primaries\index{primary?\tdescr{primary}}, +secondaries\index{secondary?\tdescr{secondary}}, +tertiaries\index{tertiary?\tdescr{tertiary}}, and +expressions\index{expression?\tdescr{expression}} of each of the basic +types, so the syntax rules could be specialized to deal with items such +as \tdescr{numeric primary}, \tdescr{boolean tertiary}, etc. This +allows the result type for an operation to depend on the choice of +operator and the types of its operands. For example, the {\tt <} +relation is a \tdescr{tertiary binary} that can be applied to a +\tdescr{numeric expression} and a \tdescr{numeric tertiary} to give a +\tdescr{boolean expression}. The same operator can accept other operand +types such as \tdescr{string expression} and \tdescr{string tertiary}, +but an error message results if the operand types do not match. + +\begin{figure}[htp] +\begin{ctabbing} +$\tt \descr{primary} \rightarrow \descr{variable}$\\ +$\tt \qquad \;|\; \hbox{\tt (}\descr{expression}\hbox{\tt )}$\\ +$\tt \qquad \;|\; \descr{nullary op}$\\ +$\tt \qquad \;|\; \descr{of operator} \descr{expression} + of \descr{primary}$\\ +$\tt \qquad \;|\; \descr{unary op} \descr{primary}$\\ +$\tt \descr{secondary} \rightarrow \descr{primary}$\\ +$\tt \qquad \;|\; \descr{secondary} \descr{primary binop} \descr{primary}$\\ +$\tt \descr{tertiary} \rightarrow \descr{secondary}$\\ +$\tt \qquad \;|\; \descr{tertiary} \descr{secondary binop} + \descr{secondary}$\\ +$\tt \descr{expression} \rightarrow \descr{tertiary}$\\ +$\tt \qquad \;|\; \descr{expression} \descr{tertiary binop} + \descr{tertiary}$ +\end{ctabbing} +\caption{The overall syntax rules for expressions} +\index{unary op?\tdescr{unary op}} \index{nullary op?\tdescr{nullary op}} +\index{primary binop?\tdescr{primary binop}} +\index{secondary binop?\tdescr{secondary binop}} +\index{tertiary binop?\tdescr{tertiary binop}} +\label{syexpr} +\end{figure} + +The multiplication and division operators {\tt *}\label{Dmldiv} and~{\tt +/} are examples of what Figure~\ref{syexpr} calls a \tdescr{primary +binop}. Each can accept two numeric operands or one numeric operand and +one operand of type pair or color. The exponentiation operator +\verb|**|\index{**?\texttt{**}}\index{exponentiation}\label{Dpow} is a +\tdescr{primary binop} that requires two numeric operands. Placing this +at the same level of precedence as multiplication and division has the +unfortunate consequence that \verb|3*a**2| means $(3a)^2$, not +$3(a^2)$\index{parsing irregularities}. Since unary +negation\label{Dneg} applies at the primary level, it also turns out +that \verb|-a**2| means $(-a)^2$. Fortunately, subtraction has lower +precedence so that \verb|a-b**2| does mean $a-(b^2)$ instead of +$(a-b)^2$. + +Another \tdescr{primary binop} is the {\tt +dotprod}\index{dotprod?\texttt{dotprod}}\label{Ddprod} operator that +computes the vector dot product of two pairs. For example, {\tt z1 +dotprod z2} is equivalent to {\tt x1*x2 + y1*y2}. + +The additive operators {\tt +} and {\tt -}\label{Dadd} are +\tdescr{secondary binops} that operate on numerics, pairs, or colors and +produce results of the same type. Other operators that fall in this +category are ``Pythagorean addition'' +\verb|++|\index{++?\texttt{++}}\label{Dpyadd} and ``Pythagorean +subtraction'' \verb|+-+|\index{+-+?\texttt{+-+}}\label{Dpysub}: +\verb|a++b| means $\sqrt{a^2+b^2}$ and \verb|a+-+b| means +$\sqrt{a^2-b^2}$. There are too many other operators to list here, but +some of the most important are the boolean operators {\tt +and}\index{and?\texttt{and}} and {\tt or}\index{or?\texttt{or}}. The +{\tt and} operator is a \tdescr{primary binop} and the {\tt or} operator +is a \tdescr{secondary binop}. + +The basic operations on strings are concatenation\index{concatenation}, +substring construction and calculating the length of a string. +The \tdescr{tertiary binop} \verb|&|\index{&?\texttt{\&}}\label{Damp} +implements concatenation; e.g., +$$ \hbox{\verb|"abc" & "de"|} $$ +produces the string \verb|"abcde"|. The {\tt +length}\index{length?\texttt{length}}\label{DlengthString} operator +returns the number of characters in a string if the argument is a +\tdescr{string primary}; e.g., +$$ \hbox{\verb|length "abcde"|} $$ +returns \verb|5|. Another application of the {\tt length} operator is +discussed on p.\ \pageref{Dlength}. For substring construction, the +\tdescr{of operator} {\tt substring}\index{substring +of?\texttt{substring of}}\label{Dsubstr} is used like this: +$$ {\tt substring}\, \descr{pair expression} \,{\tt of}\, \descr{string primary} $$ +The \tdescr{pair expression} determines what part of the string to +select. For this purpose, the string is indexed\index{indexing} so that +integer positions fall {\em between\/} characters. Pretend the string +is written on a piece of graph paper so that the first character +occupies $x$~coordinates between zero and one and the next character +covers the range $1\le x\le2$, etc. Thus the string \verb|"abcde"| +should be thought of like this +$$ \includegraphics{mpman-14.mps} $$ +and {\tt substring (2,4) of "abcde"} is {\tt "cd"}. This takes a little +getting used to but it tends to avoid annoying ``off by one'' errors. + +Some operators take no arguments at all. An example of what +Figure~\ref{syexpr} calls a \tdescr{nullary op} is {\tt +nullpicture}\index{nullpicture?\texttt{nullpicture}}\label{Dnlpic} which +returns a completely blank picture. + +The basic syntax in Figure~\ref{syexpr} only covers aspects of the +expression syntax that are relatively type-independent. For instance, +the complicated path syntax given in Figure~\ref{sypath} gives +alternative rules for constructing a \tdescr{path expression}. An +additional rule\index{path knot?\tdescr{path knot}} +$$ \descr{path knot} \rightarrow \descr{pair tertiary} \;|\; \descr{path tertiary} +$$ +explains the meaning of \tdescr{path knot} in Figure~\ref{sypath}. This means +that the path expression +$$ \hbox{\verb|z1+(1,1){right}..z2|} $$ +does not need parentheses around {\tt z1+(1,1)}. + +\subsection{Fractions, Mediation, and Unary Operators} + +Mediation\index{mediation} expressions do not appear in the basic expression +syntax of Figure~\ref{syexpr}. Mediation expressions are parsed at the +\tdescr{primary} level, so the general rule for constructing them is +$$ \descr{primary} \rightarrow + \descr{numeric atom} \hbox{\tt [} \descr{expression} + \hbox{\tt ,} \descr{expression} \hbox{\tt ]} +$$ +where each \tdescr{expression} can be of type numeric, pair, or color. +The \tdescr{numeric atom}\index{numeric atom?\tdescr{numeric atom}} in a +mediation expression is an extra simple type of \tdescr{numeric primary} +as shown in Figure~\ref{synprim}. The meaning of all this is that the +initial parameter in a mediation expression needs to be parenthesized +when it is not just a variable, a positive number, or a positive +fraction. For example,\index{parsing irregularities} +$$ \hbox{\tt -1[a,b]} \quad {\rm and}\quad \hbox{\tt (-1)[a,b]} $$ +are very different: the former is $-b$ since it is equivalent to +{\tt -(1[a,b])}; the latter is $a-(b-a)$ or $2a-b$. + +\begin{figure}[htp] +\begin{ctabbing} +$\tt \descr{numeric primary} \rightarrow \descr{numeric atom}$\\ +$\tt \qquad \;|\; \descr{numeric atom}\hbox{\tt [} + \descr{numeric expression}\hbox{\tt ,}\descr{numeric expression}\hbox{\tt ]}$\\ +$\tt \qquad \;|\; \descr{of operator} \descr{expression} of \descr{primary}$\\ +$\tt \qquad \;|\; \descr{unary op} \descr{primary}$\\ +$\tt \descr{numeric atom} \rightarrow \descr{numeric variable}$\\ +$\tt \qquad \;|\; \descr{number or fraction}$\\ +$\tt \qquad \;|\; \hbox{\tt (}\descr{numeric expression}\hbox{\tt )}$\\ +$\tt \qquad \;|\; \descr{numeric nullary op}$\\ +$\tt \descr{number or fraction} \rightarrow \descr{number} + \hbox{\tt /}\descr{number}$\\ +$\tt \qquad \;|\; \descr{number not followed by + `$\hbox{\tt /}\descr{number}$'}$ +\end{ctabbing} +\caption{Syntax rules for numeric primaries} +\label{synprim} +\end{figure} + +A noteworthy feature of the syntax rules in Figure~\ref{synprim} is that +the {\tt /}\index{fractions} operator binds most tightly when its +operands are numbers. Thus {\tt 2/3} is a \tdescr{numeric +atom}\index{numeric atom?\tdescr{numeric atom}}\index{parsing +irregularities} while {\tt (1+1)/3} is only a \tdescr{numeric +secondary}. Applying a \tdescr{unary op} such as {\tt +sqrt}\index{sqrt?\texttt{sqrt}}\label{Dsqrt} makes the difference clear: +$$ \hbox{\tt sqrt 2/3} $$ +means $\sqrt{2\over3}$ while +$$ \hbox{\tt sqrt(1+1)/3} $$ +means $\sqrt 2/3$. Operators such as {\tt sqrt} can be written in +standard functional notation, but it is often unnecessary to +parenthesize the argument. This applies to any function that is parsed +as a \tdescr{unary op}. For instance {\tt +abs(x)}\index{abs?\texttt{abs}}\label{Dabs} and {\tt abs x} both compute +the absolute value of {\tt x}. The same holds for the {\tt +round}\index{round?\texttt{round}}\label{Dround}, {\tt +floor}\index{floor?\texttt{floor}}\label{Dfloor}, {\tt +ceiling}\index{ceiling?\texttt{ceiling}}\label{Dceil}, {\tt +sind}\index{sind?\texttt{sind}}\label{Dsind}, and {\tt +cosd}\index{cosd?\texttt{cosd}}\label{Dcosd} functions. The last two of +these compute trigonometric functions of angles in degrees. + +Not all unary operators take numeric arguments and return numeric +results. For instance, the {\tt abs}\index{abs?\texttt{abs}} operator +can be applied to a pair to compute the Euclidean length of a vector. +Applying the {\tt +unitvector}\index{unitvector?\texttt{unitvector}}\label{Duvec} operator +to a pair produces the same pair rescaled so that its Euclidean length +is~1. The {\tt decimal}\index{decimal?\texttt{decimal}}\label{Ddecop} +operator takes a number and returns the string representation. The {\tt +angle}\index{angle?\texttt{angle}}\label{Dangle} operator takes a pair +and computes the two-argument arctangent; i.e., {\tt angle} is the +inverse of the {\tt dir} operator that was discussed in +Section~\ref{tenscurl}. There is also an operator {\tt +cycle}\index{cycle?\texttt{cycle}}\label{Dcycop} that takes a +\tdescr{path primary} and returns a boolean result indicating whether +the path is a closed curve. + +There is a whole class of other operators that classify expressions and +return boolean results. A type name such as {\tt +pair}\index{pair?\texttt{pair}} can operate on any type of +\tdescr{primary} and return a boolean result indicating whether the +argument is a {\tt pair}\label{Dpairop}. Similarly, each of the +following can be used as a unary operator: +{\tt numeric}\index{numeric?\texttt{numeric}}\label{Dnumop}, +{\tt boolean}\index{boolean?\texttt{boolean}}\label{Dboolop}, +{\tt cmykcolor}\index{cmykcolor?\texttt{cmykcolor}}\label{Dccolrop}, +{\tt color}\index{color?\texttt{color}}\label{Dcolrop}, +{\tt string}\index{string?\texttt{string}}\label{Dstrgop}, +{\tt transform}\index{transform?\texttt{transform}}\label{Dtrnfop}, +{\tt path}\index{path?\texttt{path}}\label{Dpathop}, +{\tt pen}\index{pen?\texttt{pen}}\label{Dpenop}, +{\tt picture}\index{picture?\texttt{picture}}\label{Dpictop}, and +{\tt rgbcolor}\index{rgbcolor?\texttt{rgbcolor}}\label{Drcolrop}. +Besides just +testing the type of a \tdescr{primary}, you can use the {\tt +known}\index{known?\texttt{known}}\label{Dknown} and {\tt +unknown}\index{unknown?\texttt{unknown}}\label{Dunknwn} operators to +test if it has a completely known value. + +Even a number can behave like an operator in some contexts. This refers +to the trick that allows {\tt 3x}\index{multiplication, implicit} and +{\tt 3cm} as alternatives to {\tt 3*x} and {\tt 3*cm}. The rule is that +a \tdescr{number or fraction} that is not followed by {\tt +}, {\tt -}, +or another \tdescr{number or fraction} can serve as a \tdescr{primary +binop}. Thus {\tt 2/3x}\index{parsing irregularities} is two thirds of +{\tt x} but {\tt (2)/3x} is $2\over3x$ and {\tt 3 3} is illegal. + +There are also operators for extracting numeric subfields from pairs, +colors, cmykcolors, and even transforms. If {\tt p} is a \tdescr{pair +primary}, {\tt xpart p}\index{xpart?\texttt{xpart}}\label{Dxprt} and +{\tt ypart p}\index{ypart?\texttt{ypart}}\label{Dyprt} extract its components so that +$$ \hbox{\tt (xpart p, ypart p)} $$ is equivalent to~{\tt p} even if +{\tt p} is an unknown pair that is being used in a linear equation. +Similarly, a color {\tt c} is equivalent +to\index{redpart?\texttt{redpart}}% +\index{greenpart?\texttt{greenpart}}% +\index{bluepart?\texttt{bluepart}}\label{Drgbprt} +$$ \hbox{\tt (redpart c, greenpart c, bluepart c)}. $$ +For a cmykcolor {\tt c}, the components are% +\index{cyanpart?\texttt{cyanpart}}% +\index{magentapart?\texttt{magentapart}}% +\index{yellowpart?\texttt{yellowpart}}% +\index{blackpart?\texttt{blackpart}}\label{Dcmykprt} +$$ \hbox{\tt (cyanpart c, magentapart c, yellowpart c, blackpart c)} $$ +and for a greyscale color {\tt c}, there is only one component% +\index{greypart?\texttt{greypart}}\label{Dgreyprt}% +$$ \hbox{\tt greypart c}. $$ +All color component operators are discussed in more detail in +section~\ref{piccomp}. Part specifiers for transforms are discussed +in section~\ref{transsec}. + + +\section{Variables} +\label{vars} + +MetaPost allows compound variable names such as {z.a}, {\tt x2r}, {\tt y2r}, +and {\tt z2r}, where {\tt z2r} means {\tt (x2r,y2r)} and {\tt z.a} means +{\tt (x.a,y.a)}. In fact there is a broad class of suffixes such that +{\tt z}\tdescr{suffix}\index{suffix?\tdescr{suffix}} means +$$ (x\descr{suffix},\, y\descr{suffix}). $$ +Since a \tdescr{suffix} is composed of tokens, it is best to begin with a few +comments about tokens. + +\subsection{Tokens} + +A MetaPost input file is treated as a sequence of numbers, string +constants, and symbolic tokens\index{tokens}\index{tokens!symbolic}. A +number consists of a sequence of digits possibly containing a decimal +point. Technically, the minus sign in front of a negative number is a +separate token. Since MetaPost uses fixed point +arithmetic\index{arithmetic}, it does not understand exponential +notation such as {\tt 6.02E23}. MetaPost would interpret this as the +number 6.02, followed by the symbolic token {\tt E}, followed by the +number~23. + +Anything between a pair of double quotes {\tt "} is a +string constant\index{string constants}. It is +illegal for a string constant to start on one line and end on a later line. +Nor can a string constant contain double quotes {\tt "} or anything other than +printable ASCII characters. + +Everything in a line of input other than numbers and string constants is broken +into symbolic tokens\index{tokens!symbolic}. A symbolic token is a sequence of +one or more similar characters, where characters are ``similar'' if they occur +on the same row of Table~\ref{classes}. + +\begin{table} +$$\begin{tabular}{c} +\verb|ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz|\\ +{\tt :<=>|}\\ +\verb|#&@$|\\ +\verb|/*\|\\ +{\tt +-}\\ +{\tt !?}\\ +{\tt '`}\\ +\verb|^~|\\ +\verb|{}|\\ +{\tt [}\\ +{\tt ]}\\ +\end{tabular} +$$ +\caption{Character classes for tokenization} +\label{classes} +\end{table} + +Thus \verb|A_alpha| and {\tt +-+} are symbolic tokens but {\tt !=} is +interpreted as two tokens and {\tt x34} is a symbolic token followed by +a number. Since the brackets {\tt [} and {\tt ]} are listed on lines by +themselves, the only symbolic tokens involving them are {\tt [}, {\tt +[[}, {\tt [[[}, etc.\ and {\tt ]}, {\tt ]]}, etc. + +Some characters are not listed in Table~\ref{classes} because they need +special treatment. The four characters {\tt ,;()} are ``loners'': each +comma, semicolon, or parenthesis is a separate token even when they +occur consecutively. Thus {\tt (())} is four tokens, not one or two. +The percent sign is very special because it introduces +comments\index{\%?\texttt{\%}!comment}\index{comments}. The percent +sign and everything after it up to the end of the line are ignored. + +Another special character is the period. Two or more periods +together form a symbolic token, but a single period is ignored, and a period +preceded or followed by digits is part of a number Thus {\tt ..} +and {\tt ...} are symbolic tokens while {\tt a.b} is just two tokens {\tt a} +and {\tt b}. It conventional to use periods to separate tokens in this fashion +when naming a variable that is more than one token long. + +\subsection{Variable Declarations} +\label{vardecl} + +A variable name is a symbolic token or a sequence of symbolic tokens. +Most symbolic tokens are legitimate variable names, but anything with a +predefined meaning like {\tt draw}, {\tt +}, or {\tt ..} is disallowed; +i.e., variable names cannot be macros or MetaPost primitives. This +minor restriction allows an amazingly broad class of variable names: +{\tt alpha}, \verb|==>|, \verb|@&#$&|, and \verb|~~| are all legitimate +variable names. Such symbolic tokens without special meanings are +called {\em tags}\index{tags}. + +A variable name can be a sequence of tags like {\tt f.bot} or {\tt +f.top}. The idea is to provide some of the functionality of Pascal +records or C structures. It is also possible to simulate arrays by +using variable names that contain numbers as well as symbolic tokens. +For example, the variable name {\tt x2r} consists of the tag {\tt x}, +the number 2, and the tag~{\tt r}. There can also be variables named +{\tt x3r} and even {\tt x3.14r}. These variables can be treated as an +array\index{arrays} via constructions like {\tt x[i]r}, where {\tt i} +has an appropriate numeric value. The overall syntax for variable names +is shown in Figure~\ref{syvar}. + +\begin{figure}[htp] +\begin{ctabbing} +$\tt \descr{variable} \rightarrow \descr{tag}\descr{suffix}$\\ +$\tt \descr{suffix} \rightarrow \descr{empty} \;|\; + \descr{suffix}\descr{subscript} \;|\; \descr{suffix}\descr{tag}$\\ +$\tt \descr{subscript} \rightarrow \descr{number} \;|\; + \hbox{\tt [}\descr{numeric expression}\hbox{\tt ]}$ +\end{ctabbing} +\caption{The syntax for variable names.} +\index{suffix?\tdescr{suffix}}\index{subscript?\tdescr{subscript}} +\label{syvar} +\end{figure} + +Variables like {\tt x2} and {\tt y2} take on numeric values by default, so we +can use the fact that {\tt z}\tdescr{suffix} is an abbreviation for\index{z convention?{\tt z} convention}\label{Dzconv} +$$ (x\descr{suffix},\, y\descr{suffix}) $$ +to generate pair-valued variables when needed. It turns out that the +{\tt beginfig}\index{beginfig?\texttt{beginfig}} macro wipes out +pre-existing values variables that begin with the tags {\tt x} or {\tt +y} so that {\tt beginfig} \ldots\ {\tt endfig} blocks do not interfere +with each other when this naming scheme is used. In other words, +variables that start with {\tt x}, {\tt y}, {\tt z} are +local\index{variables!local}\index{locality} to the figure they are used +in. General mechanisms for making variables local will be discussed in +Section~\ref{grsec}. + +Type declarations\index{declarations}\index{type declarations} +make it possible to use almost any naming scheme while still +wiping out any previous value that might cause interference. For example, the +declaration +$$ \hbox{\tt pair pp, a.b;} $$ +makes {\tt pp} and {\tt a.b} unknown pairs. Such a declaration is not +strictly local since {\tt pp} and {\tt a.b} are not automatically +restored to their previous values at the end of the current figure. Of +course, they are restored to unknown pairs if the declaration is +repeated. + +Declarations work the same way for any of the other nine types: numeric, +path, transform, color, cmykcolor, string, boolean, picture, and pen. The +only restriction is that you cannot give explicit numeric subscripts in +a variable declaration. Do not give the illegal declaration +$$ \hbox{\tt numeric q1, q2, q3;} $$ +use the generic subscript\index{subscript!generic} symbol +{\tt []}\index{arrays}\index{[]?\texttt{[]}!array} +instead, to declare the whole array: +$$ \hbox{\tt numeric q[];} $$ +You can also declare ``multidimensional'' arrays\index{arrays!multidimensional}. +After the declaration +$$ \hbox{\tt path p[]q[], pq[][];} $$ +{\tt p2q3} and {\tt pq1.4 5} are both paths. + +Internal\index{internal variables}\index{variables!internal} variables +like {\tt tracingonline} cannot be declared in the normal fashion. All +the internal variables discussed in this manual are predefined and do +not have to be declared at all, but there is a way to declare that a +variable should behave like a newly-created internal variable. The +declaration is {\tt + newinternal}\index{newinternal?\texttt{newinternal}}\label{Dnewint} +followed by an optional type specifier \texttt{numeric}\index{internal + variables!\texttt{numeric}}\index{variables!internal!\texttt{numeric}} +or \texttt{string}\index{internal + variables!\texttt{string}}\index{variables!internal!\texttt{string}} +and a list of symbolic tokens. For example, +$$\begin{verbatim} +newinternal numeric n, m; +newinternal string s, t; +newinternal num; +\end{verbatim} +$$ +are valid declarations that declare three internal numeric variables +\texttt{n}, \texttt{m}, and~\texttt{num} and two internal string +variables \texttt{s} and~\texttt{t}. + +Internal variables always have known values, and these values can only +be changed by using the assignment\index{assignment} operator +{\tt:=}\index{:=?\texttt{:=}}. Internal numeric variables are initially +zero and internal string variables are initially the empty +string~\verb|""|, except that the Plain\index{Plain macros} macro +package gives some of the variables different initial values. (The +Plain macros are normally preloaded automatically as explained in +Section~\ref{intro}.) + +Internal string variables have been introduced in MetaPost +version~1.200. For backwards compatibility, if the type specifier is +missing, internal variables default to a \texttt{numeric}\index{internal + variables!\texttt{numeric}}\index{variables!internal!\texttt{numeric}} +type, as in the last example. The declarations \texttt{newinternal + numeric;} and \texttt{newinternal string;} are invalid and throw an +error. + + +\section{Integrating Text and Graphics} +\label{text} + +MetaPost has a number of features for including labels and other +text\index{text and graphics} in the figures it generates. The simplest +way to do this is to use the {\tt +label}\index{label?\texttt{label}}\label{Dlabel} statement\index{label +suffix?\tdescr{label suffix}} +$$ {\tt label}\descr{label suffix} \hbox{\tt (} + \descr{string or picture expression} \hbox{\tt,}\, \descr{pair expression} + \hbox{\tt );} +$$ +The \tdescr{string or picture expression} gives the label and the +\tdescr{pair expression} says where to put it. The \tdescr{label +suffix} can be \tdescr{empty} in which case the label is just centered +on the given coordinates. If you are labeling some feature of a diagram +you probably want to offset the label slightly to avoid overlapping. +This is illustrated in Figure~\ref{fig16} where the {\tt "a"} label is +placed above the midpoint of the line it refers to and the {\tt "b"} +label is to the left of the midpoint of its line. This is achieved by +using {\tt label.top}\index{top?\texttt{top}} for the {\tt "a"} label +and {\tt label.lft}\index{lft?\texttt{lft}} for the {\tt "b"} label as +shown in the figure. The \tdescr{label suffix} specifies the position +of the label relative to the specified coordinates. The complete set of +possibilities is\index{rt?\texttt{rt}}\index{bot?\texttt{bot}}% +\index{ulft?\texttt{ulft}}\index{urt?\texttt{urt}}\index{llft?\texttt{llft}}\index{lrt?\texttt{lrt}} +$$ \tt \descr{label suffix} \rightarrow + \descr{empty} \;|\; lft \;|\; rt \;|\; top \;|\; bot \;|\; + ulft \;|\;urt \;|\; llft \;|\; lrt +$$ +where {\tt lft} and {\tt rt} mean left and right and {\tt llft}, {\tt +ulft}, etc.\ mean lower left, upper left, etc. The actual amount by +which the label is offset in whatever direction is determined by the +internal variable\index{internal variables}\index{variables!internal} +{\tt +labeloffset}\index{labeloffset?\texttt{labeloffset}}\label{Dlaboff}. + +\begin{figure}[htp] +$$ +\begin{verbatim} +beginfig(17); +a=.7in; b=.5in; +z0=(0,0); +z1=-z3=(a,0); +z2=-z4=(0,b); +draw z1..z2..z3..z4..cycle; +draw z1--z0--z2; +label.top("a", .5[z0,z1]); +label.lft("b", .5[z0,z2]); +dotlabel.bot("(0,0)", z0); +endfig; +\end{verbatim} +\qquad \mathcenter{\includegraphics{mpman-17.mps}} +$$ +\caption{MetaPost code and the resulting output} +\label{fig16} +\end{figure} + +Figure~\ref{fig16} also illustrates the +{\tt dotlabel}\index{dotlabel?\texttt{dotlabel}}\label{Ddotlab} +statement. This is effectively +like a {\tt label} statement followed by a statement drawing a dot at +the indicated coordinates. For example +$$ \hbox{\tt dotlabel.bot("(0,0)", z0)} $$ +places a dot at {\tt z0} and then puts the label ``(0,0)'' just below +the dot. The diameter of the dot drawn by the {\tt dotlabel} statement +is determined by the value of the internal variable {\tt + dotlabeldiam}\index{dotlabeldiam?\texttt{dotlabeldiam}}\label{Ddotlabdiam}. +Default value is 3bp. + +Another alternative is the macro +{\tt thelabel}\index{thelabel?\texttt{thelabel}}\label{Dthelab}. This has +the same syntax as the {\tt label} and {\tt dotlabel} statements except that it +returns the label as a \tdescr{picture primary} instead of actually drawing it. +Thus +$$ \hbox{\tt label.bot("(0,0)", z0)} $$ +is equivalent to +$$ \hbox{\tt draw thelabel.bot("(0,0)", z0)} $$ + +For simple applications of labeled figures, you can normally get by with +just {\tt label} and {\tt dotlabel}. In fact, you may be able to use a +short form of the {\tt dotlabel} statement that saves a lot of typing +when you have many points {\tt z0}, {\tt z1}, {\tt z.a}, {\tt z.b}, +etc.\ and you want to use the {\tt z} suffixes as labels. The +statement\index{dotlabels?\texttt{dotlabels}}\label{Ddotlbs} +$$ \hbox{\tt dotlabels.rt(0, 1, a);} $$ +is equivalent to +$$ \hbox{\tt dotlabel.rt("0",z0); dotlabel.rt("1",z1); dotlabel.rt("a",z.a);} $$ +Thus the argument to {\tt dotlabels} is a list of suffixes for which {\tt z} +variables are known, and the \tdescr{label suffix} given with {\tt dotlabels} +is used to position all the labels. + +There is also a {\tt +labels}\index{labels?\texttt{labels}}\label{Dlabels} statement that is +analogous to {\tt dotlabels} but its use is discouraged because it +presents compatibility problems with \MF\index{metafont?\MF}. Some +versions of the preloaded Plain\index{Plain macros} macro package define +{\tt labels} to be synonymous with {\tt dotlabels}. + +For labeling statements such as {\tt label} and {\tt dotlabel} that use +a string expression for the label text, the string gets typeset in a +default font as determined by the string variable {\tt +defaultfont}\index{defaultfont?\texttt{defaultfont}}\label{Ddffont}. +The initial value of {\tt defaultfont} is likely to be {\tt "cmr10"}, +but it can be changed to a different font name by giving an assignment +such as +$$ \hbox{\tt defaultfont:="ptmr8r"} $$ +\ttt{ptmr8r} is a typical way to refer to the Times-Roman font in \TeX. +The discussion of font names on p.\ \pageref{fontname} explains further. + +There is also a numeric quantity called +{\tt defaultscale}\index{defaultscale?\texttt{defaultscale}}\label{Ddfscale} +that determines the type size. +When {\tt default\-scale} is 1, you get the ``normal size'' which is +usually 10 point, but this can also be changed. For instance +$$ \hbox{\tt defaultscale := 1.2} $$ +makes labels come out twenty percent larger. If you do not know the +normal size and you want to be sure the text comes out at some specific +size, say 12 points, you can use the {\tt +fontsize}\index{fontsize?\texttt{fontsize}}\label{Dfntsiz} operator to +determine the normal size: e.g., +$$ \hbox{\tt defaultscale := 12pt/fontsize defaultfont;} $$ + +\label{fontname} +When you change {\tt defaultfont}, the new font name should be something +that \TeX\ would understand since MetaPost gets height and width +information by reading a {\tt tfm}\index{tfm file?{\tt tfm} +file}\index{files!tfm?{\tt tfm}} file. (This is explained in {\sl The +\TeX book\/} \cite{kn:a}.) It should be possible to use built-in +PostScript\index{PostScript!fonts} fonts, but the names for +them are system-dependent. Some typical ones are {\tt ptmr8r} for +Times-Roman\index{Times-Roman}, \ttt{pplr8r} for Palatino\index{Palatino}, +and \ttt{phvr} for Helvetica\index{Helvetica}. The Fontname document, +available at \url{http://tug.org/fontname}, has much more information +about font names and \TeX. A \TeX\index{TeX?\TeX!fonts} font such +as {\tt cmr10} is a little dangerous because it does not have a space +character or certain ASCII symbols. + +MetaPost does not use the ligatures\index{ligatures} and +kerning\index{kerning} information that comes with a \TeX\ font. +Further, MetaPost itself does not interpret virtual fonts. + + +\subsection{Typesetting Your Labels} + +\label{Dbtex} +\index{labels, typesetting} + +\TeX\index{TeX?\TeX} may be used to format complex labels. +If you say\index{btex?\texttt{btex}}\index{etex?\texttt{etex}} +$$ {\tt btex}\, \descr{typesetting commands}\, {\tt etex} $$ +in a MetaPost input file, the \tdescr{typesetting commands} get processed by +\TeX\ and translated into a picture expression +(actually a \tdescr{picture primary}) that can be used in a {\tt label} +or {\tt dotlabel} statement. Any spaces after {\tt btex} or before {\tt etex} +are ignored. For instance, the statement +$$ \hbox{\verb|label.lrt(btex $\sqrt x$ etex, (3,sqrt 3)*u)|} $$ +in Figure~\ref{fig17} places the label $\sqrt x$ at the lower right of the +point {\tt (3,sqrt 3)*u}. + +\begin{figure}[htp] +$$ +\begin{verbatim} +beginfig(18); +numeric u; +u = 1cm; +draw (0,2u)--(0,0)--(4u,0); +pickup pencircle scaled 1pt; +draw (0,0){up} + for i=1 upto 8: ..(i/2,sqrt(i/2))*u endfor; +label.lrt(btex $\sqrt x$ etex, (3,sqrt 3)*u); +label.bot(btex $x$ etex, (2u,0)); +label.lft(btex $y$ etex, (0,u)); +endfig; +\end{verbatim} +\qquad \mathcenter{\includegraphics{mpman-18.mps}} +$$ +\caption{Arbitrary \TeX\ as labels} +\label{fig17} +\end{figure} + +Figure~\ref{fig18} illustrates some of the more complicated things that can +be done with labels. Since the result of {\tt btex} \ldots {\tt etex} is +a picture, it can be operated on like a picture. In particular, it is possible +to apply transformations to pictures. We have not discussed the syntax for +this yet, but a \tdescr{picture secondary} +can be\index{rotated text}\index{rotated?\texttt{rotated}} +$$ \descr{picture secondary}\, {\tt rotated}\, \descr{numeric primary} $$ +This is used in Figure~\ref{fig18} to rotate the label ``$y$ axis'' so that +it runs vertically. + +\begin{figure}[htp] +$$ +\begin{verbatim} +beginfig(19); +numeric ux, uy; +120ux=1.2in; 4uy=2.4in; +draw (0,4uy)--(0,0)--(120ux,0); +pickup pencircle scaled 1pt; +draw (0,uy){right} + for ix=1 upto 8: + ..(15ix*ux, uy*2/(1+cosd 15ix)) + endfor; +label.bot(btex $x$ axis etex, (60ux,0)); +label.lft(btex $y$ axis etex rotated 90, + (0,2uy)); +label.lft( + btex $\displaystyle y={2\over1+\cos x}$ etex, + (120ux, 4uy)); +endfig; +\end{verbatim} +\qquad \mathcenter{\includegraphics{mpman-19.mps}} +$$ +\caption{\TeX\ labels with display math, and rotated by MetaPost} +\label{fig18} +\end{figure} + +Another complication in Figure~\ref{fig18} is the use of the displayed equation +$$y={2\over 1+\cos x}$$ +as a label. It would be more natural to code this as +$$ \hbox{\verb|$$y={2\over 1+\cos x}$$|} $$ +but this would not work because +\TeX\ typesets the labels in ``horizontal mode.'' + +For a way to typeset \emph{variable} text as labels, see the +\texttt{TEX} utility routine described on p.\ \pageref{dTEX}. + +Here is how \TeX\ material gets translated into a form MetaPost +understands: MetaPost stores all {\tt btex}\index{btex?\texttt{btex}} +\ldots\ {\tt etex}\index{etex?\texttt{etex}} blocks in a temporary +file and then runs \TeX\ on that file. If the environment variable +\ttindex{MPTEXPRE} is set to the name of an existing file, its content +will be prepended to the output file for processing by \TeX. You can +use this to include \LaTeX\ preambles, for instance. The \ttt{TEX} +macro described on p.\ \pageref{dTEX} provides another way to handle +this. + +Once the \TeX\ run is finished, MetaPost translates the resulting +DVI\index{dvi file?{\tt dvi} file}\index{files!dvi?{\tt dvi}} file into +low level MetaPost commands that are then read instead of the {\tt btex} +\ldots\ {\tt etex} blocks. If the main file is {\tt fig.mp}, the +translated \TeX\ material is placed in a file named {\tt + fig.mpx}\index{mpx file?{\tt mpx} file}\index{files!mpx?{\tt mpx}}. + +The conversion normally runs silently without any user intervention but +it could fail, for instance if one of the {\tt btex} \ldots {\tt etex} +blocks contains an erroneous \TeX\index{TeX?\TeX!errors} command. In +that case, the \TeX\ input is saved in the file {\tt + mpxerr.tex}\index{mpxerr.tex?\texttt{mpxerr.tex}} and the \TeX\ error +messages appear in {\tt + mpxerr.log}\index{mpxerr.log?\texttt{mpxerr.log}}\index{log file?{\tt + log} file}\index{files!log?{\tt log}}. + +The DVI to MetaPost conversion route {\it does\/} understand virtual +fonts, so you can use your normal \TeX\ font switching commands inside +the label. + + +\label{Dmakempx} +In MetaPost versions before 1.100, the \TeX\ label preprocessing was +handled by an external program that was called upon automatically by +MetaPost. On Web2C-based systems, the preprocessor was normally named +\ttindex{makempx}, which called the utility \ttindex{mpto} for the +creation of the \TeX\ input file and the utility \texttt{dvitomp}\index{dvitomp?\texttt{dvitomp}} for +the conversion to low level MetaPost. In the current MetaPost version, +the work of this program is now done internally. However, if the +environment variable \ttindex{MPXCOMMAND} is set, the whole label +conversion mechanism will be delegated to the command given in that +variable. + + +\label{Dverbatimtex} +\TeX\ macro definitions or any other auxiliary \TeX\ commands can be +enclosed in a {\tt verbatimtex}\index{verbatimtex?\texttt{verbatimtex}} +\ldots\ {\tt etex}\index{etex?\texttt{etex}} block. The difference +between {\tt btex} and {\tt verbatimtex} is that the former generates a +picture expression while the latter only adds material for \TeX\ to +process. For instance, if you want \TeX\ to typeset labels using macros +defined in {\tt mymac.tex}, your MetaPost input file would look +something like this: +\begin{eqnarray*} +&& \verb|verbatimtex \input mymac etex|\\ +&& \verb|beginfig(1);|\\ +&& \qquad \dots\\ +&& \verb|label(btex|\, \descr{\TeX\ material using \hbox{\tt mymac.tex}}\, + \verb|etex, | \descr{some coordinates} \hbox{\tt );}\\ +&& \qquad \dots +\end{eqnarray*} + +\label{Dtroffmode} +On Unix\footnote{Unix is a registered trademark of Unix Systems +Laboratories.}\index{Unix} and other Web2C-based systems, the +option {\tt -troff} to MetaPost tells the preprocessor that {\tt btex} +$\ldots$ {\tt etex} and {\tt verbatimtex} $\ldots$ {\tt etex} blocks +are in troff\index{troff} instead of \TeX. When using this option, +MetaPost sets the internal variable +\ttindex{troffmode} to~1\index{prologues?\texttt{prologues}}. + +\label{Dprologues} +Setting \ttt{prologues} can be useful with \TeX, too, not just troff. +Here is some explanation: + +\begin{itemize} +\item In PostScript output mode, when \ttt{prologues} is 0, which is the default, the MetaPost +output files do not have embedded fonts. Fonts in the resulting +output will probably render as Courier\index{Courier} or +Times-Roman\index{Times-Roman}. + +In SVG mode, the text will probably render in a generic sans serif font. +There may very well be problems with the encoding of non-ASCII characters: +the font model of SVG is totally different from the model used by MetaPost. + +\item In PostScript output mode, when \ttt{prologues} is 1, the MetaPost output claims to be +``structured PostScript''\index{PostScript!structured} (EPSF\index{EPSF}), +but it is not completely conformant. This variant is kept for backward +compatibility with old (troff) documents, but its use is deprecated. +MetaPost sets \ttt{prologues} to~1 when the {\tt -troff} option is given +on the command line. + +A \ttt{prologues:=1} setting is currently ignored in SVG output +mode. The value is reserved for future use (possibly for mapping to +\ttt{font-family}, \ttt{font-weight}, etc. properties). + +\item In PostScript output mode, when \ttt{prologues} is 2, the +MetaPost output is EPSF and assumes +that the text comes from PostScript\index{PostScript!fonts} fonts +provided by the ``environment'', such as the document viewer or +embedded application using the output. MetaPost will attempt to +set up the font encodings correctly, based on \ttt{fontmapfile} and +\ttt{fontmapline} commands. + +A \ttt{prologues:=2} setting is currently ignored in SVG output mode. +The value is reserved for future use (possibly for external +\ttt{font-face} definitions). + +\item In PostScript output mode, when \ttt{prologues} is 3, the MetaPost output will be EPSF but +will contain the PostScript font(s) (or a subset) used based on the +\ttt{fontmapfile} and \ttt{fontmapline} commands. This value is useful +for generating stand-alone PostScript graphics. + +In SVG mode, the font glyphs are converted to path definitions that +are included at the top of the output file. + +\end{itemize} + +The correct setting for variable \texttt{prologues} depends on how +MetaPost graphics are post-processed. Here are recommendations for some +popular use-cases: + +\begin{description} + +\item[\normalfont\itshape Previewing:] Section~\ref{preview} discusses + previewing PostScript output. + +\item[\normalfont\itshape \TeX\ and dvips:] When including PostScript + figures into a \TeX\ document that is processed by \TeX\ and a DVI + output processer, e.g., dvips\index{dvips}, variable + \texttt{prologues} should \emph{not} be set to the value~1, unless the + used fonts are known to be resident in the PostScript interpreter. + Make sure that variable \texttt{prologues} is set to either~0 (font + inclusion handled by dvips, but without re-encoding support), 2 (font + inclusion by dvips, with font re-encoding if necessary), or~3 (font + inclusion and re-encoding by MetaPost). Value~3 is safest, but may + result in slightly larger output. + +\item[\normalfont\itshape pdf\TeX:] When generating PDF files with + pdf\TeX\ (and the mptopdf\index{mptopdf} bundle), variable + \texttt{prologues} is not relevant. + +\item[\normalfont\itshape PostScript in external applications:] Some + text\index{text processor} processors or graphics applications can + directly import EPSF files, while for others MetaPost's PostScript + output has to be converted to a different vector or even a bitmap + format first. In any case, as soon as PostScript graphics generated + by MetaPost are leaving the \TeX\ ecosystem, variable + \texttt{prologues} should be set to~3, so that all needed fonts are + embedded (as a subset). + +\item[\normalfont\itshape SVG output:] Converting font glyphs to paths + by setting variable \texttt{prologues} to~3 is currently the only + reliable way to export text objects to SVG. + +\item[\normalfont\itshape PNG output:] Variable \texttt{prologues} has + no effect in PNG output mode. + +\end{description} + +It is worth noting that the value of \ttt{prologues} has no effect on +\MF\ fonts in your MetaPost files, i.\,e., MetaPost never embeds such +fonts. Only output drivers, e.\,g., \ttt{dvips} or pdf\LaTeX\ will +handle those. + +The details on how to include PostScript figures in a paper +done in \TeX\ or troff are system-dependent. They can generally be found +in manual pages and other on-line documentation, but have a look at +section~\ref{mpimport} of this manual for some brief instructions that +in many cases should work. The manual for the +widely-used Dvips processor is in a file \ttt{dvips.texi}, included in +most distributions, and is available online at +\url{http://tug.org/texinfohtml/dvips.html}, among many other places and +formats. + +\subsection{Font Map Files} +\label{fontmap} + +If \ttt{prologues} is set to~2, any used fonts in the output file are +automatically re-encoded, and the encoding vector file specified in +the fontmap entry will be embedded in the output file. If +\ttt{prologues} is set to~3, MetaPost will also attempt to include +(a subset of) the used PostScript\index{PostScript!fonts} fonts. For +this to work, it needs to acquire font map information. + +The code is based on the font library used by pdf\TeX. Following in the +footsteps of pdf\TeX, there are two new associated primitives: +\ttindex{fontmapfile}\label{Dfontmapfile} and +\ttindex{fontmapline}\label{Dfontmapline}. Here is a simple example, +specifying the map file for Latin Modern fonts in YandY (\LaTeX\ LY1) +encoding: +\begin{center}\begin{tabular}{l} +\verb|prologues:=2;|\\ +\verb|fontmapfile "texnansi-lm.map";|\\ +\verb|beginfig(1);|\\ +\verb| draw "Helló, világ" infont "texnansi-lmr10";|\\ +\verb|endfig;| +\end{tabular}\end{center} + +Using \ttt{fontmapline}, you can specify font mapping information +inside the figure: +\begin{center}\begin{tabular}{l} +\verb|prologues:=2;|\\ +\verb|fontmapline "pplbo8r URWPalladioL-Bold "&ditto&|\\ +\verb| ".167 SlantFont"&ditto&" <8r.enc <uplb8a.pfb";|\\ +\verb|beginfig(1);|\\ +\verb| draw "Hello, world" infont "pplbo8r";|\\ +\verb|endfig;| +\end{tabular}\end{center} +This will attempt to reencode the PostScript font +URWPalladioL-Bold\index{URWPalladioL-Bold}\index{Palatino} +whose tfm file is pplbo8r.tfm. The encoding is found in the file +8r.enc, and will be included into the output file. + +If the same example was run with \ttt{prologues:=3}, MetaPost would +include a subset of the font that resides in uplb8a.pfb into the +output. In this case, the subset of the font is reorganized so that it +has the correct encoding internally, 8r.enc will not be embedded also. + +The argument to both commands has an optional flag character at the very +beginning. This optional flag has the same meaning as in pdf\TeX: +$$\begin{tabular}{|c|l|} \hline +\multicolumn1{|c|}{Option}& \multicolumn1{c|}{Meaning}\\ \hline + + & extend the font list, but ignore duplicates \\ + = & extend the font list, replacing duplicates \\ + $-$ & remove all matching fonts from the font list \\ +\hline +\end{tabular} +$$ +Without any option, the current list will be completely replaced. + +If \ttt{prologues} is set to two or three, yet there are no +\ttt{fontmapfile} statements, MetaPost will attempt to locate a +default map file, with a preference to read {\tt mpost.map}. If that +fails, it will also attempt either {\tt troff.map} or {\tt +pdftex.map}, depending on whether or not troff mode is enabled. If +\ttt{prologues} is set to~1, MetaPost attempts to read a file called +{\tt psfonts.map}, regardless of any {\tt fontmapfile} +statement. Again, this is for backward compatibility only. + + +\subsection{The \texttt{infont} Operator} +\label{Sinfont} + +Regardless of whether you use \TeX\ or troff, all the real work of +adding text to pictures is done by a MetaPost primitive operator called +{\tt infont}\index{infont?\texttt{infont}}. It is a \tdescr{primary + binop}\index{primary binop?\tdescr{primary binop}} that takes a +\tdescr{string secondary} as its left argument and a \tdescr{string + primary} as its right argument. The left argument is text, and the +right argument is a font name. The result of the operation is a +\tdescr{picture secondary}, which can then be transformed in various +ways. One possibility is enlargement by a given factor via the +syntax\index{scaled?\texttt{scaled}} +$$ \descr{picture secondary}\, \hbox{\tt scaled}\, \descr{numeric primary} $$ +Thus {\tt label("text",z0)} is equivalent to +$$ \hbox{\tt label("text" infont defaultfont scaled defaultscale, z0)} $$ + +If it is not convenient to use a string constant for the left argument of +{\tt infont}, you can use\index{char?\texttt{char}}\label{Dchar} +$$ {\tt char}\, \descr{numeric primary} $$ +to select a character based on its numeric position in the font. +Thus +$$ \hbox{\tt char(n+64) infont "ptmr8r"} $$ +is a picture containing character {\tt n+64} of the font \ttt{ptmr8r}, +which is a typical \TeX\ way to refer to Times-Roman. See p.\ +\pageref{fontname} for further discussion. + +Bare MetaPost does not do any kind of input reencoding, so when +you use {\tt infont} string for labels (instead of {\tt btex} \ldots\ +{\tt etex}), the string has to be specified in the font encoding. + + +\subsection{Measuring Text} +\label{meas} + +MetaPost makes readily available the physical dimensions\index{size} of +pictures generated by the {\tt infont} operator. There are unary +operators {\tt +llcorner}\index{llcorner?\texttt{llcorner}}\label{Dcornop}, {\tt +lrcorner}\index{lrcorner?\texttt{lrcorner}}, {\tt +urcorner}\index{urcorner?\texttt{urcorner}}, {\tt +ulcorner}\index{ulcorner?\texttt{ulcorner}}, and {\tt +center}\index{center?\texttt{center}}\label{Dcenter} that take a \tdescr{picture +primary} and return the corners of its ``bounding box'' as illustrated +in Figure~\ref{bbox}. The {\tt center} operator also accepts +\tdescr{path primary} and \tdescr{pen primary} operands. In MetaPost +Version 0.30 and higher, {\tt llcorner}, {\tt lrcorner}, etc. accept +all three argument types as well. + +The argument type restrictions on the corner operators are not very +important because their main purpose is to allow {\tt label} and {\tt +dotlabel} statements to center their text properly. The predefined +macro\index{bbox?\texttt{bbox}}\label{Dbbox} +$$ {\tt bbox}\, \descr{picture primary} $$ +finds a rectangular path that represents the bounding box of a given picture. +If {\tt p} is a picture, {\tt bbox p} is equivalent to +$$\begin{verbatim} +(llcorner p--lrcorner p--urcorner p--ulcorner p--cycle) +\end{verbatim} +$$ +except that it allows for a small amount of extra space around {\tt p} +as specified by the internal variable\index{internal +variables}\index{variables!internal} {\tt +bboxmargin}\index{bboxmargin?\texttt{bboxmargin}}\label{Dbbmargin}. + +\begin{figure}[htp] +$$ \includegraphics{mpman-20.mps} $$ +\caption{A bounding box and its corner points.} +\label{bbox} +\end{figure} + +Note that MetaPost computes the bounding box of a {\tt +btex}\index{btex?\texttt{btex}} \ldots\ {\tt +etex}\index{etex?\texttt{etex}} picture just the way +\TeX\index{TeX?\TeX} does. This is quite natural, but it has certain +implications in view of the fact that \TeX\ has features like +{\tt\string\strut}\index{strut?{\tt\string\strut}} and +{\tt\string\rlap}\index{rlap?{\tt\string\rlap}} that allow \TeX\ users +to lie about the dimensions of a box. + +When \TeX\ commands that lie about the dimensions of a box are +translated in to low-level MetaPost code, a {\tt +setbounds}\index{setbounds?\texttt{setbounds}}\label{Dsetbnd} statement +does the lying:\index{picture variable?\tdescr{picture variable}} +$$ {\tt setbounds}\, \descr{picture variable}\, {\tt to}\, \descr{path expression} +$$ +makes the \tdescr{picture variable} behave as if its bounding box were +the same as the given path. The path has to be a cycle, i.e., it must +be a closed path. To get the true bounding box of such a +picture, assign a positive value to the internal variable\index{internal +variables}\index{variables!internal} {\tt +truecorners}\index{truecorners?\texttt{truecorners}}\label{Dtruecorn}:\footnote{The +{\tt setbounds} and {\tt truecorners} features are only found in +MetaPost version 0.30 and higher.} i.e., +$$ \hbox{\verb|show urcorner btex $\bullet$\rlap{ A} etex|} $$ +produces ``\verb|>> (4.9813,6.8078)|'' while +$$ \hbox{\verb|truecorners:=1; show urcorner btex $\bullet$\rlap{ A} etex|} $$ +produces ``\verb|>> (15.7742,6.8078)|.'' + + +\section{Advanced Graphics} +\label{adv.gr} + +All the examples in the previous sections have been simple line drawings +with labels added. This section describes shading and tools for +generating not-so-simple line drawings. Shading is done with the {\tt +fill}\index{fill?\texttt{fill}}\label{Dfill} statement. In its simplest +form, the {\tt fill} statement requires a \tdescr{path expression} that +gives the boundary of the region to be filled. In the syntax +$$ {\tt fill}\, \descr{path expression} $$ +the argument should be a cyclic path, i.e., a path that describes a +closed curve via the \verb|..cycle| or \verb|--cycle| notation. For +example, the {\tt fill} statement in Figure~\ref{fig20} builds a closed +path by extending the roughly semicircular path~{\tt p}. This path has +a counter-clockwise orientation, but that does not matter because the +{\tt fill} statement uses PostScript's\index{PostScript} non-zero +winding\index{winding number} number rule\index{non-zero fill + rule}\index{fill rule!non-zero}\index{PostScript!fill + rule}~\cite{ad:red2}. + +\begin{figure}[htp] +$$ \begin{verbatim} +beginfig(21); +path p; +p = (-1cm,0)..(0,-1cm)..(1cm,0); +fill p{up}..(0,0){-1,-2}..{up}cycle; +draw p..(0,1cm)..cycle; +endfig; +\end{verbatim} +\qquad \mathcenter{\includegraphics{mpman-21.mps}} +$$ +\caption{MetaPost code and the corresponding output.} +\label{fig20} +\end{figure} + +The general {\tt fill} statement\index{withcolor?\texttt{withcolor}}\label{Dwithcolor} +$$ {\tt fill}\, \descr{path expression}\, + {\tt withcolor}\, \descr{color expression} +$$ +specifies a shade of gray or (if you have a color printer) some +rainbow color. The $\descr{color expression}$ can have five possible +values, mapping to four possible color models: + +$$ +\begin{tabular}{ll} +Actual input & Remapped meaning\\\hline +{\tt withcolor} $\descr{rgbcolor} c$ & withrgbcolor\index{withrgbcolor?\texttt{withrgbcolor}}\label{Dwithrgbcolor} $c$\\ +{\tt withcolor} $\descr{cmykcolor} c$ & withcmykcolor\index{withcmykcolor?\texttt{withcmykcolor}}\label{Dwithcmykcolor} $c$\\ +{\tt withcolor} $\descr{numeric} c$ & withgreyscale\index{withgreyscale?\texttt{withgreyscale}}\label{Dwithgreyscale} $c$\\ +{\tt withcolor} $\descr{false}$ & withoutcolor\index{withoutcolor?\texttt{withoutcolor}}\label{Dwithoutcolor} \\ +{\tt withcolor} $\descr{true}$ & $\descr{current default color model}$\\ +\end{tabular} +$$ + +For the specific color models, there are also: +$$ {\tt fill}\, \descr{path expression}\, + {\tt withrgbcolor}\, \descr{rgbcolor expression} +$$ +$$ {\tt fill}\, \descr{path expression}\, + {\tt withcmykcolor}\, \descr{cmykcolor expression} +$$ +$$ {\tt fill}\, \descr{path expression}\, + {\tt withgreyscale}\, \descr{numeric} +$$ +$$ {\tt fill}\, \descr{path expression}\, + {\tt withoutcolor} +$$ + +An image object cannot have more then one color model, the last +\ttt{withcolor}, \ttt{withrgbcolor}, \ttt{withcmykcolor}, +\ttt{withgreyscale} or \ttt{withoutcolor} specification sets the color +model for any particular object. + +The model \ttt{withoutcolor} needs a bit more explanation: selecting +this model means that MetaPost will not write a color selection +statement to the PostScript output file for this object. + +The `current default' color model can be set up using the internal +variable \ttindex{defaultcolormodel}\label{Ddefaultcolormodel}. +Table~\ref{dfltcmod} lists the valid values. +\begin{table} +\centering +\begin{tabular}{|c|l|} +\hline +Value & Color model\\\hline +1 & no model\\ +3 & greyscale\\ +5 & rgb (default)\\ +7 & cmyk\\ +\hline +\end{tabular} +\caption{Supported color models.} +\label{dfltcmod} +\end{table} + + +Figure~\ref{fig21} illustrates several applications of the fill command +to fill areas with shades of gray. The paths involved are intersecting +circles {\tt a} and {\tt b} and a path {\tt ab} that bounds the region +inside both circles. Circles {\tt a} and {\tt b} are derived from {\tt + fullcircle}. Path~{\tt ab} is then initialized using a predefined +macro {\tt buildcycle} that will be discussed shortly. + +\begin{figure}[htp] +$$ \begin{verbatim} +beginfig(22); +path a, b, aa, ab; +a = fullcircle scaled 2cm; +b = a shifted (0,1cm); +aa = halfcircle scaled 2cm; +ab = buildcycle(aa, b); +picture pa, pb; +pa = thelabel(btex $A$ etex, (0,-.5cm)); +pb = thelabel(btex $B$ etex, (0,1.5cm)); +fill a withcolor .7white; +fill b withcolor .7white; +fill ab withcolor .4white; +unfill bbox pa; +draw pa; +unfill bbox pb; +draw pb; +label.lft(btex $U$ etex, (-1cm,.5cm)); +draw bbox currentpicture; +endfig; +\end{verbatim} +\qquad \mathcenter{\includegraphics{mpman-22.mps}} +$$ +\caption{MetaPost code and the corresponding output.} +\index{fullcircle?\texttt{fullcircle}}\index{halfcircle?\texttt{halfcircle}}\index{buildcycle?\texttt{buildcycle}} +\label{fig21} +\end{figure} + +Filling circle {\tt a} with the light gray color {\tt .7white} and then +doing the same with circle {\tt b} doubly fills the region where the +disks overlap. The rule is that each {\tt fill} statement assigns the +given color to all points in the region covered, wiping out whatever was +there previously including lines and text as well as filled regions. +Thus it is important to give {\tt fill} commands in the right order. In +the above example, the overlap region gets the same color twice, leaving +it light gray after the first two {\tt fill} statements. The third fill +statement assigns the darker color {\tt .4white} to the overlap region. + +At this point the circles and the overlap region have their final colors +but there are no cutouts for the labels. The cutouts are achieved by +the {\tt unfill}\index{unfill?\texttt{unfill}}\label{Dunfill} statements +that effectively erase\index{erasing} the regions bounded by {\tt bbox +pa}\index{bbox?\texttt{bbox}} and {\tt bbox pb}. More precisely, {\tt +unfill} is shorthand for filling {\tt withcolor background}, where {\tt +background} is normally equal to {\tt white} as is appropriate for +printing on white paper. If necessary, you can assign a new color value +to {\tt +background}\index{background?\texttt{background}}\label{Dbground}. + +The labels need to be stored in pictures {\tt pa} and {\tt pb} to allow +for measuring their bounding box before actually drawing them. The +macro {\tt thelabel}\index{thelabel?\texttt{thelabel}} creates such +pictures and shifts them into position so that they are ready to draw. +Using the resulting pictures in {\tt draw} statements of the +form\index{draw?\texttt{draw}} +$$ {\tt draw}\, \descr{picture expression} $$ +adds them to {\tt currentpicture}\index{currentpicture?\texttt{currentpicture}} +so that they overwrite a portion of what has +already been drawn. In Figure~\ref{fig21} just the white rectangles produced by +{\tt unfill} get overwritten. + +\subsection{Building Cycles} +\label{buildcy} + +The {\tt buildcycle}\index{buildcycle?\texttt{buildcycle}} command +constructs paths for use with the {\tt fill} or {\tt unfill} macros. +When given two or more paths such as {\tt aa} and {\tt b}, the {\tt +buildcycle} macro tries to piece them together so as to form a cyclic +path. In this case path {\tt aa} is a semicircle that starts just to +the right of the intersection with path {\tt b}, then passes through +{\tt b} and ends just outside the circle on the left as shown in +Figure~\ref{fig22}a. + +Figure~\ref{fig22}b shows how {\tt buildcycle} forms a closed cycle from +the pieces of paths {\tt aa} and {\tt b}. The {\tt buildcycle} macro +detects the two intersections\index{intersections} labeled 1 and 2 in +Figure~\ref{fig22}b. Then it constructs the cyclic path shown in bold +in the figure by going forward along path {\tt aa} from intersection~1 +to intersection~2 and then forward around the counter-clockwise path +{\tt b} back to intersection~1. It turns out that {\tt buildcycle(a,b)} +would have produced the same result, but the reasoning behind this is a +little confusing. + + +\begin{figure}[htp] +$$ {\includegraphics{mpman-123.mps} \atop (a)} + \qquad {\includegraphics{mpman-223.mps} \atop (b)} +$$ +\caption[A demonstration of cycle building] + {(a)~The semicircular path~{\tt aa} + with a dashed line marking path {\tt b}; (b)~paths~{\tt aa} and {\tt b} + with the portions selected by {\tt buildcycle} shown by heavy lines.} +\label{fig22} +\end{figure} + +It is a easier to use the {\tt buildcycle} macro in situations like +Figure~\ref{fig23} where there are more than two path arguments and each +pair of consecutive paths has a unique intersection. For instance, the +line~{\tt q0.5} and the curve~{\tt p2} intersect only at point~$P$; and +the curve {\tt p2} and the line~{\tt q1.5} intersect only at point~$Q$. +In fact, each of the points $P$, $Q$, $R$, $S$ is a unique intersection, +and the result of\index{buildcycle?\texttt{buildcycle}} +$$ \hbox{\tt buildcycle(q0.5, p2, q1.5, p4)} $$ +takes {\tt q0.5} from $S$ to~$P$, then {\tt p2} from $P$ to~$Q$, then +{\tt q1.5} from $Q$ to~$R$, and finally {\tt p4} from $R$ back to~$S$. +An examination of the MetaPost code for Figure~\ref{fig23} reveals that +you have to go backwards along {\tt p2} in order to get from $P$ to~$Q$. +This works perfectly well as long as the +intersection\index{intersection} points are uniquely defined but it can +cause unexpected results when pairs of paths intersect more than once. + +\begin{figure}[htp] +$$ \begin{verbatim} +beginfig(24); +h=2in; w=2.7in; +path p[], q[], pp; +for i=2 upto 4: ii:=i**2; + p[i] = (w/ii,h){1,-ii}...(w/i,h/i)...(w,h/ii){ii,-1}; +endfor +q0.5 = (0,0)--(w,0.5h); +q1.5 = (0,0)--(w/1.5,h); +pp = buildcycle(q0.5, p2, q1.5, p4); +fill pp withcolor .7white; +z0=center pp; +picture lab; lab=thelabel(btex $f>0$ etex, z0); +unfill bbox lab; draw lab; +draw q0.5; draw p2; draw q1.5; draw p4; +dotlabel.top(btex $P$ etex, p2 intersectionpoint q0.5); +dotlabel.rt(btex $Q$ etex, p2 intersectionpoint q1.5); +dotlabel.lft(btex $R$ etex, p4 intersectionpoint q1.5); +dotlabel.bot(btex $S$ etex, p4 intersectionpoint q0.5); +endfig; +\end{verbatim} +\atop \mathcenter{\includegraphics{mpman-24.mps}} +$$ +\caption{MetaPost code and the corresponding output.} +\label{fig23} +\end{figure} + +The general rule for the {\tt buildcycle} macro is that +$$ \hbox{\tt buildcycle(}p_1\hbox{\tt,}\, p_2\hbox{\tt,}\, + p_3\hbox{\tt,}\, \ldots \hbox{\tt,} p_k \hbox{\tt )} +$$ +chooses the intersection between each $p_i$ and $p_{i+1}$ to be as late +as possible on $p_i$ and as early as possible on $p_{i+1}$. There is no +simple rule for resolving conflicts between these two goals, so you +should avoid cases where one intersection point occurs later on $p_i$ +and another intersection\index{intersection} point occurs earlier on +$p_{i+1}$. + +The preference for intersections as late as possible on $p_i$ and as +early as possible on $p_{i+1}$ leads to ambiguity resolution in favor of +forward-going subpaths. For cyclic paths such as path~{\tt b} in +Figure~\ref{fig22} ``early'' and ``late'' are relative to a start/finish +point which is where you get back to when you say ``{\tt ..cycle}''. +For the path~{\tt b}, this turns out to be the rightmost point on the +circle. + +A more direct way to deal with path intersections is via the +\tdescr{secondary binop}\index{secondary binop?\tdescr{secondary binop}} +{\tt +intersection\-point}\index{intersectionpoint?\texttt{intersectionpoint}}\label{Disecpt} +that finds the points $P$, $Q$, $R$, and~$S$ in Figure~\ref{fig23}. +This macro finds a point where two given paths intersect. If there is +more than one intersection point, it just chooses one; if there is no +intersection, the macro generates an error message. + +\subsection{Dealing with Paths Parametrically} + +The {\tt +intersectionpoint}\index{intersectionpoint?\texttt{intersectionpoint}} +macro is based on a primitive operation called {\tt +intersectiontimes}\index{intersectiontimes?\texttt{intersectiontimes}}\label{Disectt}. +This \tdescr{secondary binop} is one of several operations that deal +with paths parametrically. It locates an intersection between two paths +by giving the ``time'' parameter on each path. This refers to the +parameterization scheme from Section~\ref{curves} that described paths +as piecewise cubic curves $\bigl(X(t),Y(t)\bigr)$ where $t$ ranges from +zero to the number of curve segments. In other words, when a path is +specified as passing through a sequence of points, where $t=0$ at the +first point, then $t=1$ at the next, and $t=2$ at the next, etc. The +result of +$$ \hbox{\tt a intersectiontimes b} $$ +is $(-1,-1)$ if there is no intersection; otherwise you get +a pair $(t_a,t_b)$, where $t_a$ is a time on path {\tt a} when it intersects +path~{\tt b}, and $t_b$ is the corresponding time on path~{\tt b}. + +For example, suppose path~{\tt a} is denoted by the thin line in +Figure~\ref{fig24} and path~{\tt b} is denoted by the thicker line. If +the labels indicate time values on the paths, the pair of time values +computed by +$$ \hbox{\tt a intersectiontimes b} $$ +must be one of +$$ (0.25,1.77),\ (0.75,1.40), {\rm or}\ (2.58,0.24), $$ +depending on which of the three intersection points is chosen by the +MetaPost interpreter. The exact rules for choosing among multiple +intersection points are a little complicated, but it turns out that you +get the time values $(0.25,1.77)$ in this example. Smaller time values +are preferred over larger ones so that $(t_a,t_b)$ is preferred to +$(t'_a,t'_b)$ whenever $t_a<t'_a$ and $t_b<t'_b$. When no single +alternative minimizes both the $t_a$ and $t_b$ components the $t_a$ +component tends to get priority, but the rules get more complicated when +there are no integers between $t_a$ and $t'_a$\index{intersection}. +(For more details, see {\sl The \MF book} \cite[Chapter 14]{kn:c}). + +\begin{figure}[htp] +$$ \includegraphics{mpman-25.mps} $$ +\caption{Two intersecting paths with time values marked on each path.} +\label{fig24} +\end{figure} + +The {\tt intersectiontimes} operator is more flexible than {\tt +intersectionpoint} because there are a number of things that can be done +with time values on a path. One of the most important is just to ask +``where is path {\tt p} at time {\tt t}?'' The construction\index{point +of?\texttt{point of}}\label{Dpntof} +$$ {\tt point}\, \descr{numeric expression}\, {\tt of}\, \descr{path primary} $$ +answers this question. If the \tdescr{numeric expression} is less than +zero or greater than the time value assigned to the last point on the +path, the {\tt point of} construction normally yields an endpoint of the +path. Hence, it is common to use the predefined constant {\tt +infinity}\index{infinity?\texttt{infinity}}\label{Dinf} (equal to +4095.99998) as the \tdescr{numeric expression} in a {\tt point of} +construction when dealing with the end of a path. + +Such ``infinite'' time values do not work for a cyclic path, since time +values outside of the normal range can be handled by modular arithmetic +in that case; i.e., a cyclic path~{\tt p} through points $z_0$, $z_1$, +$z_2$, \ldots, $z_{n-1}$ has the normal parameter range $0\le t<n$, but +$$ \hbox{\tt point t of p} $$ +can be computed for any~$t$ by first reducing $t$ modulo~$n$. If the +modulus~$n$ is not readily +available,\index{length?\texttt{length}}\label{Dlength} +$$ {\tt length}\, \descr{path primary} $$ +gives the integer value of the upper limit of the normal time parameter +range for the specified path. + +MetaPost uses the same correspondence between time values and points on +a path to evaluate the {\tt +subpath}\index{subpath?\texttt{subpath}}\label{Dsubpth} operator. The +syntax for this operator is +$$ {\tt subpath}\, \descr{pair expression}\, {\tt of}\, \descr{path primary} $$ +If the value of the \tdescr{pair expression} is $(t_1,t_2)$ and the +\tdescr{path primary} is $p$, the result is a path that follows $p$ from +{\tt point $t_1$ of $p$} to {\tt point $t_2$ of $p$}. If $t_2<t_1$, the +subpath runs backwards along~$p$. + +An important operation based on the {\tt subpath} operator is the +\tdescr{tertiary binop}\index{tertiary binop?\tdescr{tertiary binop}} +{\tt cutbefore}\index{cutbefore?\texttt{cutbefore}}\label{Dcutb}. For +intersecting paths $p_1$ and $p_2$, +$$ p_1\ {\tt cutbefore}\ p_2 $$ +is equivalent to +$$ \hbox{\tt subpath (xpart($p_1$ intersectiontimes $p_2$), length $p_1$) of $p_1$} +$$ +except that it also sets the path variable {\tt +cuttings}\index{cuttings?\texttt{cuttings}}\label{Dcuttings} to the +portion of $p_1$ that gets cut off. In other words, {\tt cutbefore} +returns its first argument with the part before the intersection cut +off. With multiple intersections, it tries to cut off as little as +possible. If the paths do not intersect, {\tt cutbefore} returns its +first argument. + +There is also an analogous \tdescr{tertiary binop}\index{tertiary +binop?\tdescr{tertiary binop}} called {\tt +cutafter}\index{cutafter?\texttt{cutafter}}\label{Dcuta} that works by +applying {\tt cutbefore} with time reversed along its first argument. +Thus +$$ p_1\ {\tt cutafter}\ p_2 $$ +tries to cut off the part of $p_1$ after its last intersection with $p_2$. + +The control points of a path can be requested by the two operators +\index{precontrol of?\texttt{precontrol of}} +\index{postcontrol of?\texttt{postcontrol of}} +\label{Dprepostctrl} +\begin{eqnarray*} + {\tt precontrol}\, \descr{numeric expression}\, {\tt of}\, \descr{path primary},\\ + {\tt postcontrol}\, \descr{numeric expression}\, {\tt of}\, \descr{path primary}. +\end{eqnarray*} + +For integer time values~$t$, these operators return the control points +before and after a cardinal point of a path. A segment +$z_{t-1}\verb|..|z_t$ of a path~$p$ has therefore control points +$$ {\tt postcontrol}\ t-1\ {\tt of}\ p +$$ +and +$$ {\tt precontrol}\ t\ {\tt of}\ p. +$$ + +For decimal time values, {\tt precontrol of} returns the last control +point of sub-path $(0, t)$ and {\tt postcontrol of} returns the first +control point of sub-path $(t, \infty)$ of a path. In other words, the +control points at fractional time values correspond to a virtual +cardinal point inserted at the given time value without modifying path +shape. + +Another operator\index{direction of?\texttt{direction of}}\label{Ddirof} +$$ {\tt direction}\, \descr{numeric expression}\, {\tt of}\, \descr{path primary} +$$ +finds a vector in the direction of the \tdescr{path primary}. This is +defined for any time value analogously to the {\tt point of} +construction. The resulting direction vector has the correct +orientation and a somewhat arbitrary magnitude. Combining {\tt point +of} and {\tt direction of} constructions yields the equation for a +tangent line as illustrated in Figure~\ref{fig25}. + +\begin{figure}[htp] +$$ \begin{verbatim} +beginfig(26); +numeric scf, #, t[]; +3.2scf = 2.4in; +path fun; +# = .1; % Keep the function single-valued +fun = ((0,-1#)..(1,.5#){right}..(1.9,.2#){right}..{curl .1}(3.2,2#)) + yscaled(1/#) scaled scf; +x1 = 2.5scf; +for i=1 upto 2: + (t[i],whatever) = + fun intersectiontimes ((x[i],-infinity)--(x[i],infinity)); + z[i] = point t[i] of fun; + z[i]-(x[i+1],0) = whatever*direction t[i] of fun; + draw (x[i],0)--z[i]--(x[i+1],0); + fill fullcircle scaled 3bp shifted z[i]; +endfor +label.bot(btex $x_1$ etex, (x1,0)); +label.bot(btex $x_2$ etex, (x2,0)); +label.bot(btex $x_3$ etex, (x3,0)); +draw (0,0)--(3.2scf,0); +pickup pencircle scaled 1pt; +draw fun; +endfig; +\end{verbatim} +\atop \includegraphics{mpman-26.mps} +$$ +\caption{MetaPost code and the resulting figure} +\label{fig25} +\end{figure} + +If you know a slope and you want to find a point on a curve where the +tangent line has that slope, the {\tt directiontime}\index{directiontime +of?\texttt{directiontime of}}\label{Ddtimof} operator inverts the {\tt +direction of} operation. Given a direction vector and a path, +$$ {\tt directiontime}\, \descr{pair expression}\, {\tt of}\, + \descr{path primary} +$$ +returns a numeric value that gives the first time~$t$ when the path has +the indicated direction. (If there is no such time, the result is +$-1$). For example, if {\tt a} is the path drawn as a thin curve in +Figure~\ref{fig24}, {\tt directiontime (1,1) of a} returns 0.2084. + +There is also an predefined macro \index{directionpoint +of?\texttt{directionpoint of}}\label{Ddpntof} +$$ {\tt directionpoint}\, \descr{pair expression}\, {\tt of}\, + \descr{path primary} +$$ +that finds the first point on a path where a given direction is achieved. The +{\tt directionpoint} macro produces an error message if the direction does not +occur on the path. + +Operators {\tt +arclength}\index{arclength?\texttt{arclength}}\label{Darclng} and {\tt +arctime of}\index{arctime of?\texttt{arctime of}}\label{Darctim} relate +the ``time'' on a path to the more familiar concept of arc +length.\index{arc length}\footnote{The {\tt arclength} and {\tt arctime} +operators are only found in MetaPost version 0.50 and higher.} The +expression +$$ \hbox{{\tt arclength} \tdescr{path primary}} $$ +gives the arc length of a path. If {\tt p} is a path and {\tt a} is a number +between 0 and {\tt arclength p}, +$$ \hbox{\tt arctime a of p} $$ +gives the time~{\tt t} such that +$$ \hbox{\tt arclength subpath (0,t) of p} = {\tt a}. $$ + +The operator {\tt + envelope}\index{envelope?\texttt{envelope}}\label{Denvelop} % +returns the envelope of a path {\tt p} drawn with a polygonal pen, +and returns an error if the pen is not polygonal. +Figure~\ref{fig261} shows the envelope of an approximation of an elliptical pen. + +\begin{figure}[htp] +$$ \begin{verbatim} +beginfig(261); +path p[] ; +pen mypen ; +pen mypenC; +numeric L ; +numeric S ; +L:=10; +Sa:=1; +Sb:=2; +Rot=32; +p[-1] := ( (Sa*cosd(0),Sb*sind(0)) for i=1 upto L-1: + -- (Sa*cosd(i/L*360), Sb*sind(i/L*360)) endfor -- cycle ) rotated Rot; +mypen := makepen(p[-1]) ; +mypenC:= (pencircle xscaled 2Sa yscaled 2Sb) rotated Rot; +p0 := (0,0){down} .. {up} (100,0) ; +p1 := envelope mypen of p0 ; +draw p1 withcolor black withpen pencircle scaled 0.2pt ; +draw p0 withcolor 0.8white withpen mypenC; +for t=1 upto length(p1): + draw (point t of p1) withpen pencircle scaled 0.8pt; +endfor; +endfig; +\end{verbatim} +\atop \includegraphics[width=0.9\textwidth]{mpman-261.mps} +$$ +\caption{Example of envelope} +\label{fig261} +\end{figure} + + + +\subsection{Affine Transformations} +\label{transsec} +\index{transform type} + +Note how path {\tt fun} in Figure~\ref{fig25} is first constructed as +$$ \hbox{\verb|(0,-.1)..(1,.05){right}..(1.9,.02){right}..{curl .1}(3.2,.2)|} $$ +and then the {\tt yscaled}\index{yscaled?\texttt{yscaled}} and {\tt +scaled}\index{scaled?\texttt{scaled}} operators are used to adjust the +shape and size of the path. As the name suggests, an expression +involving ``{\tt yscaled 10}'' multiplies $y$ coordinates by ten so that +every point $(x,y)$ on the original path corresponds to a point +$(x,10y)$ on the transformed path. + +Including {\tt scaled} and {\tt yscaled}, there are seven transformation +operators that take a numeric or pair +argument:\index{shifted?\texttt{shifted}}% +\index{rotated?\texttt{rotated}}\index{slanted?\texttt{slanted}}\index{scaled?\texttt{scaled}}\index{xscaled?\texttt{xscaled}}% +\index{yscaled?\texttt{yscaled}}\index{zscaled?\texttt{zscaled}}\label{Dtranop} +\begin{eqnarray*} + (x,y){\tt\ shifted\ }(a,b) &=& (x+a,\, y+b); \\ + (x,y){\tt\ rotated\ }\theta &=& (x\cos\theta-y\sin\theta,\, + x\sin\theta+y\cos\theta); \\ + (x,y){\tt\ slanted\ }a &=& (x+ay,\, y); \\ + (x,y){\tt\ scaled\ }a &=& (ax,\, ay); \\ + (x,y){\tt\ xscaled\ }a &=& (ax,\, y); \\ + (x,y){\tt\ yscaled\ }a &=& (x,\, ay); \\ + (x,y){\tt\ zscaled\ }(a,b) &=& (ax-by,\, bx+ay). +\end{eqnarray*} +Most of these operations are self-explanatory except for {\tt zscaled} +which can be thought of as multiplication of complex numbers. The +effect of {\tt zscaled} $(a,b)$ is to rotate and scale so as to map +$(1,0)$ into $(a,b)$. The effect of {\tt rotated}~$\theta$ is rotate +$\theta$ degrees counter-clockwise. + +Any combination of shifting, rotating, slanting, etc.\ is an affine +transformation, the net effect of which is to transform any pair $(x,y)$ +into +$$ (t_x+t_{xx}x+t_{xy}y,\, t_y+t_{yx}x+t_{yy}y), $$ +for some sextuple $(t_x,t_y,t_{xx},t_{xy},t_{yx},t_{yy})$. This +information can be stored in a variable of type transform so that {\tt +transformed T}\index{transformed?\texttt{transformed}}\label{Dtrfrmd} +might be equivalent to +$$ \hbox{\tt xscaled -1 rotated 90 shifted (1,1)} $$ +if {\tt T} is an appropriate transform variable. The +transform~{\tt T} could then be initialized with an +expression of type transform as follows: +$$ \begin{verbatim} +transform T; +T = identity xscaled -1 rotated 90 shifted (1,1); +\end{verbatim} +$$ +As this example indicates, transform expressions can be built up by +applying transformation operators to other transforms. The predefined +transformation {\tt +identity}\index{identity?\texttt{identity}}\label{Dident} is a useful +starting point for this process. This can be illustrated by +paraphrasing the above equation for {\tt T} into English: ``{\tt T} +should be the transform obtained by doing whatever {\tt identity} +does. Then scaling $x$~coordinates by $-1$, rotating $90^\circ$, and +shifting by $(1,1)$.'' This works because {\tt identity} is the +identity transformation which does nothing; i.e., {\tt transformed +identity} is a no-op. + +The syntax for transform expressions and transformation operators is given in +Figure~\ref{sytrans}. It includes two more options for +\tdescr{transformer}:\index{reflectedabout?\texttt{reflectedabout}} +$$ \hbox{\tt reflectedabout(}p, q\hbox{\tt )} $$ +reflects about the line defined by points $p$ and $q$; +and\index{rotatedaround?\texttt{rotatedaround}} +$$ \hbox{\tt rotatedaround(}p,\theta\hbox{\tt )} $$ +rotates $\theta$ degrees counter-clockwise around point $p$. For example, +the equation for initializing transform~{\tt T} could have been +$$ \hbox{\tt T = identity reflectedabout((2,0), (0,2))}. $$ + +\begin{figure}[htp] +\begin{ctabbing} +$\tt \descr{pair secondary} \rightarrow + \descr{pair secondary} \descr{transformer}$\\ +$\tt \descr{path secondary} \rightarrow + \descr{path secondary} \descr{transformer}$\\ +$\tt \descr{picture secondary} \rightarrow + \descr{picture secondary} \descr{transformer}$\\ +$\tt \descr{pen secondary} \rightarrow + \descr{pen secondary} \descr{transformer}$\\ +$\tt \descr{transform secondary} \rightarrow + \descr{transform secondary} \descr{transformer}$\\[6pt] +$\tt \descr{transformer} \rightarrow rotated \descr{numeric primary}$\\ +$\tt \qquad \;|\; scaled \descr{numeric primary}$\\ +$\tt \qquad \;|\; shifted \descr{pair primary}$\\ +$\tt \qquad \;|\; slanted \descr{numeric primary}$\\ +$\tt \qquad \;|\; transformed \descr{transform primary}$\\ +$\tt \qquad \;|\; xscaled \descr{numeric primary}$\\ +$\tt \qquad \;|\; yscaled \descr{numeric primary}$\\ +$\tt \qquad \;|\; zscaled \descr{pair primary}$\\ +$\tt \qquad \;|\; reflectedabout\hbox{\tt (}\descr{pair expression} + \hbox{\tt ,}\descr{pair expression}\hbox{\tt )}$\\ +$\tt \qquad \;|\; rotatedaround\hbox{\tt (}\descr{pair expression} + \hbox{\tt ,}\descr{numeric expression}\hbox{\tt )}$ +\end{ctabbing} +\caption{The syntax for transforms and related operators} +\label{sytrans} +\end{figure} + +There is also a unary operator {\tt +inverse}\index{inverse?\texttt{inverse}}\label{Dinv} that takes a +transform and finds another transform that undoes the effect of the +first transform. Thus if +$$ p = q{\tt\ transformed\ }T $$ +then +$$ q = p{\tt\ transformed\ inverse\ }T. $$ + +It is not legal to take the {\tt inverse} of an +unknown transform\index{transformation!unknown} but we +have already seen that you can say +$$ \hbox{\tt T = } \descr{transform expression} $$ +when {\tt T} has not been given a value yet. It is also possible to +apply an unknown transform to a known pair or transform and use the +result in a linear equation. Three such equations are sufficient to +determine a transform. Thus the equations +$$ \begin{verbatim} +(0,1) transformed T' = (3,4); +(1,1) transformed T' = (7,1); +(1,0) transformed T' = (4,-3); +\end{verbatim} +$$ +allow MetaPost to determine that the transform {\tt T'} is a combination of +rotation and scaling with +$$\openup\jot + \tabskip=0pt plus 1fil + \halign to\displaywidth{\tabskip=0pt + \hfil$\displaystyle{#}$& $\displaystyle{{}#}$\hfil \qquad& + \hfil$\displaystyle{#}$& $\displaystyle{{}#}$\hfil + \tabskip=0pt plus 1fil\cr +\noalign{\vskip-\jot} + t_{xx}&=4,& t_{yx}&=-3,\cr + t_{yx}&=3,& t_{yy}&=4,\cr + t_x&=0,& t_y&=0.\cr} +$$ + +Equations involving an unknown transform are treated as linear equations +in the six parameters that define the transform. These six parameters +can also be referred to directly +as\index{xpart?\texttt{xpart}}\index{ypart?\texttt{ypart}}\index{xxpart?\texttt{xxpart}}% +\index{xypart?\texttt{xypart}}\index{yxpart?\texttt{yxpart}}\index{yypart?\texttt{yypart}}\label{Dtrprt} +$$ {\tt xpart\ T},\ {\tt ypart\ T},\ {\tt xxpart\ T},\ {\tt xypart\ T},\ + {\tt yxpart\ T},\ {\tt yypart\ T}, +$$ +where {\tt T} is a transform. For instance, Figure~\ref{fig27} uses the +equations +$$ \hbox{\tt xxpart T=yypart T; yxpart T=-xypart T} $$ +to specify that {\tt T} is shape preserving; i.e., it is a combination of +rotating, shifting, and uniform scaling. + +\begin{figure}[htp] +$$\begin{verbatim} +beginfig(28); +path p[]; +p1 = fullcircle scaled .6in; +z1=(.75in,0)=-z3; +z2=directionpoint left of p1=-z4; +p2 = z1..z2..{curl1}z3..z4..{curl 1}cycle; +fill p2 withcolor .4[white,black]; +unfill p1; +draw p1; +transform T; +z1 transformed T = z2; +z3 transformed T = z4; +xxpart T=yypart T; yxpart T=-xypart T; +picture pic; +pic = currentpicture; +for i=1 upto 2: + pic:=pic transformed T; + draw pic; +endfor +dotlabels.top(1,2,3); dotlabels.bot(4); +endfig; +\end{verbatim} +\quad \mathcenter{\includegraphics{mpman-28.mps}} +$$ +\caption{MetaPost code and the resulting ``fractal'' figure} +\label{fig27} +\end{figure} + + +\subsection{Dashed Lines} + +The MetaPost language provides many ways of changing the appearance of a +line besides just changing its width. One way is to use dashed lines as +was done in Figures \ref{fig4} and~\ref{fig22}. The syntax for this +is\index{dashed?\texttt{dashed}}\label{Ddashed} +$$ {\tt draw}\, \descr{path expression}\, {\tt dashed}\, \descr{dash pattern} $$ +where a \tdescr{dash pattern}\index{dash pattern?\tdescr{dash pattern}} +is really a special type of \tdescr{picture expression}. There is a +predefined \tdescr{dash pattern} called {\tt +evenly}\index{evenly?\texttt{evenly}}\label{Devenly} that makes dashes 3 +PostScript points long separated by gaps of the same size. Another +predefined dash pattern {\tt +withdots}\index{withdots?\texttt{withdots}}\label{Dwdots} produces +dotted lines with dots 5 PostScript points apart.\footnote{{\tt +withdots} is only found in MetaPost version 0.50 and higher.} For dots +further apart or longer dashes further apart, the \tdescr{dash pattern} +can be scaled\index{scaled?\texttt{scaled}} as shown in +Figure~\ref{fig28}. + +\begin{figure}[htp] +$$ \includegraphics{mpman-29.mps} $$ +\caption[Dashed lines and the corresponding dash patters] + {Dashed lines each labeled with the \tdescr{dash pattern} used to create + it.} +\label{fig28} +\end{figure} + +Another way to change a dash pattern is to alter its phase by shifting +it horizontally. Shifting to the right makes the dashes move forward +along the path and shifting to the left moves them backward. +Figure~\ref{fig29} illustrates this effect. The dash pattern can be +thought of as an infinitely repeating pattern strung out along a +horizontal line where the portion of the line to the right of the +$y$~axis is laid out along the path to be dashed\index{dash +pattern?\tdescr{dash pattern}}. + +\begin{figure}[htp] +$$ \includegraphics{mpman-30.mps} $$ +\caption[Dashed lines and the corresponding dash patters] + {Dashed lines and the MetaPost statements for drawing them where {\tt e4} + refers to the dash pattern {\tt evenly scaled 4}.} +\label{fig29} +\end{figure} + +When you shift a dash pattern so that the $y$~axis crosses the middle of +a dash, the first dash gets truncated. Thus the line with dash pattern +{\tt e4} starts with a dash of length 12bp followed by a 12bp gap and +another 12bp dash, etc., while {\tt e4 shifted (-6bp,0)} produces a 6bp +dash, a 12 bp gap, then a 12bp dash, etc. This dash pattern could be +specified more directly via the {\tt dashpattern}\index{dash +pattern?\texttt{dash pattern}}\label{Ddshpat} function: +$$ \hbox{\tt dashpattern(on 6bp off 12bp on 6bp)} $$ +This means ``draw the first 6bp of the line, then skip the next 12bp, then draw +another 6bp and repeat.'' If the line to be dashed is more than 30bp long, the +last 6bp of the first copy of the dash pattern will merge with the first 6bp of +the next copy to form a dash 12bp long. The general syntax for the +{\tt dashpattern} function is shown in Figure~\ref{sydash}. + +\begin{figure}[htp] +\begin{ctabbing} +$\tt \descr{dash pattern} \rightarrow dashpattern + \hbox{\tt (}\descr{on/off list}\hbox{\tt )}$\\ +$\tt \descr{on/off list} \rightarrow + \descr{on/off list}\descr{on/off clause} \;|\; \descr{on/off clause}$\\ +$\tt \descr{on/off clause} \rightarrow on \descr{numeric tertiary} + \;|\; off \descr{numeric tertiary}$ +\end{ctabbing} +\caption{The syntax for the {\tt dashpattern} function} +\label{sydash} +\end{figure} + +Since a dash pattern is really just a special kind of picture, the {\tt +dashpattern} function returns a picture. It is not really necessary to +know the structure of such a picture, so the casual reader will probably +want to skip on to Section~\ref{oopt}. For those who want to know, a +little experimentation shows that if {\tt d} is +$$ \hbox{\tt dashpattern(on 6bp off 12bp on 6bp)}, $$ +then {\tt llcorner d} is $(0,24)$ and {\tt urcorner d} is $(24,24)$. +Drawing {\tt d} directly without using it as a dash pattern produces two +thin horizontal line segments like this: +$$ \includegraphics{mpman-31.mps} $$ +The lines in this example are specified as having width zero, but this +does not matter because the line width is ignored when a picture is used +as a dash pattern. + +The general rule for interpreting a picture {\tt d} as a dash pattern is +that the line segments in {\tt d} are projected onto the $x$-axis and +the resulting pattern is replicated to infinity in both directions by +placing copies of the pattern end-to-end. The actual dash lengths are +obtained by starting at $x=0$ and scanning in the positive $x$ +direction. + +To make the idea of ``replicating to infinity'' more precise, let $P({\tt d})$ +be the projection of {\tt d} onto the $x$~axis, and let +${\rm shift}(P({\tt d}),x)$ be the result of shifting {\tt d} by~$x$. +The pattern resulting from infinite replication is +$$ \bigcup_{{\rm integers}\ n} {\rm shift}(P(d),\, n\cdot\ell(d)), $$ +where $\ell(d)$ measures the length of $P(d)$. The most restrictive possible +definition of this length is $d_{\rm max}-d_{\rm min}$, +where $[d_{\rm min},d_{\rm max}]$ +is the range of $x$~coordinates in $P(d)$. In fact, MetaPost uses +$$ \max(\left|y_0({\tt d})\right|,\, d_{\rm max}-d_{\rm min}), $$ +where $y_0({\tt d})$ is the $y$ coordinate of the contents of {\tt d}. +The contents of {\tt d} should lie on a horizontal line, but if they do +not, the MetaPost interpreter just picks a $y$~coordinate that occurs in +{\tt d}\index{dash pattern?\tdescr{dash pattern}}. + +A picture used as a dashed pattern must contain no text or filled +regions, but it can contain lines that are themselves dashed. This can +give small dashes inside of larger dashes as shown in +Figure~\ref{fig32}.\index{dash pattern?\tdescr{dash pattern}!recursive} + +\begin{figure}[htp] +$$\begin{verbatim} +beginfig(32); +draw dashpattern(on 15bp off 15bp) dashed evenly; +picture p; +p=currentpicture; +currentpicture:=nullpicture; +draw fullcircle scaled 1cm xscaled 3 dashed p; +endfig; +\end{verbatim} +\quad \mathcenter{\includegraphics{mpman-32.mps}} +$$ +\caption{MetaPost code for dashed patterns and the corresponding output} +\label{fig32} +\end{figure} + +\label{dashed-pens} +Also, dashed patterns are intended to be used either with {\tt +pencircle} or no pen at all; {\tt pensquare} and other complex pens +should be avoided. This is because the output uses the PostScript +primitive {\tt setdash}, which does not interact well with the filled +paths created by polygonal pens. See Section~\ref{sec.pens}, p.\ +\pageref{sec.pens}. + +%\newpage + +\subsection{Local specials} + +If you want to attach a special bit of PostScript code, you can use +$$ +{\tt withprescript} \descr{string expression}% +\index{withprescript?\texttt{withprescript}}\label{Dwithpre} +$$ +and +$$ +{\tt withpostscript} \descr{string expression}% +\index{withpostscript?\texttt{withpostscript}}\label{Dwithpost} +$$ +The strings will be written to the output file before and after the +current object, each beginning on their own line. You can specify +multiple {\tt withprescript} or {\tt withpostscript} options if you +like. + +When you specify more than one {\tt withprescript} or more than one {\tt + withpostscript} option, be wary of the fact that the scripts use a +form of nesting: the {\tt withprescript} items are written to the +PostScript file in last in, first out order; whereas the {\tt + withpostscript} items are written in first in, first out order. + +\subsection{Other Options} +\label{oopt} + +You might have noticed that the dashed lines produced by {\tt dashed +evenly}\index{evenly?\texttt{evenly}} appear to have more black than +white. This is an effect of the {\tt +linecap}\index{linecap?\texttt{linecap}}\label{Dlinecap} parameter that +controls the appearance of the ends of lines as well as the ends of +dashes. There are also a number of other ways to affect the appearance +of things drawn with MetaPost. + +The {\tt linecap} parameter has three different settings just as in +PostScript. Plain MetaPost gives this internal variable\index{internal +variables}\index{variables!internal} the default value {\tt +rounded}\index{rounded?\texttt{rounded}} which causes line segments to +be drawn with rounded ends like the segment from {\tt z0} to {\tt z3} in +Figure~\ref{fig33}. Setting ${\tt linecap}\mathrel{\hbox{\tt:=}}{\tt +butt}$\index{butt?\texttt{butt}}\label{Dbutt} cuts the ends off flush so +that dashes produced by {\tt dashed +evenly}\index{evenly?\texttt{evenly}} have length 3bp, not 3bp plus the +line width. You can also get squared-off ends that extend past the +specified endpoints by setting ${\tt linecap}\mathrel{\hbox{\tt:=}}{\tt +squared}$\index{squared?\texttt{squared}}\label{Dsqred} as was done in +the line from {\tt z2} to {\tt z5} in Figure~\ref{fig33}. + +\begin{figure}[htp] +$$\begin{verbatim} +beginfig(33); +for i=0 upto 2: + z[i]=(0,40i); z[i+3]-z[i]=(100,30); +endfor +pickup pencircle scaled 18; +draw z0..z3 withcolor .8white; +linecap:=butt; +draw z1..z4 withcolor .8white; +linecap:=squared; +draw z2..z5 withcolor .8white; +dotlabels.top(0,1,2,3,4,5); +endfig; linecap:=rounded; +\end{verbatim} +\qquad +\mathcenter{\includegraphics{mpman-33.mps}} +$$ +\caption{MetaPost code and the corresponding output} +\label{fig33} +\end{figure} + +Another parameter borrowed from PostScript affects the way a {\tt draw} +statement treats sharp corners\index{corners} in the path to be drawn. +The {\tt linejoin}\index{linejoin?\texttt{linejoin}}\label{Dlinejoin} +parameter can be {\tt +rounded}\index{rounded?\texttt{rounded}}\label{Drnded}, {\tt +beveled}\index{beveled?\texttt{beveled}}\label{Dbvled}, or {\tt +mitered}\index{mitered?\texttt{mitered}}\label{Dmitred} as shown in +Figure~\ref{fig34}. The default value for plain MetaPost is {\tt +rounded} which gives the effect of drawing with a circular brush. + +\begin{figure}[htp] +$$\begin{verbatim} +beginfig(34); +for i=0 upto 2: + z[i]=(0,50i); z[i+3]-z[i]=(60,40); + z[i+6]-z[i]=(120,0); +endfor +pickup pencircle scaled 24; +draw z0--z3--z6 withcolor .8white; +linejoin:=mitered; +draw z1..z4--z7 withcolor .8white; +linejoin:=beveled; +draw z2..z5--z8 withcolor .8white; +dotlabels.bot(0,1,2,3,4,5,6,7,8); +endfig; linejoin:=rounded; +\end{verbatim} +\qquad +\mathcenter{\includegraphics{mpman-34.mps}} +$$ +\caption{MetaPost code and the corresponding output} +\label{fig34} +\end{figure} + +When {\tt linejoin} is {\tt mitered}, sharp corners generate long +pointed features as shown in Figure~\ref{fig35}. Since this might be +undesirable, there is an internal variable\index{internal +variables}\index{variables!internal} called {\tt +miterlimit}\index{miterlimit?\texttt{miterlimit}}\label{Dmiterlim} that +controls how extreme the situation can get before the mitered join is +replaced by a beveled join. For Plain MetaPost, {\tt miterlimit} has a +default value of 10.0 and line joins revert to beveled when the ratio of +miter length to line width reaches this value. + +\begin{figure}[htp] +$$ \includegraphics{mpman-35.mps} $$ +\caption{The miter length and line width whose ratio is limited by + {\tt miterlimit}.} +\label{fig35} +\end{figure} + +The {\tt linecap}, {\tt linejoin}, and {\tt miterlimit} parameters are +especially important because they also affect things that get drawn +behind the scenes. For instance, Plain MetaPost has statements for +drawing arrows\index{arrows}, and the arrowheads are slightly rounded +when {\tt linejoin} is {\tt rounded}. The effect depends on the line +width and is quite subtle at the default line width of 0.5bp as shown in +Figure~\ref{fig36}. + +\begin{figure}[htp] +$$\includegraphics{mpman-36.mps}$$ +\caption{Three ways of drawing arrows.} +\label{fig36} +\end{figure} + +Drawing arrows like the ones in Figure~\ref{fig36} is simply a matter of +saying\index{drawarrow?\texttt{drawarrow}}\label{Ddrwarr} +$$ {\tt drawarrow}\, \descr{path expression} $$ +instead of {\tt draw} \tdescr{path expression}. This draws the given +path with an arrowhead at the last point on the path. If you want the +arrowhead at the beginning of the path, just use the unary operator {\tt +reverse}\index{reverse?\texttt{reverse}}\label{Drevrse} to take the +original path and make a new one with its time sense reversed; i.e., for +a path~{\tt p} with {\tt length p}${}=n$, +$$ {\tt point\ } t {\tt\ of\ reverse\ p} + \quad {\rm and} \quad + {\tt point\ } n-t {\tt\ of\ p} +$$ are synonymous. + +As shown in Figure~\ref{fig36}, a statement +beginning\index{drawdblarrow?\texttt{drawdblarrow}}% +\index{arrows!double-headed}\label{Ddrwdar} +$$ {\tt drawdblarrow}\, \descr{path expression} $$ +draws a double-headed arrow. The size of the arrowhead is guaranteed to +be larger than the line width, but it might need adjusting if the line +width is very great. This is done by assigning a new value to the +internal variable\index{internal variables}\index{variables!internal} +{\tt ahlength}\index{ahlength?\texttt{ahlength}}\label{Dahlength} that +determines arrowhead length as shown in Figure~\ref{fig37}. Increasing +{\tt ahlength} from the default value of 4 PostScript points to 1.5 +centimeters produces the large arrowhead in Figure~\ref{fig37}. There +is also an {\tt ahangle}\index{ahangle?\texttt{ahangle}}\label{Dahangle} +parameter that controls the angle at the tip of the arrowhead. The +default value of this angle is 45 degrees as shown in the figure. + +\begin{figure}[htp] +$$ \includegraphics{mpman-37.mps} $$ +\caption[A large arrowhead with key parameters labeled.] + {A large arrowhead with key parameters labeled and paths used to + draw it marked with white lines.} +\label{fig37} +\end{figure} + +The arrowhead is created by filling the triangular region that is +outlined in white in Figure~\ref{fig37} and then drawing around it with +the currently picked up pen. This combination of filling and drawing +can be combined into a single {\tt filldraw} +statement\index{filldraw?\texttt{filldraw}}\label{Dfildrw}: +$$ {\tt filldraw}\, \descr{path expression}\, + \descr{optional {\tt dashed} and {\tt withcolor} and {\tt withpen} clauses}; +$$ +The \tdescr{path expression} should be a closed cycle like the +triangular path in Figure~\ref{fig37}. This path should not be confused +with the path argument to {\tt drawarrow} which is indicated by a white +line in the figure. + +White lines like the ones in the figure can be created by an {\tt +undraw}\index{undraw?\texttt{undraw}}\label{Dundraw} statement. This is +an erasing\index{erasing} version of {\tt draw} that draws {\tt +withcolor background}\index{background?\texttt{background}} just as the +{\tt unfill} statement does. There is also an {\tt +unfilldraw}\index{unfilldraw?\texttt{unfilldraw}}\label{Dunfdrw} +statement just in case someone finds a use for it. + +The {\tt filldraw}, {\tt undraw} and {\tt unfilldraw} statements and all +the arrow drawing statements are like the {\tt fill} and {\tt draw} +statements in that they take {\tt dashed}\index{dashed?\texttt{dashed}}, +{\tt withpen}\index{withpen?\texttt{withpen}}, and {\tt +withcolor}\index{withcolor?\texttt{withcolor}} options. When you have a +lot of drawing statements it is nice to be able to apply an option such +as {\tt withcolor 0.8white} to all of them without having to type this +repeatedly as was done in Figures \ref{fig33} and~\ref{fig34}. The +statement for this purpose +is\index{drawoptions?\texttt{drawoptions}}\label{Ddropts} +$$ \hbox{\tt drawoptions(} \descr{text} \hbox{\tt )} $$ +where the \tdescr{text} argument gives a sequence of {\tt dashed}, {\tt +withcolor}, and {\tt withpen} options to be applied automatically to all +drawing statements. If you specify +$$ \hbox{\tt drawoptions(withcolor .5[black,white])} $$ +and then want to draw a black line, you can override the {\tt drawoptions} +by specifying +$$ {\tt draw}\, \descr{path expression}\, {\tt withcolor\ black} $$ +To turn off {\tt drawoptions} all together, just give an empty list: +$$ \hbox{\tt drawoptions()} $$ +(This is done automatically by the {\tt +beginfig}\index{beginfig?\texttt{beginfig}} macro). + +Since irrelevant options are ignored, there is no harm in giving a statement +like +$$ \hbox{\tt drawoptions(dashed evenly)} $$ +followed by a sequence of {\tt draw} and {\tt fill} commands. It does +not make sense to use a dash pattern when filling so the {\tt dashed +evenly} gets ignored for {\tt fill} statements. It turns out that +$$ \hbox{\tt drawoptions(withpen } \descr{pen expression} \hbox{\tt )} $$ +does affect {\tt fill} statements as well as {\tt draw} statements. +In fact there is a special pen variable called +{\tt currentpen}\index{currentpen?\texttt{currentpen}} such that +{\tt fill} \ldots\ {\tt withpen currentpen} is equivalent to a {\tt filldraw} +statement. + +Precisely what does it mean to say that drawing options affect those +statements where they make sense? The {\tt dashed} \tdescr{dash +pattern} option only affects +$$ {\tt draw}\, \descr{path expression} $$ +statements, and text appearing in the \tdescr{picture expression} argument to +$$ {\tt draw}\, \descr{picture expression} $$ +statement is only affected by the {\tt withcolor} \tdescr{color +expression} option. For all other combinations of drawing statements +and options, there is some effect. An option applied to a {\tt draw} +\tdescr{picture expression} statement will in general affect some parts +of the picture but not others. For instance, a {\tt dashed} or {\tt +withpen} option will affect all the lines in the picture but none of the +labels. + + +\subsection{Pens} +\label{sec.pens} + +Previous sections have given numerous examples of {\tt pickup} +\tdescr{pen expression} and {\tt withpen} \tdescr{pen expression}, but +there have not been any examples of pen expressions other than +$$ {\tt pencircle\ scaled}\, \descr{numeric primary} $$ +which produces lines of a specified width. For calligraphic effects +such in Figure~\ref{fig38}, you can apply any of the transformation +operators discussed in Section~\ref{transsec}. The starting point for +such transformations is {\tt +pencircle}\index{pencircle?\texttt{pencircle}}\label{Dpncirc}, a circle +one PostScript point in diameter. Thus affine transformations produce a +circular or elliptical\index{pens!elliptical} pen shape. The width of +lines drawn with the pen depends on how nearly perpendicular the line is +to the long axis of the ellipse. + +\begin{figure}[htp] +$$\begin{verbatim} +beginfig(38); +pickup pencircle scaled .2in yscaled .08 rotated 30; +x0=x3=x4; +z1-z0 = .45in*dir 30; +z2-z3 = whatever*(z1-z0); +z6-z5 = whatever*(z1-z0); +z1-z6 = 1.2*(z3-z0); +rt x3 = lft x2; +x5 = .55[x4,x6]; +y4 = y6; +lft x3 = bot y5 = 0; +top y2 = .9in; +draw z0--z1--z2--z3--z4--z5--z6 withcolor .7white; +dotlabels.top(0,1,2,3,4,5,6); +endfig; +\end{verbatim} +\quad \mathcenter{\includegraphics{mpman-38.mps}} +$$ +\caption{MetaPost code and the resulting ``calligraphic'' figure.} +\label{fig38}\index{lft?\texttt{lft}}\index{bot?\texttt{bot}}\index{top?\texttt{top}} +\end{figure} + +Figure~\ref{fig38} demonstrates operators {\tt +lft}\index{lft?\texttt{lft}}\label{Dlft}, {\tt +rt}\index{rt?\texttt{rt}}\label{Drt}, {\tt +top}\index{top?\texttt{top}}\label{Dtop}, and {\tt +bot}\index{bot?\texttt{bot}}\label{Dbot} that answer the question, ``If +the current pen is placed at the position given by the argument, where +will its left, right, top, or bottom edge be?'' In this case the +current pen is the ellipse given in the {\tt pickup} statement and its +bounding box is 0.1734 inches wide and 0.1010 inches high, so {\tt rt +x3} is ${\tt x3}+{\tt 0.0867in}$ and {\tt bot y5} is ${\tt y5}-{\tt +0.0505in}$. The {\tt lft}, {\tt rt}, {\tt top}, and {\tt bot} operators +also accept arguments of type pair in which case they compute the $x$ +and~$y$ coordinates of the leftmost, rightmost, topmost, or bottommost +point on the pen shape. For example, +$$ {\tt rt}(x,y) = (x,y)+({\tt 0.0867in}, {\tt 0.0496in}) $$ +for the pen in Figure~\ref{fig38}. Note that {\tt +beginfig}\index{beginfig?\texttt{beginfig}} resets the current pen to a +default value of +$$ \hbox{\tt pencircle scaled 0.5bp} $$ +at the beginning of each figure. This value can be reselected at any +time by giving the command {\tt pickup +defaultpen}\index{defaultpen?\texttt{defaultpen}}\label{Ddefaultpen}. + +This would be the end of the story on pens, except that for +compatibility with \MF\index{metafont?\MF}, MetaPost also allows pen +shapes to be polygonal\index{pens!polygonal}. There is a predefined pen +called {\tt pensquare}\index{pensquare?\texttt{pensquare}}\label{Dpnsqr} +that can be transformed to yield pens shaped like parallelograms. + +In fact, there is even an operator called {\tt +makepen}\index{makepen?\texttt{makepen}}\label{Dmkpen} that takes a +convex-polygon-shaped path and makes a pen that shape and size. If the +path is not exactly convex or polygonal, the {\tt makepen} operator will +straighten the edges and/or drop some of the vertices. In particular, +{\tt pensquare} is equivalent to +$$ \hbox{\verb|makepen((-.5,-.5)--(.5,-.5)--(.5,.5)--(-.5,.5)--cycle)|} $$ + +{\tt pensquare} and {\tt makepen} should not be used with dash +patterns. See the end of Section~\ref{dashed-pens}, p.\ +\pageref{dashed-pens}. + +The inverse of {\tt makepen} is the {\tt +makepath}\index{makepath?\texttt{makepath}}\label{Dmkpath} operator that +takes a \tdescr{pen primary} and returns the corresponding path. Thus +{\tt makepath pencircle} produces a circular path identical to {\tt +fullcircle}\index{fullcircle?\texttt{fullcircle}}. This also works for +a polygonal pen so that +$$ {\tt makepath\ makepen}\, \descr{path expression} $$ +will take any cyclic path and turn it into a convex polygon\index{convex polygons}. + + +\subsection{Clipping and Low-Level Drawing Commands} + +Drawing statements such as {\tt draw}, {\tt fill}, {\tt filldraw}, and +{\tt unfill} are part of the Plain macro\index{Plain macros} package and +are defined in terms of more primitive statements. The main difference +between the drawing statements discussed in previous sections and the +more primitive versions is that the primitive drawing statements all +require you to specify a picture variable to hold the results. For {\tt +fill}, {\tt draw}, and related statements, the results always go to a +picture variable called {\tt +currentpicture}\index{currentpicture?\texttt{currentpicture}}\label{Dcurpic}. +The syntax for the primitive drawing statements that allow you to +specify a picture variable is shown in Figure~\ref{sydraw}. + +\begin{figure}[htp] +\begin{ctabbing} +$\tt \descr{addto command} \rightarrow$\\ +$\tt \qquad addto \descr{picture variable} also + \descr{picture expression} \descr{option list}$\\ +$\tt \qquad \;|\; addto \descr{picture variable} + contour \descr{path expression} \descr{option list}$\\ +$\tt \qquad \;|\; addto \descr{picture variable} + doublepath \descr{path expression} \descr{option list}$\\ +$\tt \descr{option list} \rightarrow \descr{empty} \;|\; + \descr{drawing option} \descr{option list}$\\ +$\tt \descr{drawing option} \rightarrow withcolor \descr{color expression}$\\ +$\tt \qquad \;|\; withrgbcolor \descr{rgbcolor expression} \;|\; + withcmykcolor \descr{cmykcolor expression}$\\ +$\tt \qquad \;|\; withgreyscale \descr{numeric expression} \;|\; + withoutcolor$\\ +$\tt \qquad \;|\; withprescript \descr{string expression} \;|\; + withpostscript \descr{string expression}$\\ +$\tt \qquad \;|\; withpen \descr{pen expression} \;|\; + dashed \descr{picture expression}$ +\end{ctabbing} +\caption{The syntax for primitive drawing statements} +\label{sydraw} +\index{option list?\tdescr{option list}}\index{addto also?\texttt{addto also}}\index{addto contour?\texttt{addto contour}}% +\index{addto doublepath?\texttt{addto doublepath}}\index{withcolor?\texttt{withcolor}}\index{withpen?\texttt{withpen}}% +\index{dashed?\texttt{dashed}}\index{drawing option?\tdescr{drawing option}} +\end{figure} + +The syntax for primitive drawing commands is compatible with +\MF\index{metafont?\MF}. Table~\ref{draweqv} shows how the primitive +drawing statements relate to the familiar {\tt draw} and {\tt fill} +statements. Each of the statements in the first column of the table +could be ended with an \tdescr{option list} of its own, which is +equivalent to appending the \tdescr{option list} to the corresponding +entry in the second column of the table. For example, +$$ {\tt draw}\ p\ {\tt withpen\ pencircle} $$ +is equivalent to +$$ {\tt addto\ currentpicture\ doublepath}\ p\ + {\tt withpen\ currentpen\ withpen\ pencircle} +$$ +where {\tt +currentpen}\index{currentpen?\texttt{currentpen}}\label{Dcurpen} is a +special pen variable that always holds the last pen picked up. The +second {\tt withpen} option silently overrides the {\tt withpen +currentpen} from the expansion of {\tt draw}. + +\begin{table}[htp] +$$\begin{tabular}{|l|l|} \hline +\multicolumn1{|c|}{statement}& \multicolumn1{c|}{equivalent primitives}\\ \hline +{\tt draw} {\it pic}& {\tt addto currentpicture also} {\it pic}\\ +{\tt draw} $p$& {\tt addto currentpicture doublepath} $p$ + {\tt withpen} $q$\\ +{\tt fill} $c$& {\tt addto currentpicture contour} $c$\\ +{\tt filldraw} $c$& {\tt addto currentpicture contour} $c$ {\tt withpen} $q$\\ +{\tt undraw} {\it pic}& {\tt addto currentpicture also} {\it pic} + {\tt withcolor} $b$\\ +{\tt undraw} $p$& {\tt addto currentpicture doublepath} $p$ + {\tt withpen} $q$ + {\tt withcolor} $b$\\ +{\tt unfill} $c$& {\tt addto currentpicture contour} $c$ + {\tt withcolor} $b$\\ +{\tt unfilldraw} $c$& {\tt addto currentpicture contour} $c$ {\tt withpen} $q$ + {\tt withcolor} $b$\\ \hline +\end{tabular} +$$ +\caption[Drawing statements and equivalent primitive commands] {Common + drawing statements and equivalent primitive versions, where $q$ + stands for {\tt currentpen}, $b$ stands for {\tt background}, + $p$ stands for any path, $c$ stands for a cyclic path, and {\it + pic} stands for a \tdescr{picture expression}. Note that + nonempty {\tt drawoptions} would complicate the entries in the + second column.} +\label{draweqv} +\index{drawoptions?\texttt{drawoptions}} +\end{table} + + +There are two more primitive drawing commands that do not accept any +drawing options. One is the {\tt setbounds} command that was discussed +in Section~\ref{meas}; the other is the {\tt clip} +command\index{clip?\texttt{clip}}\label{Dclip}: +$$ {\tt clip}\, \descr{picture variable}\, {\tt to}\, \descr{path expression} $$ +Given a cyclic path, this statement trims the contents of the +\tdescr{picture variable} to eliminate everything outside of the cyclic path. +There is no ``high level'' version of this statement, so you have to use +$$ {\tt clip\ currentpicture\ to}\, \descr{path expression} $$ +if you want to clip {\tt +currentpicture}\index{currentpicture?\texttt{currentpicture}}. +Figure~\ref{fig40} illustrates clipping. + +\begin{figure}[htp] +$$\begin{verbatim} +beginfig(40); +path p[]; +p1 = (0,0){curl 0}..(5pt,-3pt)..{curl 0}(10pt,0); +p2 = p1..(p1 yscaled-1 shifted(10pt,0)); +p0 = p2; +for i=1 upto 3: p0:=p0.. p2 shifted (i*20pt,0); + endfor +for j=0 upto 8: draw p0 shifted (0,j*10pt); + endfor +p3 = fullcircle shifted (.5,.5) scaled 72pt; +clip currentpicture to p3; +draw p3; +endfig; +\end{verbatim} +\qquad +\mathcenter{\includegraphics{mpman-40.mps}} +$$ +\caption{MetaPost code and the resulting ``clipped'' figure.} +\label{fig40} +\end{figure} + +All the primitive drawing operations would be useless without one last +operation called {\tt shipout}. The +statement\index{shipout?\texttt{shipout}}\label{Dship} +$$ {\tt shipout}\, \descr{picture expression} $$ +writes out a picture as a PostScript\index{PostScript} file whose +file name is determined by +{\tt outputtemplate}\index{outputtemplate?\texttt{outputtemplate}} +(see Section~\ref{Doutputtemplate}). By default, the file name ends +{\tt.}{\it nnn}, where {\tt nnn} is the decimal representation +of the value of the internal variable\index{internal +variables}\index{variables!internal} {\tt +charcode}\index{charcode?\texttt{charcode}}\label{Dcharcode}. (The name +``{\tt charcode}'' is for compatibility with \MF\index{metafont?\MF}.) +Normally, {\tt beginfig}\index{beginfig?\texttt{beginfig}} sets {\tt +charcode}, and {\tt endfig}\index{endfig?\texttt{endfig}} invokes {\tt +shipout}. + +\subsection{Directing Output to a Picture Variable} +Sometimes, it might be desirable to save the output of a drawing +operation and re-use them later. This can easily be done with +MetaPost primitives like \ttt{addto}. On the other hand, since the +higher-level drawing commands defined in the Plain macro package +always write to the +\ttt{currentpicture}\index{currentpicture?\texttt{currentpicture}}, +saving their output required to temporarily save \ttt{currentpicture}, +reset it to \ttt{nullpicture}\index{nullpicture?\texttt{nullpicture}}, +execute the drawing operations, save the \ttt{currentpicture} to a +new \ttt{picture} variable and finally restore \ttt{currentpicture} to +the saved state. In MetaPost version~0.60 a new macro +$$ \hbox{\tt image( $\descr{drawing commands}$ )} $$% +\index{image?\texttt{image}}\label{Dimage}% +was introduced that eases this task. It takes as input a sequence of arbitrary +drawing operations and returns a \ttt{picture} variable containing the +corresponding output, without affecting {\tt currentpicture}. + +As an example, in the code of figure~\ref{fig55} an object \ttt{wheel} has +been defined that saves the output of two \ttt{draw} operations as follows: +\begin{figure}[b] +$$ \includegraphics{mpman-55.mps} $$ +\caption{Copying objects with the \ttt{image} operator.} +\label{fig55} +\end{figure} +$$\begin{verbatim} +picture wheel; +wheel := image( + draw fullcircle scaled 2u xscaled .8 rotated 30; + draw fullcircle scaled .15u xscaled .8 rotated 30; +); +\end{verbatim} +$$ +This \ttt{wheel} object is re-used in the definition of another object \ttt{car}. +Figure~\ref{fig55} shows three \ttt{car} objects drawn with two different slant +values. + + +\subsection{Inspecting the Components of a Picture} +\label{piccomp} + +\mbox{}% Start paragraph here. +\index{setbounds?\texttt{setbounds}|(}% +\index{for within?\texttt{for within}|(}% +% +MetaPost pictures are composed of stroked lines, filled outlines, pieces +of typeset text, clipping paths\index{clip?\texttt{clip}}, and +{\tt setbounds}\index{setbounds?\texttt{setbounds}} paths. (A {\tt setbounds} +path gives an artificial bounding box as is needed for \TeX\ output.) +A picture can have many components of each type. They can be accessed via +an iteration of the form +$$ {\tt for}\ \descr{symbolic token}\ {\tt within}\ + \descr{picture expression}\hbox{\tt:}\ \descr{loop text}\ {\tt endfor} +$$\index{for within?\texttt{for within}}\label{Dforwithin}% +The \tdescr{loop text} can be anything that is balanced with respect to +{\tt for} and {\tt endfor}. The \tdescr{symbolic token} is a loop variable that +scans the components of the picture in the order in which they were drawn. The +component for a clipping or {\tt setbounds} path includes everything the path +applies to. Thus if a single clipping or {\tt setbounds} path applies to +everything in the \tdescr{picture expression}, the whole picture could be +thought of as one big component. In order to make the contents of such a picture +accessible, the {\tt for}\ldots{\tt within} iteration ignores the enclosing +clipping or {\tt setbounds} path in this case. The number of components +that a {\tt for}\ldots {\tt within} iteration would find is returned by +$$ {\tt length}\ \descr{picture primary}\index{length?\texttt{length}}\label{DlengthPicture}$$ + +\index{for within?\texttt{for within}|)} + +\mbox{}% Start paragraph here. +\index{stroked?\texttt{stroked}|(}% +\index{filled?\texttt{filled}|(}% +\index{textual?\texttt{textual}|(}% +\index{clipped?\texttt{clipped}|(}% +\index{bounded?\texttt{bounded}|(}% +% +Once the {\tt for}\ldots{\tt within} iteration has found a picture component, +there are numerous operators for identifying it and extracting relevant +information. The operator +$$ {\tt stroked}\ \descr{primary expression} $$\index{stroked?\texttt{stroked}}\label{Dstroked}% +tests whether the expression is a known picture whose first component is a +stroked line. Similarly, the {\tt filled}\index{filled?\texttt{filled}}\label{Dfilled} +and {\tt textual}\index{textual?\texttt{textual}}\label{Dtextual} operators +return {\tt true} if the first component is a filled outline or a piece of +typeset text. The {\tt clipped}\index{clipped?\texttt{clipped}}\label{Dclipped} +and {\tt bounded}\index{bounded?\texttt{bounded}}\label{Dbounded} operators +test whether the argument is a known picture that starts with a clipping +path or a {\tt setbounds} path. This is true if the first component is +clipped or bounded or if the entire picture is enclosed in a clipping or +{\tt setbounds} path. + +\mbox{}% Start paragraph here. +\index{pathpart?\texttt{pathpart}|(}% +\index{penpart?\texttt{penpart}|(}% +\index{dashpart?\texttt{dashpart}|(}% +% +There are also numerous part extraction operators that test the first component +of a picture. If {\tt p} is a picture and {\tt stroked p} is true, +{\tt pathpart p}\index{pathpart?\texttt{pathpart}}\label{Dpathpart} is the +path describing the line that got stroked, +{\tt penpart p}\index{penpart?\texttt{penpart}}\label{Dpenpart} is the pen +that was used, {\tt dashpart p}\index{dashpart?\texttt{dashpart}}\label{Ddashpart} +is the dash pattern. If the line is not dashed, {\tt dashpart p} +returns an empty picture. + +The same part extraction operators work when {\tt filled p} is true, except +that {\tt dashpart p} is not meaningful in that case. + +For text components, {\tt textual p} is true, +{\tt textpart p}\index{textpart?\texttt{textpart}}\label{Dtextpart} +gives the text that got typeset, +{\tt fontpart p}\index{fontpart?\texttt{fontpart}}\label{Dfontpart} +gives the font that was used, and {\tt xpart~p}\index{xpart?\texttt{xpart}}\index{ypart?\texttt{ypart}}\index{xxpart?\texttt{xxpart}}% +\index{xypart?\texttt{xypart}}\index{yxpart?\texttt{yxpart}}\index{yypart?\texttt{yypart}}, +{\tt ypart~p}, {\tt xxpart~p}, {\tt xypart~p}, {\tt yxpart~p}, {\tt yypart~p} +tell how the text has been shifted, rotated, and scaled. + +\mbox{}% Start paragraph here. +\index{colorpart?\texttt{colorpart}|(}% +\index{colormodel?\texttt{colormodel}|(}% +\index{redpart?\texttt{redpart}|(}% +\index{greenpart?\texttt{greenpart}|(}% +\index{bluepart?\texttt{bluepart}|(}% +\index{cyanpart?\texttt{cyanpart}|(}% +\index{magentapart?\texttt{magentapart}|(}% +\index{yellowpart?\texttt{yellowpart}|(}% +\index{blackpart?\texttt{blackpart}|(}% +\index{greypart?\texttt{greypart}|(}% +% +Finally, for \ttt{stroked}, \ttt{filled} and \ttt{textual} components +the color can be examined by saying +$$ {\tt colorpart}\ +\descr{item}\index{colorpart?\texttt{colorpart}}\label{Dcolorpart} +$$ +This returns the color of a component in its respective color model. +The color model of a component can be identified by the +\ttt{colormodel}\index{colormodel?\texttt{colormodel}}\label{Dcolormodel} +operator (cf. Table~\ref{dfltcmod} on p.~\pageref{dfltcmod}). + +For more fine grained color operations there are operators to extract +single color components of an item. Depending on the color model the +color of a picture component \ttt{p} is +$$ \hbox{\tt (cyanpart p, magentapart p, yellowpart p, blackpart p)} $$% +\index{cyanpart?\texttt{cyanpart}}\index{magentapart?\texttt{magentapart}}\index{yellowpart?\texttt{yellowpart}}\index{blackpart?\texttt{blackpart}} +or +$$ \hbox{\tt (redpart p, greenpart p, bluepart p)} $$% +\index{redpart?\texttt{redpart}}\index{greenpart?\texttt{greenpart}}\index{bluepart?\texttt{bluepart}} +or +$$ \hbox{\tt greypart p} $$% +\index{greypart?\texttt{greypart}} +or +$$ \hbox{\tt false}. $$ + +Note, color part operators {\tt redpart}, {\tt cyanpart} etc. have to +match the color model of the picture component in question. Applying a +non-matching color part operator to a picture component triggers an +error and returns a \ttindex{black} color part in the requested color +model. That is, for the code +$$\begin{verbatim} +picture pic; +pic := image(fill unitsquare scaled 1cm withcolor (0.3, 0.6, 0.9);); +for item within pic: + show greypart item; + show cyanpart item; + show blackpart item; + show redpart item; +endfor +\end{verbatim} +$$ +the output is (omitting the error messages) +$$\begin{verbatim} +>> 0 +>> 0 +>> 1 +>> 0.3 +\end{verbatim} +$$ +since in grey scale color model black is {\tt 0} and in CMYK color model +black is {\tt (0,0,0,1)}. For the matching RGB color model the true +color component is returned. + +When {\tt clipped p} or {\tt bounded p} is true, {\tt pathpart p} gives the +clipping or {\tt setbounds} path and the other part extraction operators are +not meaningful. Such non-meaningful part extractions do not generate +errors. Instead, they return null values or black color (components): +the trivial path {\tt (0,0)} for {\tt pathpart}, +{\tt nullpen}\index{nullpen?\texttt{nullpen}}\label{Dnlpen} for {\tt penpart}, +an empty picture for {\tt dashpart}, +the null string for {\tt textpart} or {\tt fontpart}, +zero for {\tt colormodel}, +{\tt greypart}, +{\tt redpart}, {\tt greenpart}, {\tt bluepart}, +{\tt cyanpart}, {\tt magentapart}, {\tt yellowpart}, +one for {\tt blackpart}, and +black in the current default color model for {\tt colorpart}. + +To summarize the discussion of mismatching part operators: +\begin{enumerate} +\item Asking for non-meaningful parts of an item---such as the {\tt + redpart} of a clipping path, the {\tt textpart} of a stroked item, + or the {\tt pathpart} of a textual item---is silently accepted and + returns a null value or a black color (component). +\item Explicitly asking for a color part of a colored item in the wrong + color model returns a black color component. This operation triggers + an error. +\end{enumerate} + +\index{setbounds?\texttt{setbounds}|)} +\index{stroked?\texttt{stroked}|)} +\index{filled?\texttt{filled}|)} +\index{textual?\texttt{textual}|)} +\index{clipped?\texttt{clipped}|)} +\index{bounded?\texttt{bounded}|)} +\index{pathpart?\texttt{pathpart}|)} +\index{penpart?\texttt{penpart}|)} +\index{dashpart?\texttt{dashpart}|)} +\index{colormodel?\texttt{colormodel}|)} +\index{colorpart?\texttt{colorpart}|)} +\index{redpart?\texttt{redpart}|)} +\index{greenpart?\texttt{greenpart}|)} +\index{bluepart?\texttt{bluepart}|)} +\index{cyanpart?\texttt{cyanpart}|)} +\index{magentapart?\texttt{magentapart}|)} +\index{yellowpart?\texttt{yellowpart}|)} +\index{blackpart?\texttt{blackpart}|)} +\index{greypart?\texttt{greypart}|)} + + +\subsection{Decomposing the Glyphs of a Font} +\label{glyphs} + +MetaPost provides a primitive to convert a +glyph\index{glyph}\index{font!glyph} of a font in the Adobe Type~1 +Font\index{PostScript!fonts}\index{font!PostScript}\index{Adobe Type~1 + Font}\index{font!Adobe Type~1} format into its constituent filled +paths---the strokes---and store them in a picture variable. A glyph is +the visual representation of a character in a font. A +character\index{character}\index{font!character} is a certain +slot\index{slot}\index{font!slot} (index) in a font with an associated +meaning, e.g., the capital letter~``M'' or the exclamation mark. The +meaning of a slot is defined by the font +encoding\index{encoding}\index{font!encoding}. In general, the same +character is represented by different glyphs in different fonts. +Figure~\ref{glyphsample} shows some glyphs for the character at slot~103 +in the T1 encoding, i.e., the lower-case letter~``g''. All glyphs are +at the same nominal size. Note, how glyphs may extend beyond their +bounding box. +\begin{figure}[htp] + \centering + \setlength{\fboxsep}{0pt} + \setlength{\fboxrule}{.125pt} + \fontsize{56pt}{56pt}\selectfont + \newcommand*{\showglyph}[4]{% a glyph with its bounding box + \fbox{\usefont{#1}{#2}{#3}{#4}g}% + } + \makebox[0pt][c]{% base line + \rule{.7\textwidth}{.125pt}% + }% + \makebox[0pt][c]{% glyphs + \showglyph{T1}{lmr}{m}{n}\hspace{.3em} + \showglyph{T1}{qag}{m}{n}\hspace{.3em} + \showglyph{T1}{qpl}{m}{it}\hspace{.3em} + \showglyph{T1}{qzc}{m}{it}% + } + \caption{Different glyphs representing the same character.} + \label{glyphsample} +\end{figure} + +The glyphs of an Adobe Type~1 +font\index{PostScript!fonts}\index{font!PostScript}\index{Adobe Type~1 + Font}\index{font!Adobe Type~1} are composed of two types of contours: +Clockwise oriented contours add to the shape of a glyph and are filled +with black ink. Counter-clockwise oriented contours +erase\index{erasing} parts of other contours, i.e., make them +transparent again. To save the contours of a glyph in a picture, the +\verb|glyph|\index{glyph?\texttt{glyph}}\label{Dglyph} operator can be +used. There are two ways to identify a glyph in a font: +\begin{eqnarray*} + & \verb|glyph|\, \descr{numeric expression}\, \verb|of|\, + \descr{string expression}\\ + \noalign{\hbox{and}} + & \verb|glyph|\, \descr{string expression}\, \verb|of|\, + \descr{string expression}\rlap{\quad\mbox{.}} +\end{eqnarray*} + +If the first argument is a numeric expression, it has to be a slot +number between 0 and~255. Fractional slot numbers are rounded to the +nearest integer value. Slot numbers outside the allowed range trigger +an error. If the first argument is string, it has to be a CharString +name\index{CharString name} in the PostScript font's source file. A +CharString name is a unique text label for a glyph in a PostScript font +(a font encoding actually maps CharStrings to slots). This second +syntax can be used to address glyphs without having to think about font +encodings. The second argument to the \verb|glyph| operator is a string +containing a font name (section~\ref{text} has more on font names). + +The \verb|glyph| operator looks-up the font name in the font map to +determine the encoding and to find the font's PostScript source file. +It returns a picture consisting of the glyph's contour lines, explicitly +filled black and white in the greyscale color model according to the +rules laid out above. Additionally, the contours are sorted, such that +all black contours are drawn before white contours. The filling and +sorting is necessary for the picture to resembles the corresponding +glyph visually\footnote{Plain contours already carry enough information + to completely reconstruct a glyph, the orientation of a contour can be + computed from its cardinal and control points. MetaPost has a + \texttt{turningnumber}\index{turningnumber?\texttt{turningnumber}}\label{Dturningnumber} + primitive to do that.}, since Adobe Type~1 +fonts\index{PostScript!fonts}\index{font!PostScript}\index{Adobe Type~1 + Font}\index{font!Adobe Type~1} use a generalized variant of the +non-zero winding number fill rule\index{non-zero fill rule}\index{fill + rule!non-zero}\index{PostScript!fill rule}, which MetaPost doesn't +implement (MetaPost cannot handle non-contiguous paths). As a side +effect, the interiors of the erasing\index{erasing} contours are an +opaque white in the returned picture, while they were transparent in the +original glyph. One can think of erasing contours to be unfilled (see +p.~\pageref{Dunfill}). For instance, the following code saves the +contours of the lower case letter~``g'', bound to slot~103 in the OT1 +encoding\index{OT1 encoding}\index{encoding!OT1}, in the +Computer\index{Computer Modern Roman} Modern Roman font in a picture +variable: + +$$ +\begin{verbatim} +fontmapline "cmr10 CMR10 <cmr10.pfb"; +picture g; +g := glyph 103 of "cmr10"; +\end{verbatim} +$$ + +The \verb|glyph| operator returns an empty picture, if the +\texttt{.tfm}\index{tfm file?{\tt tfm} file}\index{files!tfm?{\tt tfm}} +or \texttt{.pfb}\index{pfb file?{\tt pfb} file}\index{files!pfb?{\tt + pfb}} file cannot be found, if the encoding given in the font map +cannot be found or the slot number is not covered by the encoding or if +the CharString name cannot be found. Note, while MetaPost delegates the +actual font handling to a rendering application for \verb|infont| and +\verb|btex| \ldots\ \verb|etex| blocks, the \verb|glyph| operator +directly operates on font ressources. For that reason, a font map entry +is mandatory for the font in question, given either by +\verb|fontmapline| or \verb|fontmapfile| (see +section~\ref{Dfontmapline}). + +In Figure~\ref{fig56}, the contours of the upper case letter~``\v{D}'' +in the Latin\index{Latin Modern Roman} Modern Roman font are saved in a +picture variable. The glyph is identified by its CharString name +``Dcaron''\index{Dcaron}. The code then iterates over all contours and +draws them together with their cardinal (black) and control points +(red). As it turns out, many of the control points coincide with +cardinal points in this glyph. + +\begin{figure}[htb] +$$ +\begin{verbatim} +fontmapfile "=lm-ec.map"; +beginfig(56); + picture q; + path p; + interim ahlength := 12bp; + interim ahangle := 25; + q := glyph "Dcaron" of "ec-lmr10" scaled .2; + for item within q: + p := pathpart item; + drawarrow p withcolor (.6,.9,.6) + withpen pencircle scaled 1.5; + for j=0 upto length p: + pickup pencircle scaled .7; + draw (point j of p -- precontrol j of p) + dashed evenly withcolor blue; + draw (point j of p -- postcontrol j of p) + dashed evenly withcolor blue; + pickup pencircle scaled 3; + draw precontrol j of p withcolor red; + draw postcontrol j of p withcolor red; + pickup pencircle scaled 2; + draw point j of p withcolor black; + endfor + endfor +endfig; +\end{verbatim} +\qquad +\mathcenter{\includegraphics{mpman-56.mps}} +$$ +\caption{Iterating over the contours of a glyph} +\label{fig56} +\end{figure} + +The contours in a picture returned by the \verb|glyph| operator are no +raw copies of the contours found in the font sources, but the +\verb|glyph| operator applies a number of transformations to them. +First, the direction of all contours is reversed, so that contours +filled black become counter-clockwise oriented (mathematically positive) +and contours filled white become clockwise oriented (mathematically +negative). Second, in an Adobe Type~1 +font\index{PostScript!fonts}\index{font!PostScript}\index{Adobe Type~1 + Font}\index{font!Adobe Type~1}, contours are in general closed by +repeating the starting point before applying the \verb|closepath| +operator\index{PostScript!closepath operator?\texttt{closepath} + operator}. The MetaPost representation of such a path would be: +$$ +z_0\verb|..|\mbox{\itshape controls}\verb|..|z_1\verb|..| \cdots +\verb|..|z_n\verb|..|\mbox{\itshape controls}\verb|..|z_0\verb|--cycle| +$$ +However, a more natural MetaPost representation of that path would be: +$$ +z_0\verb|..|\mbox{\itshape controls}\verb|..|z_1\verb|..| \cdots +\verb|..|z_n\verb|..|\mbox{\itshape controls}\verb|..cycle| +$$ +The \verb|glyph| operator transforms all paths into the latter +representation, i.e., the last point is removed, whenever it matches the +starting point. Finally, the picture returned by the \verb|glyph| +operator is scaled, such that one font design unit\index{font!design + unit} equals one PostScript +point\index{point!PostScript}\index{PostScript!point} (bp). A usual +font design unit is a thousandth part of the font design +size\index{font!design size}. Therefore, the returned picture will +typically have a height of around 1000bp. + +Converting a text into plain curves is part of a process oftentimes +called ``flattening\index{flattening}'' a document. During flattening, +all hinting information in fonts are lost. Hinting information aid a +rendering application in aligning certain parts of a glyph on a +low-resolution output device. A flattened text may therefore look +distorted on screen. In SVG output, all text is automatically +flattened, if the internal variable +\verb|prologues|\index{prologues?\texttt{prologues}} is set to~3 (see +section~\ref{Dprologues}). + + +\section{Macros} +\label{macros} + +As alluded to earlier, MetaPost has a set of automatically included +macros called the Plain macro package\index{Plain macros}, and some of +the commands discussed in previous sections are defined as macros +instead of being built into MetaPost. The purpose of this section is to +explain how to write such macros. + +Macros with no arguments are very simple. +A macro definition\index{replacement text?\tdescr{replacement text}}% +\index{def?\texttt{def}}\index{enddef?\texttt{enddef}} +$$ {\tt def}\, \descr{symbolic token}\, \hbox{\tt =}\, + \descr{replacement text}\, {\tt enddef} +$$ +makes the \tdescr{symbolic token} an abbreviation for the +\tdescr{replacement text}, where the \tdescr{replacement text} can be +virtually any sequence of tokens. For example, the Plain macro package +could almost define the {\tt fill} statement like +this\index{fill?\texttt{fill}}: +$$ \hbox{\tt def fill = addto currentpicture contour enddef} $$ + +Macros with arguments are similar, except they have formal parameters +that tell how to use the arguments in the \tdescr{replacement text}. +For example, the {\tt +rotatedaround}\index{rotatedaround?\texttt{rotatedaround}} macro is +defined like this: +$$\begin{verbatim} +def rotatedaround(expr z, d) = + shifted -z rotated d shifted z enddef; +\end{verbatim} +$$ +The {\tt expr}\index{expr?\texttt{expr}} in this definition means that +formal parameters {\tt z} and {\tt d} can be arbitrary expressions. +(They should be pair expressions but the MetaPost interpreter does not +immediately check for that.) + +Since MetaPost is an interpreted language, macros with arguments are a +lot like subroutines\index{subroutines}. MetaPost macros are often used +like subroutines, so the language includes programming concepts to +support this. These concepts include local variables, loops, and +conditional statements. + +\subsection{Grouping} +\label{grsec} + +Grouping in MetaPost is essential for functions\index{functions} and +local\index{variables!local}\index{locality} variables. The basic idea +is that a group is a sequence of statements possibly followed by an +expression with the provision that certain symbolic +tokens\index{tokens!symbolic} can have their old meanings restored at +the end of the group. If the group ends with an expression, the group +behaves like a function call that returns that expression. Otherwise, +the group is just a compound statement\index{compound statement}. The +syntax for a group +is\index{begingroup?\texttt{begingroup}}\index{endgroup?\texttt{endgroup}} +$$ {\tt begingroup}\, \descr{statement list}\, {\tt endgroup} $$ +or +$$ {\tt begingroup}\, \descr{statement list}\, \descr{expression}\, {\tt endgroup} +$$ +where a \tdescr{statement list} is a sequence of statements each +followed by a semicolon. A group with an \tdescr{expression} after the +\tdescr{statement list} behaves like a \tdescr{primary} in +Figure~\ref{syexpr} or like a \tdescr{numeric atom} in +Figure~\ref{synprim}. + +Since the \tdescr{replacement text} for the {\tt +beginfig}\index{beginfig?\texttt{beginfig}} macro starts with {\tt +begingroup} and the \tdescr{replacement text} for {\tt +endfig}\index{endfig?\texttt{endfig}} ends with {\tt endgroup}, each +figure in a MetaPost input file behaves like a group. This is what +allows figures can have local variables. We have already seen in +Section~\ref{vardecl} that variable names beginning with {\tt x} or {\tt +y} are local in the sense that they have unknown values at the beginning +of each figure and these values are forgotten at the end of each figure. +The following example illustrates how locality works: +\begin{eqnarray*} +&& \hbox{\tt x23 = 3.1;}\\ +&& \hbox{\tt beginfig(17);}\\ +&& \qquad \vdots\\ +&& \hbox{\tt y3a=1; x23=2;}\\ +&& \qquad \vdots\\ +&& \hbox{\tt endfig;}\\ +&& \hbox{\tt show x23, y3a;} +\end{eqnarray*} +The result of the {\tt show}\index{show?\texttt{show}} command is +$$\begin{verbatim} +>> 3.1 +>> y3a +\end{verbatim} +$$ +indicating that {\tt x23} has returned to its former value of {\tt 3.1} and +{\tt y3a} is completely unknown as it was at {\tt beginfig(17)}. + +The locality of {\tt x} and {\tt y} variables is achieved by the +statement\index{save?\texttt{save}}\label{Dsave} +$$ \hbox{\tt save x,y} $$ +in the \tdescr{replacement text} for {\tt +beginfig}\index{beginfig?\texttt{beginfig}}. In general, variables are +made local by the statement +$$ {\tt save}\, \descr{symbolic token list} $$ +where \tdescr{symbolic token list} is a comma-separated list of +tokens:\index{tokens!symbolic} +\begin{ctabbing} +$\tt \descr{symbolic token list} \rightarrow \descr{symbolic token}$\\ + $\tt \qquad \;|\; \descr{symbolic token}\hbox{\tt ,} + \descr{symbolic token list}$ +\end{ctabbing} +All variables whose names begin with one of the specified symbolic +tokens become unknown numerics and their present values are saved for +restoration at the end of the current group. If the {\tt save} +statement is used outside of a group, the original values are simply +discarded. + +The main purpose of the {\tt save} statement is to allow macros to use +variables without interfering with existing variables or variables in +other calls to the same macro. For example, the predefined macro {\tt +whatever}\index{whatever?\texttt{whatever}} has the \tdescr{replacement text} +$$ \hbox{\tt begingroup save ?; ? endgroup} $$ +This returns an unknown numeric quantity, but it is no longer called +question mark since that name was local to the group. Asking the name +via {\tt show\index{show?\texttt{show}} whatever} +yields\index{CAPSULE?\texttt{CAPSULE}} +$$ \hbox{\verb|>> %CAPSULE|}{\it nnnn} $$ +where {\it nnnn} is an identification number that is chosen when {\tt save} +makes the name question mark disappear. + +In spite of the versatility of {\tt save}, it cannot be used to make +local changes to any of MetaPost's internal variables\index{internal +variables}\index{variables!internal}. A statement such +as\index{linecap?\texttt{linecap}} +$$ \hbox{\tt save linecap} $$ +would cause MetaPost to temporarily forget the special meaning of this +variable and just make it an unknown numeric. If you want to draw one +dashed line with {\tt linecap:=butt} and then go back to the previous +value, you can use the {\tt +interim}\index{interim?\texttt{interim}}\label{Dinterm} statement as +follows: +\begin{eqnarray*} +&& \hbox{\tt begingroup interim linecap:=butt;}\\ +&& {\tt draw}\, \descr{path expression}\, \hbox{\tt dashed evenly; endgroup} +\end{eqnarray*} +This saves the value of the +internal variable\index{internal variables}\index{variables!internal} +{\tt linecap} and temporarily +gives it a new value without forgetting that {\tt linecap} is an internal +variable. The general syntax is +$$ {\tt interim}\, \descr{internal variable} \mathrel{\hbox{\tt:=}} + \descr{numeric expression} \;|\; \descr{string expression} +$$ + + +\subsection{Parameterized Macros} + +The basic idea behind parameterized macros is to achieve greater flexibility by +allowing auxiliary information to be passed to a macro. We have already seen +that macro definitions can have formal parameters that represent expressions +to be given when the macro is called. For instance a definition such as +$$ \hbox{\tt def rotatedaround(expr z, d) = } \descr{replacement text}\, + {\tt enddef} +$$ +allows the MetaPost interpreter to understand macro calls of the form +$$\tt rotatedaround\hbox{\tt (} + \descr{expression}\hbox{\tt ,} \descr{expression}\hbox{\tt )} +$$ + +The keyword {\tt expr}\index{expr?\texttt{expr}}\index{parameter!expr} +in the macro definition means that the parameters can be expressions of +any type. When the definition specifies {\tt (expr z, d)}, the formal +parameters {\tt z} and {\tt d} behave like variables of the appropriate +types. Within the \tdescr{replacement text}, they can be used in +expressions just like variables, but they cannot be redeclared or +assigned to. There is no restriction against unknown or partially known +arguments. Thus the definition\index{midpoint?\texttt{midpoint}} +$$ \hbox{\tt def midpoint(expr a, b) = (.5[a,b]) enddef} $$ +works perfectly well when {\tt a} and {\tt b} are unknown. An +equation such as +$$ \hbox{\tt midpoint(z1,z2) = (1,1)} $$ +could be used to help determine {\tt z1} and {\tt z2}. + +Notice that the above definition for {\tt midpoint} works for numerics, +pairs, or colors as long as both parameters have the same type. If for +some reason we want a {\tt +middlepoint}\index{middlepoint?\texttt{middlepoint}} macro that works +for a single path or picture, it would be necessary to do an {\tt +if}\index{if?\texttt{if}} test on the argument type. This uses the fact +there is a unary operator\index{path?\texttt{path}} +$$ {\tt path}\, \descr{primary} $$ +that returns a boolean result indicating whether its argument is a path. +Since the basic {\tt if} test has the +syntax\index{else?\texttt{else}}\index{fi?\texttt{fi}} +$$ {\tt if}\, \descr{boolean expression}\hbox{\tt:}\, \descr{balanced tokens}\, + \hbox{\tt else:}\, \descr{balanced tokens}\, {\tt fi} +$$ +where the \tdescr{balanced tokens}\index{balanced +tokens?\tdescr{balanced tokens}} can be anything that is balanced with +respect to {\tt if} and {\tt fi}, the complete {\tt +middlepoint}\index{middlepoint?\texttt{middlepoint}} macro with type test +looks like this: +$$\begin{verbatim} +def middlepoint(expr a) = if path a: (point .5*length a of a) + else: .5(llcorner a + urcorner a) fi enddef; +\end{verbatim} +$$ +The complete syntax for {\tt if} tests is shown in Figure~\ref{syif}. +It allows multiple {\tt if} tests like +$$ \hbox{\tt if $e_1$: \ldots\ else: if $e_2$: \ldots\ else: \ldots\ fi fi} $$ +to be shortened to\index{elseif?\texttt{elseif}} +$$ \hbox{\tt if $e_1$: \ldots\ elseif $e_2$: \ldots\ else: \ldots\ fi} $$ +where $e_1$ and $e_2$ represent boolean expressions. + +Note that {\tt if} tests are not statements and the \tdescr{balanced +tokens} in the syntax rules can be any sequence of balanced tokens even +if they do not form a complete expression or statement. Thus we could +have saved two tokens at the expense of clarity by defining {\tt +middlepoint} like this: +$$\begin{verbatim} +def middlepoint(expr a) = if path a: (point .5*length a of + else: .5(llcorner a + urcorner fi a) enddef; +\end{verbatim} +$$ + +\begin{figure}[htp] +\begin{ctabbing} +$\tt \descr{if test} \rightarrow if \descr{boolean expression} \hbox{\tt :} + \descr{balanced tokens} \descr{alternatives} fi$\\ +$\tt \descr{alternatives} \rightarrow \descr{empty}$\\ +$\tt \qquad \;|\; else\hbox{\tt :} \descr{balanced tokens}$\\ +$\tt \qquad \;|\; elseif \descr{boolean expression} \hbox{\tt :} + \descr{balanced tokens} \descr{alternatives}$ +\end{ctabbing} +\caption{The syntax for {\tt if} tests.} +\label{syif} +\end{figure} + +The real purpose of macros and {\tt if} tests is to automate repetitive +tasks and allow important subtasks to be solved separately. For +example, Figure~\ref{fig42} uses macros \verb|draw_marked|, +\verb|mark_angle|, and \verb|mark_rt_angle| to mark lines and angles +that appear in the figure. + +\begin{figure}[htp] +$$\begin{verbatim} +beginfig(42); +pair a,b,c,d; +b=(0,0); c=(1.5in,0); a=(0,.6in); +d-c = (a-b) rotated 25; +dotlabel.lft("a",a); +dotlabel.lft("b",b); +dotlabel.bot("c",c); +dotlabel.llft("d",d); +z0=.5[a,d]; +z1=.5[b,c]; +(z.p-z0) dotprod (d-a) = 0; +(z.p-z1) dotprod (c-b) = 0; +draw a--d; +draw b--c; +draw z0--z.p--z1; +draw_marked(a--b, 1); +draw_marked(c--d, 1); +draw_marked(a--z.p, 2); +draw_marked(d--z.p, 2); +draw_marked(b--z.p, 3); +draw_marked(c--z.p, 3); +mark_angle(z.p, b, a, 1); +mark_angle(z.p, c, d, 1); +mark_angle(z.p, c, b, 2); +mark_angle(c, b, z.p, 2); +mark_rt_angle(z.p, z0, a); +mark_rt_angle(z.p, z1, b); +endfig; +\end{verbatim} +\quad \mathcenter{\includegraphics{mpman-42.mps}} +$$ +\caption{MetaPost code and the corresponding figure} +\label{fig42} +\end{figure} + +The task of the +\verb|draw_marked|\index{draw_marked?\texttt{draw\_marked}} macro is to +draw a path with a given number of cross marks near its midpoint. A +convenient starting place is the subproblem of drawing a single cross +mark perpendicular to a path {\tt p} at some time {\tt t}. The +\verb|draw_mark|\index{draw_mark?\texttt{draw\_mark}} macro in +Figure~\ref{drawmarked} does this by first finding a vector {\tt dm} +perpendicular to~{\tt p} at~{\tt t}. To simplify positioning the cross +mark, the \verb|draw_marked| macro is defined to take an arc +length\index{arc length} {\tt a} along {\tt p} and use the {\tt +arctime}\index{arctime} operator to compute~{\tt t} + +With the subproblem of drawing a single mark out of the way, the +\verb|draw_marked| macro only needs to draw the path and call +\verb|draw_mark| with the appropriate arc length values. The +\verb|draw_marked| macro in Figure~\ref{drawmarked} uses {\tt n} +equally-spaced {\tt a} values centered on {\tt +.5*arclength~p}\index{arclength?\texttt{arclength}}. + +\begin{figure}[htp] +$$\begin{verbatim} +marksize=4pt; + +def draw_mark(expr p, a) = + begingroup + save t, dm; pair dm; + t = arctime a of p; + dm = marksize*unitvector direction t of p + rotated 90; + draw (-.5dm.. .5dm) shifted point t of p; + endgroup +enddef; + +def draw_marked(expr p, n) = + begingroup + save amid; + amid = .5*arclength p; + for i=-(n-1)/2 upto (n-1)/2: + draw_mark(p, amid+.6marksize*i); + endfor + draw p; + endgroup +enddef; +\end{verbatim} +$$ +\caption{Macros for drawing a path {\tt p} with {\tt n} cross marks.} +\label{drawmarked} +\end{figure} + +Since \verb|draw_marked| works for curved lines, it can be used to draw +the arcs that the +\verb|mark_angle|\index{mark_angle?\texttt{mark\_angle}} macro +generates. Given points {\tt a}, {\tt b}, and {\tt c} that define a +counter-clockwise angle at {\tt b}, the \verb|mark_angle| needs to +generate a small arc from segment {\tt ba} to segment {\tt bc}. The +macro definition in Figure~\ref{markangle} does this by creating an arc +{\tt p} of radius one and then computing a scale factor {\tt s} that +makes it big enough to see clearly. + +The \verb|mark_rt_angle|\index{mark_rt_angle?\texttt{mark\_rt\_angle}} +macro is much simpler. It takes a generic right-angle corner and uses +the {\tt zscaled}\index{zscaled?\texttt{zscaled}} operator to rotate it +and scale it as necessary. + +\begin{figure}[htp] +$$\begin{verbatim} +angle_radius=8pt; + +def mark_angle(expr a, b, c, n) = + begingroup + save s, p; path p; + p = unitvector(a-b){(a-b)rotated 90}..unitvector(c-b); + s = .9marksize/length(point 1 of p - point 0 of p); + if s<angle_radius: s:=angle_radius; fi + draw_marked(p scaled s shifted b, n); + endgroup +enddef; + +def mark_rt_angle(expr a, b, c) = + draw ((1,0)--(1,1)--(0,1)) + zscaled (angle_radius*unitvector(a-b)) shifted b +enddef; +\end{verbatim} +$$ +\caption{Macros for marking angles.} +\label{markangle} +\end{figure} + + +\subsection{Suffix and Text Parameters} + +Macro parameters need not always be expressions as in the previous +examples. Replacing the keyword {\tt expr} with {\tt +suffix}\index{suffix?\texttt{suffix}} or {\tt +text}\index{text?\texttt{text}} in a macro definition declares the +parameters to be variable names or arbitrary sequences of tokens. For +example, there is a predefined macro called {\tt +hide}\index{hide?\texttt{hide}} that takes a text +parameter\index{parameter!text} and interprets it as a sequence of +statements while ultimately producing an empty \tdescr{replacement +text}. In other words, {\tt hide} executes its argument and then gets +the next token as if nothing happened. Thus +$$ \hbox{\tt show hide(numeric a,b; a+b=3; a-b=1) a;} $$ +prints ``\verb|>> 2|.'' + +If the {\tt hide} macro were not predefined, it could be defined like this: +$$\begin{verbatim} +def ignore(expr a) = enddef; +def hide(text t) = ignore(begingroup t; 0 endgroup) enddef; +\end{verbatim} +$$ +The statements represented by the text parameter {\tt t} would be +evaluated as part of the group that forms the argument to {\tt ignore}. +Since {\tt ignore} has an empty \tdescr{replacement text}, expansion of +the {\tt hide} macro ultimately produces nothing. + +Another example of a predefined macro with a text parameter is {\tt +dashpattern}\index{dashpattern?\texttt{dashpattern}}. The definition of +{\tt dashpattern} starts +$$\begin{verbatim} +def dashpattern(text t) = + begingroup save on, off; +\end{verbatim} +$$ +then it defines {\tt on} and {\tt off} to be macros that create the desired +picture when the text parameter~{\tt t} appears in the replacement text. + +Text parameters are very general, but their generality sometimes gets in +the way. If you just want to pass a variable name to a macro, it is +better to declare it as a suffix parameter\index{parameter!suffix}. For +example,\index{incr?\texttt{incr}} +$$ \hbox{\verb|def incr(suffix $) = begingroup $:=$+1; $ endgroup enddef;|} $$ +defines a macro that will take any numeric variable, add one to it, and return +the new value. Since variable names can be more than one token long, +$$ \hbox{\tt incr(a3b)} $$ +is perfectly acceptable if {\tt a3b} is a numeric variable. Suffix +parameters are slightly more general than variable names because the +definition in Figure~\ref{syvar} allows a +\tdescr{suffix}\index{suffix?\tdescr{suffix}} to start with a +\tdescr{subscript}\index{subscript?\tdescr{subscript}}. + +Figure~\ref{fig45} shows how suffix and expr parameters can be used +together. The {\tt getmid}\index{getmid?\texttt{getmid}} macro takes a +path variable and creates arrays of points and directions whose names +are obtained by appending {\tt mid}, {\tt off}, and {\tt dir} to the +path variable. The {\tt joinup}\index{joinup?\texttt{joinup}} macro +takes arrays of points and directions and creates a path of length {\tt +n} that passes through each {\tt pt[i]} with direction {\tt d[i]} or +$-\hbox{\tt d[i]}$. + +\begin{figure}[htp] +$$\begin{verbatim} +def getmid(suffix p) = + pair p.mid[], p.off[], p.dir[]; + for i=0 upto 36: + p.dir[i] = dir(5*i); + p.mid[i]+p.off[i] = directionpoint p.dir[i] of p; + p.mid[i]-p.off[i] = directionpoint -p.dir[i] of p; + endfor +enddef; + +def joinup(suffix pt, d)(expr n) = + begingroup + save res, g; path res; + res = pt[0]{d[0]}; + for i=1 upto n: + g:= if (pt[i]-pt[i-1]) dotprod d[i] <0: - fi 1; + res := res{g*d[i-1]}...{g*d[i]}pt[i]; + endfor + res + endgroup +enddef; + +beginfig(45) +path p, q; +p = ((5,2)...(3,4)...(1,3)...(-2,-3)...(0,-5)...(3,-4) + ...(5,-3)...cycle) scaled .3cm shifted (0,5cm); +getmid(p); +draw p; +draw joinup(p.mid, p.dir, 36)..cycle; +q = joinup(p.off, p.dir, 36); +draw q..(q rotated 180)..cycle; +drawoptions(dashed evenly); +for i=0 upto 3: + draw p.mid[9i]-p.off[9i]..p.mid[9i]+p.off[9i]; + draw -p.off[9i]..p.off[9i]; +endfor +endfig; +\end{verbatim} +\quad \mathcenter{\includegraphics{mpman-45.mps}} +$$ +\caption{MetaPost code and the corresponding figure} +\label{fig45} +\end{figure} + +A definition that starts +$$ \hbox{\tt def joinup(suffix pt, d)(expr n) =} $$ +might suggest that calls to the {\tt joinup} macro should have two sets of +parentheses as in +$$ \hbox{\tt joinup(p.mid, p.dir)(36)} $$ +instead of +$$ \hbox{\tt joinup(p.mid, p.dir, 36)} $$ +In fact, both forms are acceptable. Parameters in a macro call can be +separated by commas or by {\tt )(} pairs. The only restriction is that +a text parameter\index{parameter!text} must be followed by a right +parenthesis. For instance, a macro {\tt foo} with one text parameter +and one expr parameter can be called +$$ \hbox{\tt foo(a,b)(c)} $$ +in which case the text parameter is ``{\tt a,b}'' and the expr parameter is +{\tt c}, but +$$ \hbox{\tt foo(a,b,c)} $$ +sets the text parameter to ``{\tt a,b,c}'' and leaves the MetaPost interpreter +still looking for the expr parameter. + + +\subsection{Vardef Macros} + +A macro definition can begin with {\tt +vardef}\index{vardef?\texttt{vardef}} instead of {\tt def}. Macros +defined in this way are called vardef macros. They are particularly +well-suited to applications where macros are being used like functions +or subroutines. The main idea is that a vardef macro is like a variable +of type ``macro.'' + +Instead of {\tt def} \tdescr{symbolic token}, a vardef macro begins +$$ {\tt vardef}\, \descr{generic variable} $$ +where a \tdescr{generic variable}\index{generic variable?\tdescr{generic +variable}} is a variable name with numeric subscripts replaced by the +generic subscript\index{subscript!generic} symbol {\tt +[]}\index{[]?\texttt{[]}!vardef macro?\texttt{vardef} macro}. In other +words, the name following {\tt +vardef} obeys exactly the same syntax as the name given in a variable +declaration. It is a sequence of tags and generic subscript symbols +starting with a tag, where a tag\index{tags} is a symbolic token that is +not a macro or a primitive operator as explained in +Section~\ref{vardecl}. + +The simplest case is when the name of a vardef macro consists of a +single tag. Under such circumstances, {\tt def} and {\tt vardef} +provide roughly the same functionality. The most obvious difference is +that {\tt begingroup}\index{begingroup?\texttt{begingroup}} and {\tt +endgroup}\index{endgroup?\texttt{endgroup}} are automatically inserted +at the beginning and end of the \tdescr{replacement text} of every +vardef macro. This makes the \tdescr{replacement text} a group so that +a vardef macro behaves like a subroutine or a function call. + +Another property of vardef macros is that they allow multi-token macro +names and macro names involving generic subscripts. When a vardef macro +name has generic subscripts, numeric values have to be given when the +macro is called. After a macro definition +$$ \hbox{\tt vardef a[]b(expr p) =}\, \descr{replacement text}\, + \hbox{\tt enddef;} +$$ +{\tt a2b((1,2))} and {\tt a3b((1,2)..(3,4))} are macro calls. But how +can the \tdescr{replacement text} tell the difference between {\tt a2b} +and {\tt a3b}? Two implicit suffix parameters\index{parameter!suffix} +are automatically provided for this purpose. Every vardef macro has +suffix parameters \verb|#@|\index{#@?\texttt{\#@}} and +\verb|@|\index{@?\texttt{@}}, where \verb|@| is the last token in the +name from the macro call and \verb|#@| is everything preceding the last +token. Thus \verb|#@| is {\tt a2} when the name is given as {\tt a2b} +and {\tt a3} when the name is given as {\tt a3b}. + +Suppose, for example, that the {\tt a[]b} macro is to take its argument +and shift it by an amount that depends on the macro name. The macro +could be defined like this: +$$ \hbox{\verb|vardef a[]b(expr p) = p shifted (#@,b) enddef;|} $$ +Then {\tt a2b((1,2))} means {\tt (1,2) shifted (a2,b)} +and {\tt a3b((1,2)..(3,4))} means +$$ \hbox{\tt ((1,2)..(3,4)) shifted (a3,b)}. $$ + +If the macro had been {\tt a.b[]}, \verb|#@| would always be {\tt a.b} +and the \verb|@| parameter would give the numeric subscript. Then {\tt +a@} would refer to an element of the array {\tt a[]}. Note that +\verb|@| is a suffix parameter, not an expr parameter, so an expression +like {\tt @+1} would be illegal. The only way to get at the numeric +values of subscripts in a suffix parameter\index{parameter!suffix} is by +extracting them from the string returned by the {\tt +str}\index{str?\texttt{str}}\label{Dstr} operator. This operator takes +a suffix and returns a string representation of a suffix. Thus {\tt str +@} would be \verb|"3"| in {\tt a.b3} and \verb|"3.14"| in {\tt a.b3.14} +or {\tt a.b[3.14]}. Since the syntax for a +\tdescr{suffix}\index{suffix?\tdescr{suffix}} in Figure~\ref{syvar} +requires negative subscripts to be in brackets, {\tt str @} returns {\tt +"[-3]"} in {\tt a.b[-3]}. + +The {\tt str} operator is generally for emergency use only. It is +better to use suffix parameters only as variable names or suffixes. The +best example of a vardef macro involving suffixes is the {\tt z} macro +that defines the {\tt z} convention\index{z convention?{\tt z} +convention}. The definition involves a special token +\verb|@#|\index{@#?\texttt{@\#}} that refers to the suffix following the +macro name: +$$ \hbox{\verb|vardef z@#=(x@#,y@#) enddef;|} $$ +This means that any variable name whose first token is {\tt z} is +equivalent to a pair of variables whose names are obtained by replacing +{\tt z} with {\tt x} and~{\tt y}. For instance, {\tt z.a1} calls the +{\tt z} macro with the suffix parameter \verb|@#| set to {\tt a1}. + +In general, +$$ {\tt vardef}\, \descr{generic variable} \hbox{\verb|@#|} $$ +is an alternative to {\tt vardef} \tdescr{generic variable} that causes the +MetaPost interpreter +to look for a suffix following the name given in the macro call and makes this +available as the \verb|@#| suffix parameter. + +To summarize the special features of vardef macros, they allow a broad +class of macro names as well as macro names followed by a special suffix +parameter. Furthermore, {\tt begingroup} and {\tt endgroup} are +automatically added to the \tdescr{replacement text} of a vardef macro. +Thus using {\tt vardef} instead of {\tt def} to define the {\tt +joinup}\index{joinup?\texttt{joinup}} macro in Figure~\ref{fig45} would +have avoided the need to include {\tt begingroup} and {\tt endgroup} +explicitly in the macro definition. + +In fact, most of the macro definitions given in previous examples could +equally well use {\tt vardef} instead of {\tt def}. It usually does not +matter very much which you use, but a good general rule is to use {\tt +vardef} if you intend the macro to be used like a function or a +subroutine. The following comparison should help in deciding when to +use {\tt vardef}. + +\begin{itemize} +\item Vardef macros are automatically surrounded by {\tt begingroup} +and {\tt endgroup}. +\item The name of a vardef macro can be more than one token long and it can +contain subscripts. +\item A vardef macro can have access to the suffix that follows the macro name +when the macro is called. +\item When a symbolic token is used in the name of a vardef macro it remains +a tag\index{tags} and can still be used in other variable names. Thus +{\tt p5dir} is a legal variable name even though {\tt dir} is a vardef +macro, but an ordinary macro such as {\tt ...}\index{...?\texttt{...}} +cannot be used in a variable name. (This is fortunate since {\tt +z5...z6} is supposed to be a path expression, not an elaborate variable +name). +\end{itemize} + + +\subsection{Defining Unary and Binary Macros} + +It has been mentioned several times that some of the operators and +commands discussed so far are actually predefined macros. These include +unary operators such as {\tt round}\index{round?\texttt{round}} and {\tt +unitvector}\index{unitvector?\texttt{unitvector}}, statements such as +{\tt fill}\index{fill?\texttt{fill}} and {\tt +draw}\index{draw?\texttt{draw}}, and binary operators such as {\tt +dotprod}\index{dotprod?\texttt{dotprod}} and {\tt +intersectionpoint}\index{intersectionpoint?\texttt{intersectionpoint}}. +The main difference between these macros and the ones we already know +how to define is their argument syntax. + +The {\tt round} and {\tt unitvector} macros are examples of what +Figure~\ref{syexpr} calls \tdescr{unary op}. That is, they are followed +by a primary expression. To specify a macro argument of this type, the +macro definition should look like this: +$$ \hbox{\tt vardef round primary u =}\, \descr{replacement text}\, + \hbox{\tt enddef;} +$$ +The {\tt u} parameter is an expr parameter\index{parameter!expr} and it can be +used exactly like the expr parameter defined using the ordinary +$$ \hbox{\tt (expr u)} $$ +syntax. + +As the {\tt round} example suggests, a macro can be defined to take a +\tdescr{secondary}\index{secondary?\tdescr{secondary}}, +\tdescr{tertiary}\index{tertiary?\tdescr{tertiary}}, or an +\tdescr{expression}\index{expression?\tdescr{expression}} parameter. +For example, the predefined definition of the {\tt fill} macro is +roughly\index{fill?\texttt{fill}} +$$ \hbox{\tt def fill expr c = addto currentpicture contour c enddef;} $$ + +It is even possible to define a macro to play the role of \tdescr{of +operator}\index{of operator?\tdescr{of operator}} in +Figure~\ref{syexpr}. For example, the {\tt direction +of}\index{direction of?\texttt{direction of}} macro has a definition of +this form: +$$ \hbox{\tt vardef direction expr t of p =}\, \descr{replacement text}\, + \hbox{\tt enddef;} +$$ + +Macros can also be defined to behave like binary operators. For instance, the +definition of the {\tt dotprod} macro has the +form\index{dotprod?\texttt{dotprod}}\index{primarydef?\texttt{primarydef}} +$$ \hbox{\tt primarydef w dotprod z =}\, \descr{replacement text}\, + \hbox{\tt enddef;} +$$ +This makes {\tt dotprod} a \tdescr{primary binop}\index{primary +binop?\tdescr{primary binop}}. Similarly, {\tt +secondarydef}\index{secondarydef?\texttt{secondarydef}} and {\tt +tertiarydef}\index{tertiarydef?\texttt{tertiarydef}} introduce +\tdescr{secondary binop}\index{secondary binop?\tdescr{secondary binop}} +and \tdescr{tertiary binop}\index{tertiary binop?\tdescr{tertiary +binop}} definitions. These all define ordinary macros, not vardef +macros; e.g., there is no ``{\tt primaryvardef}.'' + +Thus macro definitions can be introduced by {\tt def}, {\tt vardef}, +{\tt primarydef}, {\tt secondarydef}, or {\tt tertiarydef}. A +\tdescr{replacement text}\index{replacement text?\tdescr{replacement +text}} is any list of tokens that is balanced with respect to {\tt +def}-{\tt enddef} pairs where all five macro definition tokens are +treated like {\tt def} for the purpose of {\tt def}-{\tt enddef} +matching. + +The rest of the syntax for macro definitions is summarized in +Figure~\ref{symacro}. The syntax contains a few surprises. The macro +parameters can have a \tdescr{delimited part} and an \tdescr{undelimited +part}. Normally, one of these is \tdescr{empty}, but it is possible to +have both parts nonempty: +$$ \hbox{\tt def foo(text a) expr b =}\, \descr{replacement text}\, + \hbox{\tt enddef;} +$$ +This defines a macro {\tt foo} to take a text parameter in parentheses followed +by an expression. + +\begin{figure}[htp] +\begin{ctabbing} +$\tt \descr{macro definition} \rightarrow + \descr{macro heading} \hbox{\tt =} \descr{replacement text}\, enddef$\\ +$\tt \descr{macro heading} \rightarrow def\, \descr{symbolic token} + \descr{delimited part} \descr{undelimited part}$\\ +$\tt \qquad \;|\; vardef\, \descr{generic variable} \descr{delimited part} + \descr{undelimited part}$\\ +$\tt \qquad \;|\; vardef\, \descr{generic variable} \hbox{\tt @\#} + \descr{delimited part} \descr{undelimited part}$\\ +$\tt \qquad \;|\; \descr{binary def} \descr{parameter} + \descr{symbolic token} \descr{parameter}$\\ +$\tt \descr{delimited part} \rightarrow \descr{empty}$\\ +$\tt \qquad \;|\; \descr{delimited part} + \hbox{\tt (}\descr{parameter type} \descr{parameter tokens}\hbox{\tt )}$\\ +$\tt \descr{parameter type} \rightarrow expr \;|\; suffix \;|\; text$\\ +$\tt \descr{parameter tokens} \rightarrow \descr{parameter} \;|\; + \descr{parameter tokens}\hbox{\tt ,} \descr{parameter}$\\ +$\tt \descr{parameter} \rightarrow \descr{symbolic token}$\\ +$\tt \descr{undelimited part} \rightarrow \descr{empty}$\\ +$\tt \qquad \;|\; \descr{parameter type} \descr{parameter}$\\ +$\tt \qquad \;|\; \descr{precedence level} \descr{parameter}$\\ +$\tt \qquad \;|\; expr\, \descr{parameter}\, of\, \descr{parameter}$\\ +$\tt \descr{precedence level} \rightarrow primary \;|\; secondary \;|\; + tertiary$\\ +$\tt \descr{binary def} \rightarrow primarydef \;|\; secondarydef \;|\; + tertiatydef$ +\end{ctabbing} +\caption{The syntax for macro definitions} +\label{symacro} +\end{figure} + +The syntax also allows the \tdescr{undelimited part} to specify an +argument type of {\tt suffix}\index{suffix?\texttt{suffix}} or {\tt +text}\index{text?\texttt{text}}. An example of a macro with an +undelimited suffix parameter\index{parameter!suffix} is the predefined +macro {\tt incr}\index{incr?\texttt{incr}}\label{Dincr} that is actually +defined like this: +$$ \hbox{\verb|vardef incr suffix $ = $:=$+1; $ enddef;|} $$ +This makes {\tt incr} a function that takes a variable, increments it, +and returns the new value. Undelimited suffix parameters may be +parenthesized, so {\tt incr a} and {\tt incr(a)} are both legal if {\tt +a} is a numeric variable. There is also a similar predefined macro {\tt +decr}\index{decr?\texttt{decr}} that subtracts~1. + +Undelimited text parameters\index{parameter!text} run to the end of a +statement. More precisely, an undelimited text parameter is the list of +tokens following the macro call up to the first ``{\tt +;}\index{semicolon}'' or ``{\tt +endgroup}\index{endgroup?\texttt{endgroup}}'' or ``{\tt +end}\index{end?\texttt{end}}'' except that an argument containing ``{\tt +begingroup}'' will always include the matching ``{\tt endgroup}.'' An +example of an undelimited text parameter comes from the predefined macro +{\tt cutdraw}\index{cutdraw?\texttt{cutdraw}}\label{Dctdraw} whose +definition is +roughly\index{linecap?\texttt{linecap}}\index{butt?\texttt{butt}}\index{interim?\texttt{interim}} +$$\begin{verbatim} +def cutdraw text t = + begingroup interim linecap:=butt; draw t; endgroup enddef; +\end{verbatim} +$$ +This makes {\tt cutdraw} synonymous with {\tt draw} except for the {\tt +linecap} value. (This macro is provided mainly for compatibility with +\MF\index{metafont?\MF}.) + + +\section{Loops} + +Numerous examples in previous sections have used simple {\tt for} loops of the +form\index{loops}\index{for?\texttt{for}}\index{endfor?\texttt{endfor}} +$$ {\tt for}\, \descr{symbolic token}\, \hbox{\tt =}\, + \descr{expression}\, {\tt upto}\, \descr{expression}:\ + \descr{loop text}\, {\tt endfor} +$$ +It is equally simple to construct a loop that counts downward: just +replace {\tt upto} by {\tt +downto}\index{downto?\texttt{downto}}\label{Ddwnto} make the second +\tdescr{expression} smaller than the first. This section covers more +complicated types of progressions, loops where the loop counter behaves +like a suffix parameter, and ways of exiting from a loop. + +The first generalization is suggested by the fact that {\tt +upto}\index{upto?\texttt{upto}} is a predefined macro +for\index{step?\texttt{step}}\index{until?\texttt{until}} +$$ \hbox{\tt step 1 until} $$ +and {\tt downto}\index{downto?\texttt{downto}} is a macro for {\tt step +-1 until}. A loop begining +$$ \hbox{\tt for i=a step b until c} $$ +scans a sequence of {\tt i} values {\tt a}, ${\tt a}+{\tt b}$, ${\tt +a}+2{\tt b}$, \ldots, stopping before {\tt i} passes {\tt c}; i.e., the +loop scans {\tt i} values where ${\tt i}\le {\tt c}$ if ${\tt b}>0$ and +${\tt i}\ge {\tt c}$ if ${\tt b}<0$. For ${\tt b}=0$ the loop never +terminates, even if ${\tt a}={\tt c}$. + +It is best to use this feature only when the step size is an integer or +some number that can be represented exactly in fixed point +arithmetic\index{arithmetic} as a multiple of $1\over65536$. Otherwise, +error will accumulate and the loop index might not reach the expected +termination value. For instance, +$$ \hbox{\tt for i=0 step .1 until 1: show i; endfor} $$ +shows ten {\tt i} values the last of which is 0.90005. + +The standard way of avoid the problems associated with non-integer step +sizes is to iterate over integer values and then multiply by a scale +factor when using the loop index as was done in Figures \ref{fig1} +and~\ref{fig40}. + +Alternatively, the values to iterate over can be given explicitly. Any +sequence of zero or more expressions separated by commas can be used in +place of {\tt a step b upto c}. In fact, the expressions need not all +be the same type and they need not have known values. Thus +$$ \hbox{\tt for t=3.14, 2.78, (a,2a), "hello": show t; endfor} $$ +shows the four values listed. + +Note that the loop body in the above example is a statement followed by a +semicolon. It is common for the body of a loop to be one or more statements, +but this need not be the case. A loop is like a macro definition followed by +calls to the macro. The loop body can be virtually any sequence of tokens as +long as they make sense together. Thus, the (ridiculous) statement +$$ \hbox{\verb|draw for p=(3,1),(6,2),(7,5),(4,6),(1,3): p-- endfor cycle;|} $$ +is equivalent to +$$ \hbox{\verb|draw (3,1)--(6,2)--(7,5)--(4,6)--(1,3)--cycle;|} $$ +(See Figure~\ref{fig17} for a more realistic example of this.) + +If a loop is like a macro definition, the loop index is like an expr +parameter\index{parameter!expr}. It can represent any value, but it is +not a variable and it cannot be changed by an assignment +statement\index{assignment}. In order to do that, you need a {\tt +forsuffixes}\index{forsuffixes?\texttt{forsuffixes}} loop. A {\tt +forsuffixes} loop is a lot like a {\tt for} loop, except the loop index +behaves like a suffix parameter\index{parameter!suffix}. The syntax is +$$ {\tt forsuffixes}\, \descr{symbolic token}\, \hbox{\tt =}\, + \descr{suffix list}:\ \descr{loop text}\, {\tt endfor} +$$ +where a \tdescr{suffix list} is a comma-separated list of suffixes. If +some of the suffixes are \tdescr{empty}, the \tdescr{loop text} gets +executed with the loop index parameter set to the empty suffix. + +A good example of a {\tt forsuffixes} loop is the definition of the {\tt +dotlabels}\index{dotlabels?\texttt{dotlabels}} +macro\index{str?\texttt{str}}: +$$\begin{verbatim} +vardef dotlabels@#(text t) = + forsuffixes $=t: dotlabel@#(str$,z$); endfor enddef; +\end{verbatim} +$$ +This should make it clear why the parameter to {\tt dotlabels} has to be a +comma-separated list of suffixes. Most macros that accept variable-length +comma-separated lists +use them in {\tt for} or {\tt forsuffixes} loops in this fashion as values to +iterate over. + +When there are no values to iterate over, you can use a +{\tt forever}\index{forever?\texttt{forever}} loop: +$$ {\tt forever}\hbox{\tt :}\, \descr{loop text}\, {\tt endfor} $$ +To terminate such a loop when a boolean condition becomes true, use an exit +clause\index{exitif?\texttt{exitif}}: +$$ {\tt exitif}\, \descr{boolean expression} \hbox{\tt ;} $$ +When the MetaPost interpreter encounters an exit clause, it evaluates +the \tdescr{boolean expression} and exits the current loop if the +expression is true. If it is more convenient to exit the loop when an +expression becomes false, use the predefined macro {\tt +exitunless}\index{exitunless?\texttt{exitunless}}. + +Thus MetaPost's version of a {\bf while} loop is +$$ \hbox{\tt forever: exitunless}\, \descr{boolean expression} \hbox{\tt ;}\, + \descr{loop text}\, {\tt endfor} +$$ +The exit clause could equally well come just before {\tt endfor} or anywhere +in the \tdescr{loop text}. In fact any {\tt for}, {\tt forever}, or +{\tt forsuffixes} loop can contain any number of exit clauses. + +The summary of loop syntax shown in Figure~\ref{syloop} does not mention +exit clauses explicitly because a \tdescr{loop text} can be virtually +any sequence of tokens. The only restriction is that a \tdescr{loop +text} must be balanced with respect to {\tt for} and {\tt endfor}. Of +course this balancing process treats {\tt forsuffixes} and {\tt forever} +just like {\tt for}. + +\begin{figure}[htp] +\begin{ctabbing} +$\tt \descr{loop} \rightarrow \descr{loop header}\hbox{\tt :}\, + \descr{loop text} endfor$\\ +$\tt \descr{loop header} \rightarrow for\, \descr{symbolic token}\, + \hbox{\tt =}\, \descr{progression}$\\ +$\tt \qquad \;|\; for\, \descr{symbolic token}\, \hbox{\tt =}\, + \descr{for list}$\\ +$\tt \qquad \;|\; forsuffixes\, \descr{symbolic token}\, \hbox{\tt =}\, + \descr{suffix list}$\\ +$\tt \qquad \;|\; forever$\\ +$\tt \descr{progression} \rightarrow \descr{numeric expression}\, upto\, + \descr{numeric expression}$\\ +$\tt \qquad \;|\; \descr{numeric expression}\, downto\, + \descr{numeric expression}$\\ +$\tt \qquad \;|\; \descr{numeric expression}\, step\, + \descr{numeric expression}\, until\, \descr{numeric expression} $\\ +$\tt \descr{for list} \rightarrow \descr{expression} + \;|\; \descr{for list}\hbox{\tt ,}\, \descr{expression}$\\ +$\tt \descr{suffix list} \rightarrow \descr{suffix} + \;|\; \descr{suffix list}\hbox{\tt ,}\, \descr{suffix}$ +\end{ctabbing} +\caption{The syntax for loops} +\label{syloop} +\end{figure} + + +\section{Reading and Writing Files} +File access was one of the new language features introduced in version~0.60 +of the MetaPost language. A new operator +$$ {\tt readfrom}\ \descr{file name} $$\index{readfrom?\texttt{readfrom}}\label{Dreadfrom}% +returns a string giving the next line of input from the named +file\index{files!reading}. The \tdescr{file name} can be any primary +expression of type string. If the file has ended or cannot be read, the +result is a string consisting of a single null character. The preloaded +{\tt plain} macro package introduces the name +{\tt EOF}\index{EOF?\texttt{EOF}}\label{Deof} for this string. After +{\tt readfrom} has returned {\tt EOF}, additional reads from the same file +cause the file to be reread from the start. + +All files opened by \ttt{readfrom} that have not completely been read +yet are closed\index{files!closing} automatically when the program +terminates, but there exists a command +$${\tt closefrom}\ \descr{file name}$$% +\index{closefrom?\texttt{closefrom}}\label{Dclosefrom}% +to close files opened by {\tt readfrom} explicitly. It is wise to +manually close files you do not need to read completely (i.e. until {\tt + EOF} is returned) because otherwise such files will continue to use +internal resources and perhaps cause a \ttt{capacity exceeded!} error. + +The opposite of {\tt readfrom} is the command +$$ {\tt write}\ \descr{string expression}\ {\tt to}\ \descr{file name} $$% +\index{write to?\texttt{write to}}\label{Dwrite}% +This writes\index{files!writing} a line of text to the specified output file, +opening the file first if necessary. All such files are +closed\index{files!closing} automatically when the program terminates. They +can also be closed explicitly by using {\tt EOF}\index{EOF?\texttt{EOF}} +as the \tdescr{string expression}. The only way to tell if a {\tt write} +command has succeeded is to close the file and use {\tt readfrom} to look +at it. + + +\section{Utility Routines} + +\index{utility routines} +\index{mplib?\texttt{mplib}} +\index{metapost/base?\texttt{metapost/base}} + +This section describes some of the utility routines included in the +\texttt{mplib} directory of the development source hierarchy. Future +versions of this documentation may include more; meanwhile, please read +the source files, most have explanatory comments at the top. They are +also included in the MetaPost and larger \TeX\ distributions, typically +in a \texttt{texmf/metapost/base} directory. + + +\subsection{\texttt{TEX.mp}} + +\label{dTEX} +\index{TEX.mp?\texttt{TEX.mp}} +\index{labels, with variable text} +\index{string expressions, as labels} + +\texttt{TEX.mp} provides a way to typeset the text of a MetaPost string +expression. Suppose, for example, you need labels of the form $n_0$, +$n_1$, \ldots, $n_{10}$ across the $x$ axis. You can do this (relatively) +conveniently with \texttt{TEX.mp}, as follows: +$$\begin{verbatim} +input TEX; +beginfig(100) + last := 10; + for i := 0 upto last: + label(TEX("$n_{" & decimal(i) & "}$"), (5mm*i,0)); + endfor + ... +endfig; +\end{verbatim} +$$ +In contrast, the basic \texttt{btex} command (see p.\ \pageref{Dbtex}) +typesets verbatim text. That is, \texttt{btex~s~etex} typesets the +literal character `s'; \texttt{TEX(s)} typesets the value of the +MetaPost text variable~$s$. + +\index{LaTeX?\LaTeX!typesetting labels with} In version 0.9, +\texttt{TEX.mp} acquired two additional routines to facilitate using +\LaTeX\ to typeset labels: \texttt{TEXPRE} and \texttt{TEXPOST}. Their +values are remembered, and included before and after (respectively) each +call to \texttt{TEX}. Otherwise, each \texttt{TEX} call is effectively +typeset independently. \texttt{TEX} calls also do not interfere with +uses of {\tt verbatimtex}\index{verbatimtex?\texttt{verbatimtex}} (p.\ +\pageref{Dverbatimtex}). + +Here's the same example as above, using the \LaTeX\ commands \verb|\(| +and \verb|\)|: + +$$\begin{verbatim} +input TEX; +TEXPRE("%&latex" & char(10) & "\documentclass{article}\begin{document}"); +TEXPOST("\end{document}"); +beginfig(100) + last := 10; + for i := 0 upto last: + label(TEX("\( n_{" & decimal(i) & "} \)"), (5mm*i,0)); + endfor + ... +endfig; +\end{verbatim} +$$ +Explanation: +\begin{itemize} + +\item +The \texttt{\%\&latex}\index{\%?\texttt{\%}!magic comment!\%\&?\texttt{\%\&}} causes \LaTeX\ to be invoked instead of \TeX. +(See below, also.) Web2C- and MiKTeX-based \TeX\ implementations, at +least, understand this \texttt{\%\&} specification; see, e.g., the Web2C +documentation for details, \url{http://tug.org/web2c}. (Information on +how to do the same with other systems would be most welcome.) + +\item +The \texttt{char(10)} puts a newline (ASCII character code 10, decimal) +in the output. + +\item +The \verb|\documentclass...| is the usual way to start a \LaTeX\ +document. + +\item +The \verb|TEXPOST("\end{document}")| is not strictly necessary, due to +the behavior of \texttt{mpto}, but it is safer to include it. + +\end{itemize} + +Unfortunately, \TeX\ \verb|\special| instructions vanish in this +process. So it is not possible to use packages such as \texttt{xcolor} +and \texttt{hyperref}. + +In case you're curious, these routines are implemented very simply: they +write \texttt{btex} commands to a temporary file and then use +\texttt{scantokens} (p.\ \pageref{Dscantokens}) to process it. The +\texttt{makempx} mechanism (p.\ \pageref{Dmakempx}) does all the work of +running \TeX. + +The \verb|%&| magic on the first line is not the only way to specify +invoking a different program than (plain) \TeX. It has the advantage of +maximum flexibility: different \texttt{TEX} constructs can use different +\TeX\ processors. But at least two other methods are possible: + +\begin{itemize} +\item Set the environment variable \texttt{TEX} to \texttt{latex}---or +whatever processor you want to invoke. (To handle \ConTeXt\ fragments, +\ttt{texexec} could be used.) This might be convenient when writing a +script, or working on a project that always requires \texttt{latex}. + +\item Invoke MetaPost with the command-line option \ttt{-tex=latex} (or +whatever processor, of course). This might be useful from a Makefile, +or just a one-off run. +\end{itemize} + + +\section{Another Look at the MetaPost Workflow} +\label{workflow2} + +\index{workflow} + +In Section~\ref{workflow} we already had a brief look at how MetaPost +compiles input files and generates output files. This section contains +some more information and discusses internal variables that can be used +to control MetaPost's run-time behavior, previewing PostScript output, +debugging MetaPost code, and importing MetaPost graphics into +third-party applications. + +\subsection{Customizing Run-Time Behavior} + +\index{runtime behavior!customize} + +MetaPost knows and obeys a number of internal\index{internal + variables}\index{variables!internal} variables that have no direct +impact on drawing commands, but can be used to customize the way the +MetaPost compiler processes input files. The following paragraphs +describe those variables (in no particular order). + +\paragraph{Date and Time} + +MetaPost provides a number of internal numeric variables that store the +date and time a job was started, i.e., the MetaPost executable was +called on the command-line. Variables +\texttt{year}\index{year?\texttt{year}}\label{Dyear}, +\texttt{month}\index{month?\texttt{month}}\label{Dmonth}, +\texttt{day}\index{day?\texttt{day}}\label{Dday}, +\texttt{hour}\index{hour?\texttt{hour}}\label{Dhour}, and +\texttt{minute}\index{minute?\texttt{minute}}\label{Dminute} should be +self-explanatory. Variable +\texttt{time}\index{time?\texttt{time}}\label{Dtime} returns the number +of minutes past midnight, since the job was started, i.e., +$\texttt{time} = 60*\texttt{hour} + \texttt{minute}$. + +\paragraph{Output File Names} + +As discussed in Section~\ref{workflow}, by default, every +\verb|beginfig| \ldots\ \verb|endfig| group in an input file corresponds +to an output file that follows the naming scheme +\texttt{\tdescr{jobname}.\tdescr{n}}. That is, all files have varying +numeric file extensions. MetaPost provides a template mechanism that +allows for more flexible output file names. The template mechanism uses +\texttt{printf}-style escape sequences that are re-evaluated at ship-out +time, i.e., before each figure is written to disk. + +To configure the output file naming scheme a string containing the +corresponding escape sequences has to be assigned to the internal string +variable +\verb|outputtemplate|\index{outputtemplate?\texttt{outputtemplate}}\label{Doutputtemplate}. +The escape sequences provided are listed in +table~\ref{tab:outputtemplate}. As an example, if this code is saved in +a file \texttt{fig.mp}, +$$ +\begin{verbatim} +outputtemplate := "%j-%c.mps"; +beginfig(1); + drawdot origin; +endfig; +end +\end{verbatim} +$$ +it will create the output file \texttt{fig-1.mps} instead of +\texttt{fig.1}. The file extension \texttt{mps}\index{mps file?{\tt + mps} file}\index{files!mps?{\tt mps}} is conventionally chosen for +MetaPost's PostScript output (see Section~\ref{mpimport}). For SVG and +PNG output one would want to use file extensions \texttt{svg}\index{svg + file?{\tt svg} file}\index{files!svg?{\tt svg}} and +\texttt{png}\index{png file?{\tt png} file}\index{files!png?{\tt png}} +instead. + +\begin{table} + \centering + \begin{tabular}{|>{\ttfamily}l|l|>{\ttfamily}l|} + \hline + \multicolumn1{|c|}{Escape sequence} & \multicolumn1{c|}{Meaning} & \multicolumn1{c|}{Alternative}\\\hline + \%\%\index{\%?\texttt{\%}!outputtemplate escape sequence?\texttt{outputtemplate} escape sequence!\%\%?\texttt{\%\%}} & percent sign &\\ + \%\{\tdescr{internal variable}\}\index{\%?\texttt{\%}!outputtemplate + escape sequence?\texttt{outputtemplate} escape sequence!\%\{...\}?\texttt{\%\{\tdescr{internal variable}\}}} & evaluate internal variable &\\ + \%j\index{\%?\texttt{\%}!outputtemplate escape sequence?\texttt{outputtemplate} escape sequence!\%j?\texttt{\%j}} & current jobname & \%\{jobname\}\\ + \%c\index{\%?\texttt{\%}!outputtemplate escape sequence?\texttt{outputtemplate} escape sequence!\%c?\texttt{\%c}} & charcode value (\texttt{beginfig} argument) & \%\{charcode\}\\ + \%y\index{\%?\texttt{\%}!outputtemplate escape sequence?\texttt{outputtemplate} escape sequence!\%y?\texttt{\%y}} & current year & \%\{year\}\\ + \%m\index{\%?\texttt{\%}!outputtemplate escape sequence?\texttt{outputtemplate} escape sequence!\%m?\texttt{\%m}} & month (numeric) & \%\{month\}\\ + \%d\index{\%?\texttt{\%}!outputtemplate escape sequence?\texttt{outputtemplate} escape sequence!\%d?\texttt{\%d}} & day of the month & \%\{day\}\\ + \%H\index{\%?\texttt{\%}!outputtemplate escape sequence?\texttt{outputtemplate} escape sequence!\%H?\texttt{\%H}} & hour & \%\{hour\}\\ + \%M\index{\%?\texttt{\%}!outputtemplate escape sequence?\texttt{outputtemplate} escape sequence!\%M?\texttt{\%M}} & minute & \%\{minute\}\\ + \hline + \end{tabular} + \caption{Allowed escape sequences for \ttt{outputtemplate}} + \label{tab:outputtemplate} +\end{table} + +In single-letter escape sequences referring to internal numerics, the +corresponding value is rounded to the nearest integer before it is +converted to a string expression. In such escape sequences, a number +from the range 0 to~99 can optionally be placed directly after \verb|%| +that determines the minimum number of digits in the resulting string +expression, like \verb|%2m|. If the decimal representation of the +internal variable requires more digits, actual string length will exceed +the requested length. If less digits are required, the string is padded +to the requested length with zeros from left. + +In single-letter escape sequences referring to internal string +variables, like \verb|%j|, and in the \verb|%{...}| escape sequence, +neither rounding nor zero-padding take place. + +For backwards compatibility, the +\verb|%c|\index{\%?\texttt{\%}!outputtemplate escape + sequence?\texttt{outputtemplate} escape sequence!\%c?\texttt{\%c}} +escape sequence is handled special. If the result of rounding the +charcode value is negative, \verb|%c| evaluates to the string \verb|ps|. +This transformation can be bypassed by using \verb|%{charcode}| instead +of \verb|%c|. But note, that this bypasses rounding and zero-padding as +well. + +The template mechanism can also be used for naming graphic files +individually, yet keeping all sources in one file. Collecting, e.g., +different diagram sources in a single file \texttt{fig.mp}, it might be +easier to recall the correct diagram names in a \TeX\ document than with +numbered file names. Note, the argument to \verb|beginfig| is not +relevant as long as there's no \verb|%c| pattern in the file name +template string. +$$ +\begin{verbatim} +outputtemplate := "fig-quality.mps"; +beginfig(1); + ... +endfig; + +outputtemplate := "fig-cost-vs-productivity.mps"; +beginfig(2); + ... +endfig; +\end{verbatim} +$$ + +To ensure compatibility with older files, the default value of +\verb|outputtemplate| is \verb|%j.%c|. If you assign an empty string, +it will revert to that default. MetaPost versions~1.000 to~1.102 used a +different template mechanism, see Section~\ref{Dfilenametemplate} for +more information. + +During \texttt{shipout}\index{shipout?\texttt{shipout}}, the name of the +output file to be written is stored in an internal string variable +\texttt{outputfilename}\index{outputfilename?\texttt{outputfilename}}\label{Doutputfilename}. +It remains available until the next \texttt{shipout} command. The +variable is initially empty. + +\paragraph{Output Format} + +MetaPost can generate graphics in three output formats: + +\begin{itemize} +\item Encapsulated PostScript\index{PostScript!structured} + (EPSF\index{EPSF}), +\item Scalable Vector Graphics (SVG\index{SVG}) following version~1.1 of + the SVG specification~\cite{w3c:svg1.1} (since MetaPost version + 1.200), +\item Portable Network Graphics (PNG), a losslessly compressing bitmap + format (since MetaPost version 1.800). +\end{itemize} +By default, MetaPost outputs PostScript files---hence the name MetaPost. +The output format can be changed by assigning values \verb|"svg"| or +\verb|"png"| to the internal string variable\index{internal + variables}\index{variables!internal} +\verb|outputformat|\index{outputformat?\texttt{outputformat}}\label{Doutputformat}: +$$ +\begin{verbatim} +outputformat := "svg"; +\end{verbatim} +$$ +Other values make MetaPost fall back to PostScript output. Variable +\verb|outputformat| is case-sensitive, so assigning it the string +\verb|"SVG"| enables PostScript output, too. Default value of variable +\verb|outputformat| is \verb|"eps"|. + +\paragraph{Bitmap output} To create bitmap output in the PNG format, +MetaPost utilizes the Cairo\index{Cairo} \cite{lib:cairo} graphics +library.\footnote{The Cairo library version is printed when MetaPost is + run with the \texttt{-version} command-line switch.} Bitmap +conversion can be controlled from within MetaPost using three internal +variables: \texttt{outputformatoptions}, \texttt{hppp}, and +\texttt{vppp}. + +\begin{table} + \centering + \begin{tabular}{|>{\ttfamily}l|>{\ttfamily}l|l|} + \hline + \multicolumn1{|c|}{Key} & \multicolumn1{c|}{Values} & \multicolumn1{c|}{Meaning}\\\hline + format & + rgba\index{rgba?\texttt{rgba}|see{\texttt{outputformatoptions}, + \texttt{format}}} & RGB color space\index{PNG!color space!RGBA} + with alpha channel\index{PNG!alpha channel}\\ + & rgb\index{rgb?\texttt{rgb}|see{\texttt{outputformatoptions}, + \texttt{format}}} & RGB color space\index{PNG!color space!RGB}\\ + & graya\index{graya?\texttt{graya}|see{\texttt{outputformatoptions}, + \texttt{format}}} & gray scale color space\index{PNG!color + space!gray scale with alpha} with alpha channel\index{PNG!alpha + channel}\\ + & gray\index{gray?\texttt{gray}|see{\texttt{outputformatoptions}, + \texttt{format}}} & gray scale color space\index{PNG!color + space!gray scale}\\ + \hline + antialias & + none\index{none?\texttt{none}|see{\texttt{outputformatoptions}, + \texttt{antialias}}} & no anti aliasing\index{PNG!anti + aliasing}\\ + & fast\index{fast?\texttt{fast}|see{\texttt{outputformatoptions}, + \texttt{antialias}}} & fastest anti aliasing algorithm\\ + & good\index{good?\texttt{good}|see{\texttt{outputformatoptions}, + \texttt{antialias}}} & better quality, but slower\\ + & best\index{best?\texttt{best}|see{\texttt{outputformatoptions}, + \texttt{antialias}}} & best quality, slowest\\ + \hline + \end{tabular} + \caption{Valid keys and values in variable \texttt{outputformatoptions}.} + \label{tab:outputformatoptions} +\end{table} + +Variable +\texttt{outputformatoptions}\index{outputformatoptions?\texttt{outputformatoptions}}\label{Doutputformatoptions} +is a string containing a list of \tdescr{key}\verb|=|\tdescr{value} +pairs separated by spaces (no other spaces are allowed). Key +\texttt{format}\index{format?\texttt{format}|see{outputformatoptions, + \texttt{format}}}\index{outputformatoptions?\texttt{outputformatoptions}!format?\texttt{format}} +determines color space of the written PNG file. Key +\texttt{antialias}\index{antialias?\texttt{antialias}|see{outputformatoptions, + \texttt{antialias}}}\index{outputformatoptions?\texttt{outputformatoptions}!antialias?\texttt{antialias}} +determines what level of anti aliasing\index{anti aliasing|see{PNG, anti + aliasing}}\index{PNG!anti aliasing} is applied during vector graphic +to bitmap conversion. The set of accepted values and their meanings can +be found in table~\ref{tab:outputformatoptions}. An assignment that +would match the compiled-in default setup would look like + +$$ +\begin{verbatim} +outputformatoptions := "format=rgba antialias=fast"; +\end{verbatim} +$$ +Keys not given in an assignment to \texttt{outputformatoptions} are +reset to their default value. By default, this variable is empty. + +PNG files have a transparent background\index{background in PNG output} +if output color space provides an alpha channel\index{alpha + channel|see{PNG, alpha channel}}\index{PNG!alpha channel} +(\texttt{format}\index{outputformatoptions?\texttt{outputformatoptions}!format?\texttt{format}} +is \texttt{rgba} or \texttt{graya}). Otherwise background becomes +white. Color channels have a bit-depth of~8 in output. Colors not +supported by the output format, e.g., CMYK colors, are transformed to a +color with a similar visual impression. Here's how colors are +transformed during bitmap conversion. Let's recall that color +components in a MetaPost picture are in the range $[0;1]$ (see the +discussion of color types in Section~\ref{datatypes}). Whatever input +and output color spaces are used, all colors found in a picture are +initially converted to RGB color space. A gray scale color with +intensity $i$ is converted to an RGB color with all components set +to~$i$. RGB colors are left unchanged. A CMYK color with components +$(c,m,y,k)$ is converted to an RGB color with components $(r,g,b)$ using +equations +\begin{eqnarray} + r &=& 1 - k - c\\ + g &=& 1 - k - m\\ + b &=& 1 - k - y +\end{eqnarray} +with results clipped to the range $[0;1]$. If requested by the output +format (\texttt{gray} or \texttt{graya}), such a color is further +converted to a gray color with intensity +\begin{eqnarray} +j = 0.2126 \cdot r + 0.7152 \cdot g + 0.0722 \cdot b +\end{eqnarray} + +Note, colors are exact in PNG output if input and output color spaces +are compatible, i.e., both are RGB or gray scale or output in RGB color +space contains only gray scale colors. Users that care about color +conversion can apply the necessary transformations explicitly in a +\texttt{for within~\tdescr{\mbox{picture}}}\index{for within?\texttt{for + within}} loop inside +\texttt{extra\_endfig}\index{extra_endfig?\texttt{extra\_endfig}} (see +Section~\ref{Dforwithin} and Appendix~\ref{Dxefig}). MetaPost has no +built-in color management support. The built-in conversions are +provided just as a convenience. + +Resolution of PNG output is always 72~dpi\index{dpi}\index{units!dpi} +(dots per inch). Two internal variables +\texttt{hppp}\index{hppp?\texttt{hppp}}\label{Dhppp} and +\texttt{vppp}\index{vppp?\texttt{vppp}}\label{Dvppp} are used by the PNG +backend to decide on the scale of the generated bitmap. These two +variables have already been present in \MF\ and have been revived when +MetaPost acquired the bitmap backend in version 1.800. But there's a +catch: In \MF, variables \texttt{hppp} and \texttt{vppp} refer to +horizontal and vertical scale in \emph{pixels per + point}\index{units!pixels per point} and values larger than~1 result +in output of larger dimensions. In MetaPost, the meaning of both +variables is the other way around. They refer to horizontal and +vertical scale in \emph{points per pixel}\index{units!points per pixel} +and values larger than~1 result in output of smaller dimensions. +Default value for both variables is $1.0$, i.e., one MetaPost point per +pixel. + +\paragraph{PostScript Dictionary} + +For PostScript output, MetaPost can define a dictionary of abbreviations +of the PostScript commands, e.g., \verb|l| instead of \verb|lineto|, to +reduce the size of output files. Setting the internal variable +\texttt{mpprocset}\index{mpprocset?\texttt{mpprocset}}\label{Dmpprocset} +to~1 makes MetaPost create an extended preamble setting-up the +dictionary. Default value of variable \texttt{mpprocset} is~0, that is, +no dictionary is used. For SVG and PNG output, variable +\texttt{mpprocset} is not relevant. + +\paragraph{Version Number} + +The version number of the MetaPost compiler can be determined from +within a MetaPost program via the predefined constant string +\texttt{mpversion}\index{mpversion?\texttt{mpversion}}\label{Dmpversion} +(since version~0.9). For instance the following code +$$ +\begin{verbatim} +message "mp = " & mpversion; +\end{verbatim} +$$ +writes +$$ +\begin{verbatim}[commandchars=\\\{\}] +mp = \mpversion +\end{verbatim} +$$ +to the console and the transcript file. Variable \texttt{mpversion} can +be used to execute code depending on the MetaPost version like this: +$$ +\begin{verbatim}[commandchars=\\\{\}] +if unknown mpversion: string mpversion; mpversion := "0.000"; fi +if scantokens(mpversion) < 1.200: + errmessage "MetaPost v1.200 or later required (found v" & mpversion & ")"; +else: + \tdescr{code} +fi +\end{verbatim} +$$ +The first line is optional and only added to handle ancient MetaPost +versions gracefully that don't even know about variable +\textrm{mpversion} (prior to v0.9). The second test does the actual +work. + +The version number is also written to output files and the transcript +file. For PostScript output, the version number can be found in the +\texttt{Creator}\index{Creator comment in PostScript + output?\texttt{Creator} comment in PostScript output|see{PostScript, + \texttt{Creator} comment}}\index{PostScript!Creator + comment?\texttt{Creator} comment} comment. SVG files contain a simple +comment line near the beginning of the file. For PNG output, the +version number can be found in a text chunk with keyword +\texttt{Software}\index{Software keyword in PNG text + chunk?\texttt{Software} keyword in PNG text chunk|see{PNG, text + chunk}}\index{text chunk|see{PNG, text chunk}}\index{PNG!text + chunk}. The transcript\index{files!transcript} file starts with a +banner line that identifies the version\index{version number} of the +MetaPost compiler. + +\subsection{Previewing PostScript Output} +\label{preview} +\index{preview!PostScript} + +Previewing MetaPost's PostScript output is not difficult, but there are +some catches that one should know about. This section deals with the +following questions: How can graphics be clipped to their true bounding +box in the PostScript viewer application? Why are my text labels +rendered with an ugly font (or not at all) and how to avoid that? How +can several graphics be combined into a multi-page document that can be +previewed within one instance of the viewer application? + +\subsubsection{Bounding Box} +\index{bounding box} +\index{PostScript!bounding box} + +With default settings, MetaPost writes very much stripped-down +PostScript code, containing only the bare graphics code, but no other +ressources, like fonts etc. The PostScript code is somewhat deficient, +because it fails to correctly identify as Encapsulated PostScript +(EPSF\index{EPSF}) in the header. Note, Encapsulated PostScript files +don't have an associated page size, but provide bounding box +information, because they are meant for inclusion into other documents. +Instead MetaPost output wrongly pretends to be full PostScript +(PS\index{PS}), which it is not. + +This is just fine for including MetaPost graphics in, say, \TeX\ +documents (see Section~\ref{mpimport}), but some PostScript viewers have +difficulties rendering those PostScript files correctly. As an example, +because of the wrong ``PS'' header, GSview\index{GSview}---not knowing +better---ignores bounding box information and then clips all contents to +a (configurable) page size. Graphic elements laying outside those fixed +page boundaries are therefore not visible, e.g., when they have negative +coordinates. + +To avoid such situations, the first rule when previewing MetaPost's +PostScript output is to put the line +$$ +\begin{verbatim} +prologues := 2; +\end{verbatim} +\index{prologues?\texttt{prologues}} +$$ +before the first \verb|beginfig| in MetaPost input files (see the +discussion about \texttt{prologues} in Section~\ref{Dprologues}). That +way, MetaPost's PostScript output correctly identifies as Encapsulated +PostScript and viewer applications should always obey the file's +bounding box for on-screen rendering. + +A workaround for MetaPost's deficient default PostScript code that can +sometimes be seen is to move the lower left corner of a figure to the +origin as a last operation by saying +$$ +\begin{verbatim}[commandchars=\\\{\}] +\color{gray}currentpicture := currentpicture shifted -llcorner currentpicture; +\end{verbatim} +\index{currentpicture?\texttt{currentpicture}} +\index{llcorner?\texttt{llcorner}} +$$ +before \verb|endfig|. But this doesn't prevent from clipping on the +right and upper page boundaries. Additionally, the line is required for +all figures, cluttering source code, and it alters all coordinates in +PostScript output, which might complicate debugging. Applying such a +manual transformation is therefore not recommended (which is why the +line is grayed out). Instead, users are advised to adjust +\texttt{prologues} once in the preamble of the input file and enable +clipping to the bounding box in the PostScript viewer. For +GSview\index{GSview}, that can be done by activating \texttt{Options} +$\rightarrow$ \texttt{EPS Clip} and optionally \texttt{Options} +$\rightarrow$ \texttt{Show Bounding Box} for verification. + +\subsubsection{Text Labels} + +Another popular previewing issue concerns graphics that contain text +labels. An observation MetaPost users can often make is that text +labels in graphics are rendered with wrong fonts, wrong glyphs, and +sometimes even not at all. The reason is that with default settings, +again, MetaPost's PostScript output is deficient, in that it uses a +simple, non-standard way to declare what fonts are used in a graphic. +Setting variable \texttt{prologues} to~2, as shown in the previous +section, makes MetaPost generate more complex PostScript code to declare +all needed PostScript\index{PostScript!fonts} fonts and embed the +necessary encoding information. If the PostScript viewer can provide +the requested fonts, this might be sufficient to get text labels +rendered correctly. If you still observe wrong or missing glyphs you +should put the line +$$ +\begin{verbatim} +prologues := 3; +\end{verbatim} +\index{prologues?\texttt{prologues}} +$$ +into the preamble of the input file. That way, MetaPost embeds the used +PostScript\index{PostScript!fonts} fonts into the output file so that +they are always available (see the discussion about \texttt{prologues} +in Section~\ref{Dprologues}). Note, this might enlarge the size of +output files considerably. Additionally, fonts might be embedded +multiple times when several graphics using the same fonts are included +into a document. For that reason, it is recommended to reset variable +\texttt{prologues} to~0 before finally including MetaPost graphics into +external documents. + +\subsubsection{Proof Sheets} +\index{proof sheets} + +If you have lots of figures in a source file and need to preview many of +them at the same time, opening every graphic in a new instance of the +viewer application and switching between them back and forth can get +cumbersom. An alternative is to collect all graphics generated from a +MetaPost input file in a proof sheet, a multi-page document, that can be +previewed and navigated in a single instance of the viewer application. +The MetaPost distribution contains two (plain) \TeX\ scripts, +\texttt{mproof.tex} and \texttt{mpsproof.tex}, that help with the latter +approach. + +\paragraph{\texttt{mproof.tex}} +\index{mproof.tex?\texttt{mproof.tex}} + +To write a proof sheet for MetaPost output, call \texttt{mproof.tex} as +$$ +\begin{verbatim}[commandchars=\\\{\}] +tex mproof \tdescr{MetaPost output files} +\end{verbatim} +$$ +Then process the resulting \texttt{.dvi}\index{dvi file?{\tt dvi} + file}\index{files!dvi?{\tt dvi}} file as usual. That way, there's no +need to care about different settings of variable +\texttt{prologues}\index{prologues?\texttt{prologues}}, since in proof +sheets MetaPost graphics are already embedded. + +Note, the parameters after \texttt{mproof} are an explicit list of +MetaPost output files, possibly generated from different input files. +On shells that support POSIX\index{shell patterns}\index{POSIX!shell + patterns} shell patterns, these can be used to avoid typing a long +list of files. As an example, for a file \texttt{fig.mp} containing +three figures with charcodes 1, 2, and~3, the proof sheet can be +generated by calling +$$ +\begin{verbatim} +tex mproof fig.? +\end{verbatim} +$$ +The pattern \texttt{fig.?} is automatically expanded to \texttt{fig.1 + fig.2 fig.3} by the shell (but not necessarily in numerically +increasing order) before \TeX\ is run. If there were an output file +\texttt{fig.10}, using patterns \texttt{fig.??} or \texttt{fig.*} to +cover two-digit indices would fail, since those covered the source file +\texttt{fig.mp} as well. To avoid that, output file names have to be +made more significant, e.g., by setting variable \texttt{outputtemplate} +to \verb|%j-%c.mps| (see Section~\ref{Doutputtemplate}). The proof sheet +can then be generated with +$$ +\begin{verbatim} +tex mproof *.mps +\end{verbatim} +$$ + +\paragraph{\texttt{mpsproof.tex}} +\index{mpsproof.tex?\texttt{mpsproof.tex}} + +An alternative to \texttt{mproof.tex} is the script +\texttt{mpsproof.tex}, which is similar, but more powerful. While the +former script only runs with \TeX\ and requires a DVI output driver to +generate PostScript files, \texttt{mpsproof.tex} can as well be run +through pdf\TeX\ to directly generate PDF files. Additionally, it +provides some command-line options. + +With the +\verb|\noheaders|\index{mpsproof.tex?\texttt{mpsproof.tex}!noheaders?\texttt{\textbackslash + noheaders}} option, file names, date stamps, and page numbers are +omitted from the proof sheet. Use it like +$$ +\begin{verbatim}[commandchars=\|\{\}] +tex mpsproof \noheaders |tdescr{MetaPost output files} +\end{verbatim} +$$ + +The +\verb|\bbox|\index{mpsproof.tex?\texttt{mpsproof.tex}!bbox?\texttt{\textbackslash + bbox}} option can be used to generate an output file that has +exactly the same page size as a figure's bounding box (\verb|\bbox| is +actually an alias for the longer +\verb|\encapsulate|\index{mpsproof.tex?\texttt{mpsproof.tex}!encapsulate?\texttt{\textbackslash + encapsulate}}). With this option only one figure can be processed +at a time, e.g., +$$ +\begin{verbatim} +pdftex mpsproof \bbox fig.1 +\end{verbatim} +$$ + +\paragraph{Alternatives} Other alternatives for previewing MetaPost +figures, which are not part of the MetaPost distribution, are the +mptopdf\index{mptopdf} bundle or the Perl script \ttindex{mpstoeps.pl}. +There is also an online compiler and viewer for MetaPost code at +\url{http://tlhiv.org/mppreview/}. + +\subsection{Debugging} +\label{debug} + +\index{debug} + +MetaPost inherits from \MF\index{metafont?\MF} numerous facilities for +interactive debugging, most of which can only be mentioned briefly here. +Further information on error messages, debugging, and generating tracing +information can be found in {\sl The\ \MF book} \cite{kn:c}. + +Suppose your input file says +$$ \hbox{\verb|draw z1--z2;|} $$ +on line 17 without first giving known values to {\tt z1} and {\tt z2}. +Figure~\ref{errmsg} shows what the MetaPost interpreter prints on your +terminal when it finds the error. The actual error message is the line +beginning with ``{\tt !}''; the next six lines give the context that +shows exactly what input was being read when the error was found; and +the ``{\tt ?}'' on last line is a prompt for your response. Since the +error message talks about an undefined $x$~coordinate, this value is +printed on the first line after the ``\verb|>>|''. In this case the +$x$~coordinate of {\tt z1} is just the unknown variable {\tt x1}, so the +interpreter prints the variable name {\tt x1} just as it would if it +were told to\index{show?\texttt{show}} ``{\tt show x1}'' at this point. + +\begin{figure}[htp] +$$\begin{verbatim} +>> x1 +! Undefined x coordinate has been replaced by 0. +<to be read again> + { +--->{ + curl1}..{curl1} +l.17 draw z1-- + z2; +? +\end{verbatim} +$$ +\caption{An example of an error message.} +\label{errmsg} +\end{figure} + +The context listing may seem a little confusing at first, but it really just +gives a few lines of text showing how much of each line has been read so far. +Each line of input is printed on two lines like this: +\begin{eqnarray*} + \descr{descriptor}\ \hbox{Text read so far} \\ + && \hbox{Text yet to be read} +\end{eqnarray*} +The \tdescr{descriptor} identifies the input source. It is either a +line number like ``{\tt l.17}'' for line 17 of the current file; or it +can be a macro name followed by ``{\tt ->}''; or it is a descriptive +phrase in angle brackets. Thus, the meaning of the context listing in +Figure~\ref{errmsg} is that the interpreter has just read line 17 of the +input file up to ``\verb|--|,'' the expansion of the \verb|--| macro has +just started, and the initial ``\verb|{|'' has been reinserted to allow +for user input before scanning this token. + +Among the possible responses to a {\tt ?} prompt are the following: +\begin{description} +\item[x] terminates the run so that you can fix your input file and start over. +\item[h] prints a help message followed by another {\tt ?} prompt. +\item[\tdescr{return}] causes the interpreter to proceed as best it can. +\item[?] prints a listing of the options available, followed by another + {\tt ?} prompt. +\end{description} + +This interactive mode is not only entered when MetaPost finds an error +in the code. It can be explicitly entered by the \ttindex{errmessage} +command. The \ttindex{message}\label{Dmessage} command writes a string +argument to a new line on the terminal. The +\ttindex{errmessage}\label{Derrmessage} command is similar, but the +string argument is preceded by \verb|"! "| and followed by~\verb|"."|. +Additionally, some lines of context are appended as in MetaPost's normal +error messages. If the user now types ``h'', the most recent +\ttindex{errhelp}\label{Derrhelp} string will be shown (unless it was +empty). + +\begin{figure}[htp] +\begin{ctabbing} +$\tt \descr{message command} \rightarrow errhelp \descr{string expression}$\\ +$\tt \qquad \;|\; errmessage \descr{string expression}$\\ +$\tt \qquad \;|\; message \descr{string expression}$ +\end{ctabbing} +\caption{The syntax for message commands} +\label{symsg} +\end{figure} + +Error messages and responses to {\tt show} commands are also written +into the transcript\index{files!transcript} file whose name is obtained +from the name of the main input file by changing ``{\tt .mp}''\index{mp + file?{\tt mp} file}\index{files!mp?{\tt mp}} to ``{\tt + .log}''\index{log file?{\tt log} file}\index{files!log?{\tt + log}}. When the internal variable\index{internal + variables}\index{variables!internal} {\tt + tracingonline}\index{tracingonline?\texttt{tracingonline}} is at its +default value of zero, some {\tt show} commands print their results in +full detail only in the transcript file. + +Only one type of {\tt show}\index{show?\texttt{show}} command has been +discussed so far: {\tt show} followed by a comma-separated list of +expressions prints symbolic representations of the expressions. + +The {\tt showtoken}\index{showtoken?\texttt{showtoken}}\label{Dshtok} +command can be used to show the +parameters and replacement text of a macro. It takes a comma-separated list of +tokens and identifies each one. If the token is a primitive as in +``\verb|showtoken +|'' it is just identified as being itself: +$$ \hbox{\verb|> +=+|} $$ +Applying {\tt showtoken} to a variable or a {\tt vardef} macro yields +$$ \hbox{\tt > } \descr{token}\hbox{\tt =variable} $$ + +To get more information about a variable, use +{\tt showvariable}\index{showvariable?\texttt{showvariable}}\label{Dshvar} +instead of {\tt showtoken}. The +argument to {\tt showvariable} is a comma-separated list of symbolic tokens +and the result is a description of all the variables whose names begin with +one of the listed tokens. This even works for {\tt vardef} macros. For +example, {\tt showvariable z} yields +$$ \hbox{\verb|z@#=macro:->begingroup(x(SUFFIX2),y(SUFFIX2))endgroup|} $$ + +There is also a {\tt +showdependencies}\index{showdependencies?\texttt{showdependencies}}\label{Dshdep} +command that takes no arguments and prints a list of all {\em dependent} +variables and how the linear equations given so far make them depend on +other variables. Thus after +$$ \hbox{\tt z2-z1=(5,10); z1+z2=(a,b);} $$ +{\tt showdependencies} prints what is shown in Figure~\ref{shdep}. This could +be useful in answering a question like ``What does it mean +`{\tt !\ Undefined x coordinate}?' I thought the equations given so far would +determine {\tt x1}.'' + +\begin{figure}[htp] +$$\begin{verbatim} +x2=0.5a+2.5 +y2=0.5b+5 +x1=0.5a-2.5 +y1=0.5b-5 +\end{verbatim} +$$ +\caption{The result of {\tt z2-z1=(5,10); z1+z2=(a,b); showdependencies;}} +\label{shdep} +\end{figure} + +When all else fails, the predefined macro {\tt +tracingall}\index{tracingall?\texttt{tracingall}}\label{Dtall} causes +the interpreter to print a detailed listing of everything it is doing. +Since the tracing information is often quite voluminous, it may be +better to use the {\tt +loggingall}\index{loggingall?\texttt{loggingall}}\label{Dlogall} macro +that produces the same information but only writes it in the +transcript\index{files!transcript} file. There is also a {\tt +tracingnone}\index{tracingnone?\texttt{tracingnone}}\label{Dtnone} macro +that turns off all the tracing output. + +Tracing output is controlled by the set of internal +variables\index{internal variables}\index{variables!internal} summarized +below. When any one of these variables is given a positive value, the +corresponding form of tracing is turned on. Here is the set of tracing +variables and what happens when each of them is positive: +\begin{description} +\item[{\tt tracingcapsules}]\index{tracingcapsules?\texttt{tracingcapsules}}\label{Dtcapsules}% +shows the values of temporary quantities (capsules) when they become known. +% +\item[{\tt tracingchoices}]\index{tracingchoices?\texttt{tracingchoices}}\label{Dtchoices}% +shows the B\'ezier control\index{control points} points of each new path +when they are chosen. % +\item[{\tt tracingcommands}]\index{tracingcommands?\texttt{tracingcommands}}\label{Dtcommands}% +shows the commands before they are performed. A setting ${}>1$ also shows +{\tt if}\index{if?\texttt{if}} tests and loops before they are expanded; +a setting ${}>2$ shows algebraic operations before they are performed. +% +\item[{\tt tracingequations}]\index{tracingequations?\texttt{tracingequations}}\label{Dtequations}% +shows each variable when it becomes known. +% +\item[{\tt tracinglostchars}]\index{tracinglostchars?\texttt{tracinglostchars}}\label{Dtlostchars}% +warns about characters omitted from a picture because they are not in the font +being used to typeset labels. +% +\item[{\tt tracingmacros}]\index{tracingmacros?\texttt{tracingmacros}}\label{Dtmacros}% +shows macros before they are expanded. +% +\item[{\tt tracingoutput}]\index{tracingoutput?\texttt{tracingoutput}}\label{Dtoutput}% +shows pictures as they are being shipped out as PostScript files. +% +\item[{\tt tracingrestores}]\index{tracingrestores?\texttt{tracingrestores}}\label{Dtrestores}% +shows symbols and internal variables as they are being restored at the end +of a group. +% +\item[{\tt tracingspecs}]\index{tracingspecs?\texttt{tracingspecs}}\label{Dtspecs}% +shows the outlines generated when drawing with a +polygonal pen\index{pens!polygonal}. +% +\item[{\tt tracingstats}]\index{tracingstats?\texttt{tracingstats}}\label{Dtstats} +shows in the transcript file at the end of the job how many of the +MetaPost interpreter's limited resources were used. +\end{description} + +\subsection{Importing MetaPost Graphics into External Applications} +\label{mpimport} + +MetaPost is very well suited for creating graphics that are to be +included into third-party applications, such as text documents, +presentations or web pages, because MetaPost outputs graphics in vector +formats, which can be scaled without quality degradation. However, +practice shows, that vector graphics, too, are best created with a rough +target size already in mind. Scaling a vector graphic calls for +non-proportional scaling of certain technical parameters, such as line +width, arrow size or fonts. Otherwise, with growing scale factors +scalable graphics tend to change their visual character. Additionally, +during import into a main document, they'll likely fail to match, e.g., +stroke width of the document. To circumvent this, it is advisable to +apply only small post-processing scale factors to vector graphics. The +following sections briefly discuss how to import MetaPost graphics into +documents with selected applications. + +\subsubsection{\TeX\ and Friends} +\label{teximport} +\index{TeX?\TeX!and friends} + +MetaPost graphics in the PostScript\index{PostScript} format can be +easily integrated into documents prepared with \TeX\ and friends. +MetaPost's PostScript output is a low-featured dialect of the Postscript +language, called \emph{purified EPS}\index{EPS!purified}, which can be +converted into the Portable Document Format (PDF\index{PDF}) language +on-the-fly. For that reason, external MetaPost graphics can be used on +both routes: a) using the traditional \TeX\ engine together with an +external PostScript output driver and b) using newer \TeX\ engines, like +pdf\TeX\ or its successor Lua\TeX, which contain a built-in PDF output +driver. Lua\TeX\ can additionally process embedded MetaPost code +natively, falling back to the built-in \emph{mplib} library. + +Figure~\ref{fig:teximport} shows the process of including an external +MetaPost graphic into a \TeX\ document using the PostScript route. In +the \TeX\ source a ``magic macro'' provided by the format or an external +package is used for including a graphic file. During the typesetting +stage, the macro only reads bounding box information off the PostScript +file and reserves the required space on the page via an empty box. The +file reference is passed-on to the output driver and only then, finally, +the file is embedded into the document. The freely available program +\ttindex{dvips} is used as an output driver in this +example.\footnote{The C source for \ttt{dvips} comes with the web2c + \TeX\ distribution. Similar programs are available from other + sources.} The next paragraphs give more detailed information on some +popular combinations of \TeX\ formats and engines. + +\begin{figure} +$$ \includegraphics{mpman-charts-1.mps} $$ +\caption{A diagram of the processing for a \TeX\ document embedding + MetaPost figures} +\label{fig:teximport} +\end{figure} + +\paragraph{Plain \TeX\ Format} +\label{plaintexformat} +\index{TeX?\TeX!format, plain!importing MetaPost files} + +For users of the Plain \TeX\ format and the traditional \TeX\ +engine\index{TeX?\TeX!engine} with Device Independend output +(DVI\index{dvi file?{\tt dvi} file}) the +\ttt{epsf}\index{epsf.tex?\texttt{epsf.tex}} package provides the +``magic macro'' +$$ \verb|\epsfbox{|\descr{filename}\verb|}|% +\index{epsfbox?\texttt{\string\epsfbox}} $$ +for embedding graphics, e.g., \verb|\epsfbox{fig.1}|. + +Users of the pdf\TeX\ engine\index{pdfTeX?pdf\TeX!engine} should refer +to the standalone macros of the mptopdf\index{mptopdf} bundle, which can +be found at \url{http://context.aanhet.net/mptopdf.htm}. + +With the Lua\TeX\ engine\index{LuaTeX?Lua\TeX!engine}, embedding +external graphics works the same as with pdf\TeX. Additionally, +Lua\TeX\ users can inline MetaPost code directly into Plain \TeX\ +documents. Lua\TeX\ is able to process such MetaPost code snippets, +falling back to the built-in \emph{mplib}\index{mplib?\emph{mplib}} +library. Note, \emph{mplib} doesn't support +\verb|verbatimtex|\slash\verb|btex| \ldots\ \verb|etex| constructs, +currently. Here is an example of a MetaPost graphic inlined into a +Plain \TeX\ document. For more information, please refer to the +Lua\TeX~\cite[chap.~4.8]{luatex:manual} and +\ttindex{luamplib}~\cite{hagen:luamplib} documentation. + +$$\begin{verbatim} +\input luamplib.sty +\mplibcode +beginfig(1); + ... +endfig; +\endmplibcode +\bye +\end{verbatim} +$$ + +\paragraph{\LaTeX\ Format} +\label{latexformat} +\index{LaTeX?\LaTeX!format!importing MetaPost files} +\index{TeX?\TeX!engine} +\index{pdfTeX?pdf\TeX!engine} + +For users of the \LaTeX\ format and the traditional \TeX\ engine with +Device Independent output (DVI\index{dvi file?{\tt dvi} file}) the +well-known \ttindex{graphics} (or \ttindex{graphicx}) package aids in +external graphics inclusion. The package supports different engines, +guessing the correct output driver automatically, and can handle several +graphic formats. The ``magic macro'' is +$$ \verb|\includegraphics{|\descr{filename}\verb|}|% +\index{includegraphics?\texttt{\string\includegraphics}} $$ + +In DVI output driver mode the \ttt{graphics} package assumes all files +with an unknown file extension, such as \texttt{.1} etc., to be in the +EPS\index{EPS} format. It therefore handles MetaPost files with a +numeric default file extension correctly (see~\cite{reckdahl:epslatex} +for more information). + +When using the pdf\TeX\ engine with a built-in PDF output driver, the +situation is a bit different. Only files with file extension +\texttt{.mps}\index{mps file?{\tt mps} file}\index{files!mps?{\tt mps}} +are recognized as purified EPS\index{EPS!purified} and can be converted +to PDF\index{PDF} on-the-fly. The recommended procedure for embedding +MetaPost graphics into \LaTeX\ documents compiled with pdf\TeX\ is +therefore to change MetaPost's output file name extension via +\verb|outputtemplate|\index{outputtemplate?\texttt{outputtemplate}} (see +p.~\pageref{Doutputtemplate}). In the \LaTeX\ document include the +graphic files with full name, e.g., +$$\begin{verbatim} +\includegraphics{fig-1.mps} +\end{verbatim} +$$ + +Note, the latter approach works with the \ttindex{dvips} driver, too. +Even though, again, this time \ttt{.mps} is an unknown file extension, +triggering EPS file handling in a fall-back procedure. This property of +the \ttt{graphics} package, which comes in handy for MetaPost files, is +the reason many MetaPost source files start with the line +$$\begin{verbatim} +outputtemplate := "%j-%c.mps"; +\end{verbatim} +$$ + +With the Lua\TeX\ engine\index{LuaTeX?Lua\TeX!engine}, embedding +external graphics works the same as with pdf\TeX. Additionally, +Lua\TeX\ users can inline MetaPost code directly into La\TeX\ documents. +Lua\TeX\ is able to process such MetaPost code snippets, falling back to +the built-in \emph{mplib}\index{mplib?\emph{mplib}} library. Note, +\emph{mplib} doesn't support \verb|verbatimtex|\slash\verb|btex| \ldots\ +\verb|etex| constructs, currently. Here is an example of a MetaPost +graphic inlined into a \LaTeX\ document. For more information, please +refer to the Lua\TeX~\cite[chap.~4.8]{luatex:manual} and +\ttindex{luamplib}~\cite{hagen:luamplib} documentation. +$$\begin{verbatim} +\documentclass{article} +\usepackage{luamplib} +\begin{document} +\begin{mplibcode} +beginfig(1); + ... +endfig; +\end{mplibcode} +\end{document} +\end{verbatim} +$$ + +\paragraph{Con\TeX t Format} +\label{contextformat} +\index{ConTeXt?Con\TeX t!format!importing MetaPost files} + +In Con\TeX t\index{ConTeXt?Con\TeX t} graphics support is integrated in +the kernel, covering advanced features like shading, transparency, color +spaces or image inclusion. The ``magic macro'' for embedding external +graphics is +$$ \verb|\externalfigure[|\descr{filename}\verb|]|% +\index{externalfigure?\texttt{\string\externalfigure}} $$ +% +The macro can handle numbered files as well as files with the \ttt{mps} +suffix. + +Alternatively, Con\TeX t users can inline MetaPost code in the document +source, which allows for more natural interfacing with document +properties, font support, and automatic processing~\cite{hagen:metafun}. +Here is an example of a MetaPost graphic inlined into a Con\TeX t +document. +$$\begin{verbatim}[commandchars=|\[\]] +\starttext +\startuseMPgraphic{|tdescr[name]} + ... +\stopuseMPgraphic +\useMPgraphic{|tdescr[name]} +\stoptext +\end{verbatim} +$$ + +Con\TeX t MkIV, being based on the Lua\TeX\ engine, provides a much +tighter integration of MetaPost than older versions, since it can +fall-back to the built-in \emph{mplib}\index{mplib?\emph{mplib}} +library. + +\subsubsection{Troff} +\label{troffimport} +\index{troff!importing MetaPost files} + +It is also possible to include MetaPost output in a GNU +troff\index{troff} document. The procedure is similar to +Figure~\ref{fig:teximport}: the \ttindex{grops} output processor +includes PostScript files when they are requested via troff's +\ttt{\string\X}\index{X?\texttt{\string\X}} command. The +\ttt{-mpspic}\index{mpspic?\texttt{-mpspic}} macro package provides a +command \verb|.PSPIC|\index{PSPIC?\texttt{.PSPIC}}, which does just that +when including an encapsulated PostScript file in the source code. For +instance, the troff command +$$ \hbox{\verb|.PSPIC fig.1|} $$ +includes \ttt{fig.1}, using the natural height and width of the +image as given in the file's bounding box. + +\subsubsection{Web Applications} +\label{webimport} + +An SVG\index{svg file?{\tt svg} file}\index{files!svg?{\tt svg}} file +\texttt{fig.svg} can be easily embedded into +HTML\index{HTML}\index{files!HTML} documents with the following code +snippet: +$$\begin{verbatim} +<p> + <object data="fig.svg" type="image/svg+xml" width="300" height="200"> + </object> +</p> +\end{verbatim} +\index{object tag?\texttt{object} tag|see{HTML, tags, \texttt{object}}} +\index{HTML!tags!object?\texttt{object}} +$$ +The code is similar for PNG\index{png file?{\tt png} + file}\index{files!png?{\tt png}} files: +$$\begin{verbatim} +<p> + <img src="fig.png" alt="A picture."> +</p> +\end{verbatim} +\index{img tag?\texttt{img} tag|see{HTML, tags, \texttt{img}}} +\index{HTML!tags!img?\texttt{img}} +$$ +The \texttt{width} and \texttt{height} attributes used above allow for +scaling a graphic to an arbitrary size. More information about HTML +tags and attributes can be found in an HTML reference. + +SVG and PNG files can also be imported by various interactive graphics +editing programs, for example GIMP\index{GIMP} or +Inkscape\index{Inkscape}. See Section~\ref{Dprologues} for information +on font handling in SVG graphics. + + +\section*{Acknowledgement} + +I would like to thank Don Knuth for making this work possible by +developing \MF\ and placing it in the public domain. I am also indebted +to him for helpful suggestions, particularly with regard to the +treatment of included \TeX\ material. + + +\appendix +\include{mpman-app-numbersystems} +\include{mpman-app-refman} +\include{mpman-app-legacy} + + +\bibliographystyle{plain} +\bibliography{mpman} + + +\printindex + + +\end{document} + +% Copyright 1990 - 1995 by AT&T Bell Laboratories. +% Updated 2006 by Taco Hoekwater, Karl Berry, and others. + +% Permission to use, copy, modify, and distribute this software +% and its documentation for any purpose and without fee is hereby +% granted, provided that the above copyright notice appear in all +% copies and that both that the copyright notice and this +% permission notice and warranty disclaimer appear in supporting +% documentation, and that the names of AT&T Bell Laboratories or +% any of its entities not be used in advertising or publicity +% pertaining to distribution of the software without specific, +% written prior permission. + +% AT&T disclaims all warranties with regard to this software, +% including all implied warranties of merchantability and fitness. +% In no event shall AT&T be liable for any special, indirect or +% consequential damages or any damages whatsoever resulting from +% loss of use, data or profits, whether in an action of contract, +% negligence or other tortious action, arising out of or in +% connection with the use or performance of this software. + +% In addition, John Hobby, the original author of MetaPost and this +% manual, makes the following requests: +% - I request that it remain clear that I am the author of +% "A User's Manual for MetaPost" and "Drawing Graphs with MetaPost". +% - I request to be consulted before significant changes are made. + +%%% Local Variables: +%%% mode: latex +%%% TeX-PDF-mode: t +%%% TeX-master: t +%%% End: |