summaryrefslogtreecommitdiff
path: root/graphics/pgf/base/doc/text-en/pgfmanual-en-base-arrows.tex
diff options
context:
space:
mode:
authorNorbert Preining <norbert@preining.info>2023-01-16 03:03:27 +0000
committerNorbert Preining <norbert@preining.info>2023-01-16 03:03:27 +0000
commit6f9e1680085e7bb4d258f6f8116369d122e196e1 (patch)
tree9ac0ecb239240d1d672b188f29c1479de215074b /graphics/pgf/base/doc/text-en/pgfmanual-en-base-arrows.tex
parentb8345f39630408bb198e7636381ce4240154ca9b (diff)
CTAN sync 202301160303
Diffstat (limited to 'graphics/pgf/base/doc/text-en/pgfmanual-en-base-arrows.tex')
-rw-r--r--graphics/pgf/base/doc/text-en/pgfmanual-en-base-arrows.tex962
1 files changed, 0 insertions, 962 deletions
diff --git a/graphics/pgf/base/doc/text-en/pgfmanual-en-base-arrows.tex b/graphics/pgf/base/doc/text-en/pgfmanual-en-base-arrows.tex
deleted file mode 100644
index 5d81abf79d..0000000000
--- a/graphics/pgf/base/doc/text-en/pgfmanual-en-base-arrows.tex
+++ /dev/null
@@ -1,962 +0,0 @@
-% Copyright 2019 by Till Tantau
-%
-% This file may be distributed and/or modified
-%
-% 1. under the LaTeX Project Public License and/or
-% 2. under the GNU Free Documentation License.
-%
-% See the file doc/generic/pgf/licenses/LICENSE for more details.
-
-
-\section{Defining New Arrow Tip Kinds}
-\label{section-arrows}
-
-\subsection{Overview}
-
-In present section we have a look at how you can define new arrow tips for use
-in \pgfname. The low-level commands for selecting which arrow tips are to be
-used have already been described in Section~\ref{section-tips}, the general
-syntax rules for using arrows are detailed in
-Section~\ref{section-tikz-arrows}. Although Section~\ref{section-tikz-arrows}
-describes the use of arrows in \tikzname, in reality, \tikzname\ itself does
-not actually do anything about arrow tips; all of the functionality is
-implemented on the \pgfname\ level in the commands described in
-Section~\ref{section-tikz-arrows}. Indeed, even the |/.tip| key handler
-described in Section~\ref{section-tikz-arrows} is actually implemented on the
-\pgfname\ layer.
-
-What has \emph{not} yet been covered is how you can actually define a complete
-new arrow tip. In \pgfname, arrows are ``meta-arrows'' in the same way that
-fonts in \TeX\ are ``meta-fonts''. When a meta-arrow is resized, it is not
-simply scaled, but a possibly complicated transformation is applied to the
-size.
-
-A meta-font is not one particular font at a specific size with a specific
-stroke width (and with a large number of other parameters being fixed). Rather,
-it is a ``blueprint'' (actually, more like a program) for generating such a
-font at a particular size and width. This allows the designer of a meta-font to
-make sure that, say, the font is somewhat thicker and wider at very small
-sizes. To appreciate the difference: Compare the following texts: ``Berlin''
-and ``\tikz{\node [scale=2,inner sep=0pt,outer sep=0pt]{\tiny Berlin};}''. The
-first is a ``normal'' text, the second is the tiny version scaled by a factor
-of two. Obviously, the first look better. Now, compare ``\tikz{\node
-[scale=.5,inner sep=0pt,outer sep=0pt]{Berlin};}'' and ``{\tiny Berlin}''. This
-time, the normal text was scaled down, while the second text is a ``normal''
-tiny text. The second text is easier to read.
-
-\pgfname's meta-arrows work in a similar fashion: The shape of an arrow tip can
-vary according to a great number of parameters, the line width of the arrow tip
-being one of them. Thus, an arrow tip drawn at a line width of 5pt will
-typically \emph{not} be five times as large as an arrow tip of line width 1pt.
-Instead, the size of the arrow will get bigger only slowly as the line width
-increases.
-
-To appreciate the difference, here are the |Latex| and
-|Classical TikZ Rightarrow| arrows, as drawn by \pgfname\ at four different
-sizes:
-
-\medskip
-\begin{tikzpicture}[1/.tip=Latex, 2/.tip=Classical TikZ Rightarrow]
- \draw[-1, line width=0.1pt] (0pt,0ex) -- +(3,0) node[thin,right] {line width is 0.1pt};
- \draw[-1, line width=0.4pt] (0pt,-2em) -- +(3,0) node[thin,right] {line width is 0.4pt};
- \draw[-1, line width=1.2pt] (0pt,-4em) -- +(3,0) node[thin,right] {line width is 1.2pt};
- \draw[-1, line width=5pt] (0pt,-6em) -- +(3,0) node[thin,right] {line width is 5pt};
-
- \draw[-2, line width=0.1pt] (6cm,0ex) -- +(3,0) node[thin,right] {line width is 0.1pt};
- \draw[-2, line width=0.4pt] (6cm,-2em) -- +(3,0) node[thin,right] {line width is 0.4pt};
- \draw[-2, line width=1.2pt] (6cm,-4em) -- +(3,0) node[thin,right] {line width is 1.2pt};
- \draw[-2, line width=5pt] (6cm,-6em) -- +(3,0) node[thin,right] {line width is 5pt};
-\end{tikzpicture}
-
-\medskip
-Here, by comparison, are the same arrows when they are simply ``resized'':
-
-\medskip
-\begin{tikzpicture}[1/.tip=Latex, 2/.tip=Classical TikZ Rightarrow]
- \draw[-{1[length=1pt]}, line width=0.1pt] (0pt,0ex) -- +(3,0) node[thin,right] {line width is 0.1pt};
- \draw[-{1[length=4pt]}, line width=0.4pt] (0pt,-2em) -- +(3,0) node[thin,right] {line width is 0.4pt};
- \draw[-{1[length=12pt]}, line width=1.2pt] (0pt,-4em) -- +(3,0) node[thin,right] {line width is 1.2pt};
- \draw[-{1[length=32pt]}, line width=5pt] (0pt,-6em) -- +(3,0) node[thin,right] {line width is 5pt};
-
- \draw[-{2[length=0.455pt]}, line width=0.1pt] (6cm,0ex) -- +(3,0) node[thin,right] {line width is 0.1pt};
- \draw[-{2[length=1.82pt]}, line width=0.4pt] (6cm,-2em) -- +(3,0) node[thin,right] {line width is 0.4pt};
- \draw[-{2[length=5.46pt]}, line width=1.2pt] (6cm,-4em) -- +(3,0) node[thin,right] {line width is 1.2pt};
- \draw[-{2[length=14.56pt]}, line width=5pt] (6cm,-6em) -- +(3,0) node[thin,right] {line width is 5pt};
-\end{tikzpicture}
-
-\bigskip
-As can be seen, simple scaling produces arrow tips that are way too large at
-larger sizes and way too small at smaller sizes.
-
-In addition to the line width, other options may also influence the appearance
-of an arrow tip. In particular, the width of the inner line (the line used to
-create the effect of a double line) influences arrow tips as well as other
-options that are specific to the arrow tip.
-
-
-\subsection{Terminology}
-\label{section-arrow-terminology}
-
-Before we have a look at the exact commands used for defining arrow tips, we
-need to fix some terminology. Consider the following drawing of an arrow tip
-where the arrow tip is drawn transparently so that we can see what is
-``happening behind it'':
-%
-\begin{tikzpicture}
- \draw [red!50, ,line width=1cm] (0,0) -- (4,0);
- \path [tips, opacity=.25,line width=1cm, -{Stealth[black,line width=0pt,length=4cm, width=4cm, inset=1cm]}] (0,0) -- (6,0);
-
- \draw [->,thick] (1,0) -- (8,0) node [right] {$x$-axis};
- \draw [->,thick] (5,-2.25) -- (5,2.25) node [above] {$y$-axis};
-
- \foreach \i in {-3,-2,-1,1,2} \draw (\i+5,-1mm) -- (\i+5,1mm) node [above] {\small$\i$};
- \foreach \i in {-2,-1,1,2} \draw (49mm,\i) -- (51mm,\i) node [right] {\small$\i$};;
-\end{tikzpicture}
-
-I have also added a coordinate system. The code for drawing an arrow tip always
-draws it in the way shown above: Pointing right along the $x$-axis.
-
-We will use the following terminology:
-%
-\begin{itemize}
- \item The point where tip of the arrow ends is called the \emph{tip end}.
- It is at $(1,0)$ in our example and we always assume it to lie on the
- $x$-axis, so we just treat it as a distance, 1 in this case. This is
- the position where the original path was supposed to end (so if the
- arrow tip had not been added to the red path, it would have ended
- here).
- \item The \emph{back end} of the arrow is where a vertical line just to the
- left of the arrow intersects the $x$-axis. In our case, this is the
- point $(-3,0)$ and again we treat it as a distance, $-3$ in this case.
- \item The \emph{line end} is the position where the path now ends. This
- should be a position inside the arrow head that gets ``covered'' by the
- path. Note that a path may have a round or a rect head and should still
- be covered. Clearly, necessary shortening of the path will be the
- difference between the tip end and the line end.
- \item The \emph{visual back end} is the position where the path and the the
- arrow head ``meet last'' on the path. In our case, because of the
- inset, the visual back end is not the same as the back end: The arrow
- ends ``visually'' at $(-2,0)$. The difference between the back end and
- the visual back end is important when the arrow tip is flexed, see
- Section~\ref{section-arrow-flex} for an explanation of flexing.
- \item There is also a \emph{visual tip end}, the counterpart of the visual
- back end for the front. In our case, the visual tip end and the tip end
- obviously coincide, but if we were to reverse the arrow tip, the visual
- tip end would be different from the tip end (while the visual back end
- would then coincide with the new back end).
- \item There are four points that make up the \emph{convex hull} of the
- arrow tip: $(1,0)$, $(-3,2)$, and $(-3,-2)$.
-
- Normally, \pgfname\ automatically keeps track of a bounding box of
- everything you draw. However, since arrow tips are drawn so often,
- \pgfname\ caches the code needing for drawing arrow tips internally and
- because of this cache it cannot determine the size of the arrow tip
- just based on the drawing commands used for drawing the tip. Instead, a
- convex hull of the arrow tip must be explicitly provided in the
- definition.
-\end{itemize}
-
-When you design a new arrow tip, all of the above parameters must be defined.
-
-
-\subsection{Caching and Rendering of Arrows}
-
-As a last preparation for the description of the commands for declaring arrows,
-it is important to understand the exact process by which \pgfname\ draws
-arrows.
-%
-\begin{enumerate}
- \item First, you have to define an arrow tip kind using
- |\pgfdeclarearrow{name=foo,...|. This will tell \pgfname\ that |foo| is %}
- now the name of an arrow tip. In particular, the parser for arrow tip
- specifications will now treat |foo| as the name of an arrow tip and
- will not try to consider |f|, |o|, and |o| as the names of single-char
- shorthands.
-
- Other than storing the definitions in the declaration internally, this
- command has little other effect. In particular, no drawing or other
- processing takes place.
- \item Now assume that at some point the arrow tip |foo| is actually used.
- In this case, certain options may have been set, for instance the user
- may have requested the arrow tip |foo[length=5pt,open]|. What happens
- next depends on whether it is the first time the arrow tip |foo| is
- used with \emph{these exact options} or not.
- \item Assume that is the first time |foo| is requested at a length of 5pt
- and in an ``open'' version. \pgfname\ now retrieves the definition of
- the arrow tip kind that it stored in the first step and executes the
- so-called \emph{setup} code. When this code is executed, all the
- options will be in force (for instance, |\pgfarrowlength| will equal
- |5pt| in our case). The job of the setup code is two-fold: First, it
- needs to compute all of the parameters listed in
- Section~\ref{section-arrow-terminology}, that is, it has to compute
- where the tip end will lie in the arrow tip's coordinate system
- \emph{at the particular size of 5pt}, where the back end will be, where
- the convex hull points lie, and so on. Second, the setup code should
- precompute values that will be important for constructing the path of
- the arrow. In our example, there is little to do in this regard, but
- for more complicated arrows, all time-consuming preparations are done
- now.
-
- It is \emph{not} the job of the setup to actually draw the arrow tip,
- only to ``prepare'' this as much as possible.
-
- The setup code will always be executed only once for each arrow tip
- kind for a given set of options. Thus, when a user uses
- |foo[length=5pt,open]| once more later anywhere in the document, the
- setup code will not be executed again.
- \item The next thing that happens is that we have a look at the
- \emph{drawing code} stored in the |code| field of the arrow. In our
- example, the drawing code would consist of creating a filled path with
- four straight segments.
-
- In most cases, what happens now is that the drawing code is executed in
- a special sandbox in which the low-level driver commands that do the
- actual drawing are intercepted and stored away in a so-called
- \emph{cache}. Once such a cache has been created, its contents will be
- reused whenever |foo[length=5pt,open]| is requested by a user and just
- like the setup code, the drawing code will not be executed again.
-
- There are, however, two cases in which the drawing code gets executed
- each time the arrow is used: First, an arrow tip kind can specify that
- this should always happen by saying |cachable=false| in its definition.
- This is necessary if the drawing code contains low-level drawing
- commands that cannot be intercepted such as a use of |\pgftext| for
- arrow tips that ``contain text''. Second, when the |bend| option is
- used, the same arrow tip will look different each time it is used,
- namely in dependence on the exact curvature of the path to which it is
- added.
-
- Because the drawing code may be executed several times, while the setup
- code may not, we must find a way to ``communicate'' the values computed
- by the setup code to the drawing code. This is done by explicitly
- calling |\pgfarrowssave| inside the setup code. Whatever is ``saved''
- in this way is restored each time before the drawing code is executed.
-\end{enumerate}
-
-As can be seen, the process is a bit involved, but it leads to a reasonably
-fast arrow tip management.
-
-
-\subsection{Declaring an Arrow Tip Kind}
-
-\begin{command}{\pgfdeclarearrow\marg{config}}
- This command is both used to define a new arrow tip kind and to to declare
- a so-called shorthand. We have a look at the case that a complete new arrow
- tip kind is created and then have a look how the command can be used to
- create shorthands.
-
-
- \medskip
- \noindent\textbf{Defining a Complete New Arrow Tip Kind.}
- The \meta{config} is a key--value list in which different keys are used to
- setup the to-be defined arrow. The following keys can be given:
- %
- \begin{itemize}
- \item \declare{|name|}|=|\meta{name} or |name=|\meta{start
- name}|-|\meta{end name}
-
- This defines the name of the arrow tip. It is legal to define an
- arrow tip a second time, in this case the previous definition will
- be overwritten in the current \TeX\ scope. It is customary to use a
- name with an uppercase first letter for a ``complete'' arrow tip
- kind. Short names and lower case names should be used for
- shorthands that change their meaning inside a document, while arrow
- tips with uppercase first letters should not be redefined.
-
- If the name contains a hyphen, the second syntax is assumed and
- everything before the hyphen will be the name used in start arrow
- specifications, while the text after the hyphen is the name used in
- end specifications.
- \item \declare{|parameters|}|=|\marg{list of macros}
-
- As explained earlier, an arrow tip typically needs to be redrawn
- each time an option like |length| or |inset| is changed. However,
- for some arrow tips, the |inset| has no influence, while for other
- it is important whether the arrow is reversed or not. (How keys
- like |length| actually set \TeX\ dimensions like |\pgfarrowlength|
- is explained in Section~\ref{section-arrow-options}.)
-
- The job of the |parameters| key is to specify which dependencies
- the arrow tip has. Everything that will influence any of the
- parameters computed in the setup code or used in the drawing code
- should be listed here.
-
- The \meta{list of macros} will be used inside a
- |\csname|-|\endcsname| pair and should expand to the current values
- of the relevant parameters have. For example, if the arrow tip
- depends on the current value of |\pgfarrowlength| and
- |\pgfarrowwidth| only, then \meta{list of macros} should be set to
- |\the\pgfarrowlength,\the\pgfarrowwidth|. (Actually, the comma is
- optional, the \meta{list of macros} does not really have to be a
- list, just something that can be expanded unambiguously.)
-
- Note that the line width (|\pgflinewidth|) and the inner line width
- (|\pgfinnerlinewidth|) are always parameters and need not be
- specified in the |parameters|.
-
- It is important to get this parameter right. Otherwise, arrow tips
- may look wrong because \pgfname\ thinks that it can reuse some code
- when, in reality, this code actually depends on a parameter not
- listed here.
- \item \declare{|setup code|}|=|\marg{code}
-
- When an arrow tip is used, the value stored in |parameters| is
- expanded and it is tested whether the result was encountered
- before. If not, the \meta{code} gets executed (only this once). The
- code can now do arbitrarily complicated computations the prepare
- the later drawing of the arrow tip. Also the \meta{code} must
- specify the different tip and back ends and the convex hull points.
- This is done by calling the following macros inside the
- \meta{code}:
- %
- \begin{command}{\pgfarrowssettipend\marg{dimension}}
- When this command is called inside the setup code of an arrow
- tip, it specifies that the tip of the drawn arrow will end
- exactly at \meta{dimension}. For example, for our earlier
- example of the large arrow tip, where the tip end was at 1cm,
- we would call
- %
-\begin{codeexample}[code only]
-\pgfarrowssettipend{1cm}
-\end{codeexample}
- %
- Note that for efficiency reasons, the \meta{dimension} is not
- passed through |\pgfmathsetlength|; rather what happens is that
- |\pgf@x=|\meta{dimension} gets executed. In particular, you can
- pack further computations into the \meta{dimension} by simply
- starting it with a number and then appending some code that
- modifies |\pgf@x|. Here is an example where instead of 1cm we
- use $1\mathrm{cm} - \frac12\mathrm{linewidth}$ as the tip end:
- %
-\begin{codeexample}[code only]
-\pgfarrowssettipend{1cm\advance\pgf@x by-.5\pgflinewidth}
-\end{codeexample}
- %
- If the command is not called at all inside the setup code, the
- tip end is set to |0pt|.
- \end{command}
-
- \begin{command}{\pgfarrowssetbackend\marg{dimension}}
- Works like the command for the tip end, only it sets the back
- end. In our example we would call
- %
-\begin{codeexample}[code only]
-\pgfarrowssettipend{-3cm}
-\end{codeexample}
- %
- Defaults to |0pt|.
- \end{command}
-
- \begin{command}{\pgfarrowssetlineend\marg{dimension}}
- Sets the line end, so in the example we have
- |\pgfarrowssettipend{-1cm}|. Default to |0pt|.
- \end{command}
-
- \begin{command}{\pgfarrowssetvisualbackend\marg{dimension}}
- Sets the visual back end, |\pgfarrowssetvisualbackend{-2cm}| in
- our example. Default to the value of the normal back end.
- \end{command}
-
- \begin{command}{\pgfarrowssetvisualtipend\marg{dimension}}
- Sets the visual tip end. Default to the value of the normal tip
- end and, thus, we need not set it in our example.
- \end{command}
-
- \begin{command}{\pgfarrowshullpoint\marg{x dimension}\marg{y dimension}}
- Adds a point to the convex hull of the arrow tip. As for the
- previous commands, no math parsing is done; instead \pgfname\
- says |\pgf@x=|\meta{x dimension} and then |\pgf@y=|\meta{y
- dimension}. Thus, both ``dimensions'' can contain code for
- advancing and thus modifying |\pgf@x| and |\pgf@y|.
-
- In our example we would write
- %
-\begin{codeexample}[code only]
-\pgfarrowshullpoint{1cm}{0pt}
-\pgfarrowshullpoint{-3cm}{2cm}
-\pgfarrowshullpoint{-3cm}{-2cm}
-\end{codeexample}
- \end{command}
-
- \begin{command}{\pgfarrowsupperhullpoint\marg{x dimension}\marg{y dimension}}
- This command works like the previous command, only it normally
- adds \emph{two} points to the convex hull: First, the point
- $(\meta{x dimension},\meta{y dimension})$ and, secondly, the
- point $(\meta{x dimension},-\meta{y dimension})$. However, the
- second point is only added if the arrow is not a harpoon.
-
- Thus, in our example we could simplify the convex hull to
- %
-\begin{codeexample}[code only]
-\pgfarrowshullpoint{1cm}{0pt}
-\pgfarrowsupperhullpoint{-3cm}{2cm}
-\end{codeexample}
- %
- If the \meta{y dimension} is zero or less, only one point,
- namely $(\meta{x dimension},\meta{y dimension})$, is added to
- the hull. Thus, we could also have used the upper convex hull
- command in the first of the two of the above commands.
- \end{command}
-
- \begin{command}{\pgfarrowssave\marg{macro}}
- As explained earlier, the setup code needs to ``communicate''
- with the drawing code via ``saved values''. This command get
- the name of a macro and will store the value this macro had
- internally. Then, each time drawing code is executed, the value
- of this macro will be restored.
- \end{command}
-
- \begin{command}{\pgfarrowssavethe\marg{register}}
- Works like |\pgfarrowssave|, only the parameter must be a
- register and |\the|\meta{register} will be saved. Typically,
- you will write something like
- %
-\begin{codeexample}[code only]
-\pgfarrowssavethe{\pgfarrowlength}
-\pgfarrowssavethe{\pgfarrowwidth}
-\end{codeexample}
- %
- To ensure that inside the drawing code the the dimension
- registers |\pgfarrowlength| and |\pgfarrowwidth| are setup with
- the values they had during the setup.
- \end{command}
- \item \declare{|drawing code|}|=|\marg{code}
-
- This code will be executed at least once for each setting of the
- parameters when the time arrow tip is actually drawn. Usually, this
- one execution will be all and the low-level commands generated
- inside the \meta{code} will we stored in a special cache; but in
- some cases the \meta{code} gets executed each time the arrow tip is
- used, so do not assume anything about it. Inside the \meta{code},
- you have access to all values that were saved in the setup code as
- well as to the line width.
-
- The \meta{code} should draw the arrow tip ``going right along the
- $x$-axis''. \pgfname\ will take care of setting up a canvas
- transformation beforehand to a rotation such that when the drawing
- is rendered, the arrow tip that is actually drawn points in the
- direction of the line. Alternatively, when bending is switched on,
- even more complicated low-level transformations will be done
- automatically.
-
- The are some special considerations concerning the \meta{code}:
- %
- \begin{itemize}
- \item In the \meta{code} you may \emph{not} use |\pgfusepath|
- since this would try to add arrow tips to the arrow tip and
- lead to a recursion. Use the ``quick'' versions
- |\pgfusepathqstroke| and so on instead, which never try to
- add arrow tips.
- \item If you stroke the path that you construct, you should
- first set the dashing to solid and set up fixed joins and
- caps, as needed. This will ensure that the arrow tip will
- always look the same.
- \item When the arrow tip code is executed, it is automatically
- put inside a low-level scope, so nothing will ``leak out''
- from the scope.
- \item The high-level coordinate transformation matrix will be
- set to the identity matrix when the code is executed for
- the first time.
- \end{itemize}
- \item \declare{|cache|}|=|\meta{true or false}
-
- When set to |true|, which is the default, the \meta{code} will be
- executed only once for a particular value of parameters and the
- low-level commands created by the drawing code (using the system
- layer protocol subsystem, see Section~\ref{section-protocols}) will
- be cached and reused later on. However, when the drawing code
- contains ``uncachable'' code like a call to |\pgftext|, caching
- must be switched off by saying |cache=false|.
- \item \declare{|bending mode|}|=|\meta{mode}
-
- This key is important only when the |bend| option is used with an
- arrow, see Section~\ref{section-arrow-flex} for an introduction to
- this option. The |bend| option asks us to, well, bend the arrow
- head. For some arrow head this is not possible or leads to very
- strange drawings (for instance, when the |\pgftext| command is
- used) and then it is better to switch bending off for the arrow
- head (|flex| will then be used instead). To achieve this, set
- \meta{mode} to |none|.
-
- For most arrow tips it does, however, make sense to bend them.
- There are (at least) two different mathematical ways of doing so,
- see Section~\ref{section-library-curvilinear} for details. Which of
- these ways is use can be configured by setting \meta{mode} to
- either |orthogonal| or to |polar|. It is best to try simply try out
- both when designing an arrow tip to see which works better. Since
- |orthogonal| is quicker and often gives good oder even better
- results, it is the default. Some arrow tips, however, profit from
- saying |bending mode=polar|.
- \item \declare{|defaults|}|=|\meta{arrow keys}
-
- The \meta{arrow keys} allow you to configure the default values for
- the parameters on which an arrow tip depends. The \meta{arrow keys}
- will be executed first before any other arrow tip options are
- executed, see Section~\ref{section-arrow-scopes} for the exact
- sequence. Also see Section~\ref{section-arrow-options} below for
- more details on arrow options.
- \end{itemize}
-
- This concludes the description of the keys you provide for the declaration
- of an arrow. Let us now have a look at a simple example that uses these
- features: We want to define an arrow tip kind |foo| that produces the arrow
- tip we used as our running example. However, to make things a bit more
- interesting, let us make it ``configurable'' insofar as the length of the
- arrow tip can be configured using the |length| option, which sets the
- |\pgfarrowlength|. By default, this length should be the gigantic 4cm we
- say in the example, but uses should be able to set it to anything they
- like. We will not worry about the arrow width or insets, of arrow line
- width, or harpoons, or anything else in this example to keep it simple.
-
- Here is the code:
- %
-\begin{codeexample}[code only]
-\pgfdeclarearrow{
- name = foo,
- parameters = { \the\pgfarrowlength },
- setup code = {
- % The different end values:
- \pgfarrowssettipend{.25\pgfarrowlength}
- \pgfarrowssetlineend{-.25\pgfarrowlength}
- \pgfarrowssetvisualbackend{-.5\pgfarrowlength}
- \pgfarrowssetbackend{-.75\pgfarrowlength}
- % The hull
- \pgfarrowshullpoint{.25\pgfarrowlength}{0pt}
- \pgfarrowshullpoint{-.75\pgfarrowlength}{.5\pgfarrowlength}
- \pgfarrowshullpoint{-.75\pgfarrowlength}{-.5\pgfarrowlength}
- % Saves: Only the length:
- \pgfarrowssavethe\pgfarrowlength
- },
- drawing code = {
- \pgfpathmoveto{\pgfqpoint{.25\pgfarrowlength}{0pt}}
- \pgfpathlineto{\pgfqpoint{-.75\pgfarrowlength}{.5\pgfarrowlength}}
- \pgfpathlineto{\pgfqpoint{-.5\pgfarrowlength}{0pt}}
- \pgfpathlineto{\pgfqpoint{-.75\pgfarrowlength}{-.5\pgfarrowlength}}
- \pgfpathclose
- \pgfusepathqfill
- },
- defaults = { length = 4cm }
-}
-\end{codeexample}
- %
- We can now use it:
- %
-\pgfdeclarearrow{
- name = foo,
- parameters = { \the\pgfarrowlength },
- setup code = {
- % The different end values:
- \pgfarrowssettipend{.25\pgfarrowlength}
- \pgfarrowssetlineend{-.25\pgfarrowlength}
- \pgfarrowssetvisualbackend{-.5\pgfarrowlength}
- \pgfarrowssetbackend{-.75\pgfarrowlength}
- % The hull
- \pgfarrowshullpoint{.25\pgfarrowlength}{0pt}
- \pgfarrowshullpoint{-.75\pgfarrowlength}{.5\pgfarrowlength}
- \pgfarrowshullpoint{-.75\pgfarrowlength}{-.5\pgfarrowlength}
- % Saves: Only the length:
- \pgfarrowssavethe\pgfarrowlength
- },
- drawing code = {
- \pgfpathmoveto{\pgfqpoint{.25\pgfarrowlength}{0pt}}
- \pgfpathlineto{\pgfqpoint{-.75\pgfarrowlength}{.5\pgfarrowlength}}
- \pgfpathlineto{\pgfqpoint{-.5\pgfarrowlength}{0pt}}
- \pgfpathlineto{\pgfqpoint{-.75\pgfarrowlength}{-.5\pgfarrowlength}}
- \pgfpathclose
- \pgfusepathqfill
- },
- defaults = { length = 4cm }
-}
-\begin{codeexample}[
- preamble={\usetikzlibrary{arrows.meta}},
- pre={\pgfdeclarearrow{
- name = foo,
- parameters = { \the\pgfarrowlength },
- setup code = {
- % The different end values:
- \pgfarrowssettipend{.25\pgfarrowlength}
- \pgfarrowssetlineend{-.25\pgfarrowlength}
- \pgfarrowssetvisualbackend{-.5\pgfarrowlength}
- \pgfarrowssetbackend{-.75\pgfarrowlength}
- % The hull
- \pgfarrowshullpoint{.25\pgfarrowlength}{0pt}
- \pgfarrowshullpoint{-.75\pgfarrowlength}{.5\pgfarrowlength}
- \pgfarrowshullpoint{-.75\pgfarrowlength}{-.5\pgfarrowlength}
- % Saves: Only the length:
- \pgfarrowssavethe\pgfarrowlength
- },
- drawing code = {
- \pgfpathmoveto{\pgfqpoint{.25\pgfarrowlength}{0pt}}
- \pgfpathlineto{\pgfqpoint{-.75\pgfarrowlength}{.5\pgfarrowlength}}
- \pgfpathlineto{\pgfqpoint{-.5\pgfarrowlength}{0pt}}
- \pgfpathlineto{\pgfqpoint{-.75\pgfarrowlength}{-.5\pgfarrowlength}}
- \pgfpathclose
- \pgfusepathqfill
- },
- defaults = { length = 4cm }
-}},
-]
-\tikz \draw [-foo] (0,0) -- (8,0);
-\end{codeexample}
-\begin{codeexample}[
- preamble={\usetikzlibrary{arrows.meta,bending}},
- pre={\pgfdeclarearrow{
- name = foo,
- parameters = { \the\pgfarrowlength },
- setup code = {
- % The different end values:
- \pgfarrowssettipend{.25\pgfarrowlength}
- \pgfarrowssetlineend{-.25\pgfarrowlength}
- \pgfarrowssetvisualbackend{-.5\pgfarrowlength}
- \pgfarrowssetbackend{-.75\pgfarrowlength}
- % The hull
- \pgfarrowshullpoint{.25\pgfarrowlength}{0pt}
- \pgfarrowshullpoint{-.75\pgfarrowlength}{.5\pgfarrowlength}
- \pgfarrowshullpoint{-.75\pgfarrowlength}{-.5\pgfarrowlength}
- % Saves: Only the length:
- \pgfarrowssavethe\pgfarrowlength
- },
- drawing code = {
- \pgfpathmoveto{\pgfqpoint{.25\pgfarrowlength}{0pt}}
- \pgfpathlineto{\pgfqpoint{-.75\pgfarrowlength}{.5\pgfarrowlength}}
- \pgfpathlineto{\pgfqpoint{-.5\pgfarrowlength}{0pt}}
- \pgfpathlineto{\pgfqpoint{-.75\pgfarrowlength}{-.5\pgfarrowlength}}
- \pgfpathclose
- \pgfusepathqfill
- },
- defaults = { length = 4cm }
-}},
-]
-\tikz \draw [-{foo[length=2cm,bend]}] (0,0) to [bend left] (3,0);
-\end{codeexample}
-
-
- \medskip
- \noindent\textbf{Defining a Shorthand.}
- The |\pgfdeclarearrow| command can also used to define
- \emph{shorthands}. This works as follows:
- \begin{itemize}
- \item First, you must provide a |name| just in the same way as when you
- define a full-flung new arrow tip kind.
- \item Second, instead of all of the other options listed above, you
- just use one more option:
-
- \smallskip
- \declare{|means|}|=|\meta{end arrow specification}
-
- This sets up things so that whenever \meta{name} is now used in an
- arrow specification, it will be replaced by the \meta{end arrow
- specification} (the problems resulting form the \meta{name} begin
- used in a start arrow specification are taken care of
- automatically). See also Section~\ref{section-arrow-tip-macro} for
- details on the order in which options get executed in such cases.
-
- Note that the \meta{end arrow specification} will be executed
- immediately to build the so-called arrow option caches, a concept
- explored in more detail in
- Section~\ref{section-arrow-option-cache}. In practice, this has
- mainly two effects: First, all arrow tips referred to in the
- specification must already exist (at least as ``dummy'' versions).
- Second, all dimensions mentioned in options of the \meta{end arrow
- specification} will be evaluated immediately. For instance, when
- you write
- %
-\begin{codeexample}[code only]
-\pgfdeclarearrow{ name=foo, means = bar[length=2cm+\mydimen] }
-\end{codeexample}
- %
- The value |2cm+\mydimen| is evaluated immediately. When |foo| is
- used later on and |\mydimen| has changed, this has no effect.
- \end{itemize}
-\end{command}
-
-
-\subsection{Handling Arrow Options}
-\label{section-arrow-options}
-
-When you declare an arrow tip, your drawing code should take into account the
-different arrow keys set for it (like the arrow tip length, width, or
-harpooning). The different arrow keys that are available have been described in
-detail in Section~\ref{section-arrow-config}; but how do we access the values
-set by an option like |length| or |harpoon| or |bend| in the drawing code? In
-the present section we have a look at how this works.
-
-
-\subsubsection{Dimension Options}
-
-Most arrow keys, like |length| or |width'|, simple set a \TeX\ dimension
-register to a certain value. For example, |length| sets the value of the \TeX\
-dimension register |\pgfarrowlength|. Note that |length| takes several values
-as input with a complicated semantics as explained for the |length| key on
-page~\pageref{length-arrow-key}. All of these settings are not important for
-the setup code: When it gets executed, the code behind the |length| key will
-have computed a simple number that is stored in |\pgfarrowlength|. Indeed,
-inside the setup code you do not have access to the exact value given to the
-|length| key; just to the final computed value.
-
-The following \TeX\ dimensions are available to the setup code:
-%
-\begin{itemize}
- \item |\pgfarrowslength|. It gets set by the arrow keys |length| and
- |angle|.
- \item |\pgfarrowswidth|. It gets set by |width|, |width'|, and |angle|.
- \item |\pgfarrowsinset|. It gets set by |inset| and |inset'|.
- \item |\pgfarrowslinewidth|. It gets set by |line width| and |line width'|.
-\end{itemize}
-
-If your setup code depends on any of them, add them to the |parameters| key of
-the arrow tip.
-
-
-\subsubsection{True--False Options}
-
-A number of arrow keys just do a yes/no switch, like |reversed|. All of them
-setup a \TeX-if that you can access in the setup code:
-%
-\begin{itemize}
- \item |\ifpgfarrowreversed| is setup by |reversed|.
- \item |\ifpgfarrowswap| is setup by |swap| and also |right|.
- \item |\ifpgfarrowharpoon| is setup by |harpoon| and also |left| and
- |right|.
- \item |\ifpgfarrowroundcap| is set to true by |line cap=round| and set to
- false by |line cap=butt|. It also gets (re)set by |round| and |sharp|.
- \item |\ifpgfarrowroundjoin| is set to true by |line join=round| and set to
- false by |line join=miter|. It also gets (re)set by |round| and
- |sharp|.
- \item |\ifpgfarrowopen| is set to true by |fill=none| and by |open| (which
- is a shorthand for |fill=none|) and set to false by |color| and all
- other |fill=|\meta{color}.
-\end{itemize}
-
-If you code depends on any of these, you must add them to the |parameters| in
-such a way that the parameters are different when the \TeX-if is set from when
-it is not set. An easy way to achieve this is to write something like
-%
-\begin{codeexample}[code only]
- parameters = { \the\pgfarrowlength,...,
- \ifpgfarrowharpoon h\fi\
- \ifpgfarrowroundjoin j\fi}
-\end{codeexample}
-%
-In other words, for each set parameter on which the arrow tip depends, a
-specific letter is added to the parameters, making them unique.
-
-The first two of the above keys are a bit special: Reversing and swapping an
-arrow tip can be done just by fiddling with the transformation matrix: a
-reverse is a ``flip'' along the $y$-axis and a swap is a flip along the
-$x$-axis. This is done automatically by \pgfname.
-
-Nevertheless, you may wish to modify you code in dependence especially of the
-|reverse| key: When |\ifpgfarrowreverse| is true, \pgfname\ will flip the
-coordinate system along the $y$-axis, will negate all end values (like line
-end, tip end, and so on) and will exchange the meaning of back end and tip end
-as well as of visual back end and visual back end. Usually, this is exactly
-what one need; \emph{except} that the line end may no longer be appropriate.
-After all, the line end should be chosen so that it is completely covered by
-the arrow. Now, when the arrow tip is open, a reversed arrow should no longer
-have the line end near the old visual back end, but near to the old visual tip
-end.
-
-For these reasons, you may need to make the computation of the line end
-dependent on whether the arrow is reversed or not. Note that when you specify a
-different line end for a reversed arrow tip, the transformation and inverting
-of the coordinate system will still be done, meaning that if |reverse| is true,
-you need to specify a line end in the ``old'' coordinate system that is at the
-position where, after everything is inverted, it will be at the correct
-position. Usually that means that if the |reverse| option is set, you need to
-\emph{increase} the line end.
-
-
-\subsubsection{Inaccessible Options}
-
-There are some options that influence the way an arrow tip looks, but that you
-cannot access inside the setup code. Handling these options lies entirely with
-\pgfname. If you wish your setup code to handle these options, you have to
-setup your own ``parallel'' options.
-%
-\begin{itemize}
- \item |quick|, |flex|, |flex'|, and |bend| are all handled automatically.
- You can, however, set the |bending mode| to avoid bending of your arrow
- tip.
- \item The colors set by |color| and |fill|. You can, however, access them
- indirectly, namely through the current stroke and fill colors.
- \item |sep|
-\end{itemize}
-
-
-\subsubsection{Defining New Arrow Keys}
-\label{section-arrow-option-cache}
-
-The set of predefined options is already quite long and most arrow tips will
-not need more than the predefined options. However, sometimes an arrow tip may
-need to introduce a new special-purpose option. For instance, suppose we wish
-to introduce a new fictive arrow key |depth|. In such cases, you must do two
-things:
-%
-\begin{enumerate}
- \item Introduce a new dimension register or macro that will hold the
- configuration value and which will be accessed by the setup code. The
- could be achieved by saying
- %
-\begin{codeexample}[code only]
-\newdimen\pgfarrowdepth
-\end{codeexample}
- %
- \item Introduce a new arrow key option |/pgf/arrow keys/depth| that allows
- users to configure the new macro or register.
-\end{enumerate}
-
-When an arrow is selected via for instance |foo[depth=5pt]|, the key--value
-pairs between the square brackets are executed with the path prefix
-|/pgf/arrow keys|. Thus, in the example, our depth key would get executed.
-Thus, it is tempting to write something like
-%
-\begin{codeexample}[code only]
-\pgfkeys{/pgf/arrow keys/depth/.code = \pgfmathsetlength{\pgfarrowdepth}{#1}}
-\end{codeexample}
-
-Sadly, this will not work. The reason is that there is yet another level of
-caching involved when \pgfname\ processes arrow tips: The option cache! The
-problem is each time an arrow tip is used, even when the drawing code of the
-arrow tip is nicely cached, we still need to process the options in
-|foo[length=5pt]| to find out which version in the cache we would like to
-access. To make matters worse, |foo| might be a shorthand that calls other
-arrow tips, which add more options, and so on. Unfortunately, executing keys is
-quite an expensive operation (\pgfname's key--value parser is powerful, but
-that power comes at a price). So, whenever possible, we do \emph{not} want the
-key--value parser to be started.
-
-For these reasons, when something like |foo[|\meta{options}|]| is encountered
-inside a shorthand, the \meta{options} are executed only once. They should now
-setup the \emph{arrow option cache}, which is some code that, when executed,
-should setup the values that the \meta{options} configure. In our example, the
-|depth| key should add something to the arrow option cache that sets
-|\pgfarrowdepth| to the given value.
-
-Adding something to the arrow option cache is done using the following command:
-
-\begin{command}{\pgfarrowsaddtooptions\marg{code}}
- This command should be called by keys with the prefix |/pgf/arrow keys| to
- add code to the arrow option cache. For our |depth| key example, we could
- use this key as follows:
- %
-\begin{codeexample}[code only]
-\pgfkeys{/pgf/arrow keys/depth/.code=
- \pgfarrowsaddtooptions{\pgfmathsetlength{\pgfarrowdepth}{#1}}
-\end{codeexample}
- %
- Actually, this is still not optimal since the expensive |\pgfmathsetlength|
- command is now called each time an arrow tip is used with the |depth|
- option set. The trick is to do the expensive operation only once and then
- store only very quick code in the arrow option cache:
- %
-\begin{codeexample}[code only]
-\pgfkeys{/pgf/arrow keys/depth/.code=
- \pgfmathsetlength{\somedimen}{#1}
- \pgfarrowsaddtooptions{\pgfarrowdepth=\somedimen} % buggy
-\end{codeexample}
- %
- The above code will not (yet) work since |\somedimen| will surely have a
- different value when the cache is executed. The trick is to use some
- |\expandafter|s:
- %
-\begin{codeexample}[code only]
-\pgfkeys{/pgf/arrow keys/depth/.code=
- \pgfmathsetlength{\somedimen}{#1}
- \expandafter\pgfarrowsaddtooptions\expandafter{\expandafter\pgfarrowdepth\expandafter=\the\somedimen}
-\end{codeexample}
- %
-\end{command}
-
-\begin{command}{\pgfarrowsaddtolateoptions\marg{code}}
- This command works like |\pgfarrowsaddtooptions|, only the \meta{code} will
- be executed ``later'' than the code added by the normal version of the
- command. This is useful for keys that depend on the length of an arrow:
- Keys like |width'| want to define the arrow width as a multiple of the
- arrow length, but when the |width'| key is given, the length may not yet
- have been specified. By making the computation of the width a ``late''
- option, we ensure that |\pgfarrowlength| will have been setup correctly.
-\end{command}
-
-If you define a new option that sets a dimensions and if that dimension should
-change in accordance to the setting of either |scale length| or |scale width|,
-you need to make \pgfname\ ``aware'' of this using the following key:
-
-\begin{command}{\pgfarrowsaddtolengthscalelist\marg{dimension register}}
- Each time an arrow tip is used, the given \meta{dimension register} will be
- multiplied by the |scale length| factor prior to the actual drawing. You
- call this command only once in the preamble somewhere.
-\end{command}
-
-\begin{command}{\pgfarrowsaddtowidthscalelist\marg{dimension register}}
- Works like |\pgfarrowsaddtolengthscalelist|, only for width parameters.
-\end{command}
-
-
-\begin{command}{\pgfarrowsthreeparameters\marg{line-width dependent size specification}}
- This command is useful for parsing the values given to keys like |length|
- or |width| the expect a dimension followed optionally for some numbers.
- This command converts the \meta{line-width dependent size specification},
- which may consist of one, two, or three numbers, into a triple of three
- numbers in curly braces, which gets stored in the macro
- |\pgfarrowstheparameters|. Here is an example, where |\showvalueofmacro| is
- used in this example to show the value stored in a macro:
- %
-\begin{codeexample}[setup code,hidden]
- \makeatletter
- \def\showvalueofmacro#1{%
- \texttt{\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\pgfutil@gobble\expandafter\expandafter\expandafter\string\expandafter\csname#1\endcsname}
- }%
-\end{codeexample}
-%
-\begin{codeexample}[]
-\pgfarrowsthreeparameters{2pt 1}
-\showvalueofmacro\pgfarrowstheparameters
-\end{codeexample}
- %
-\end{command}
-
-\begin{command}{\pgfarrowslinewidthdependent\marg{dimension}\marg{line width factor}\marg{outer factor}}
- This command takes three parameters and does the ``line width dependent
- computation'' described on page~\pageref{length-arrow-key} for the |length|
- key. The result is returned in |\pgf@x|.
-
- The idea is that you can setup line-width dependent keys like |length| or
- |width| using code like the following:
- %
-\begin{codeexample}[code only]
-\pgfkeys{/pgf/arrow keys/depth/.code={%
- \pgfarrowsthreeparameters{#1}%
- \expandafter\pgfarrowsaddtolateoptions\expandafter{%
- \expandafter\pgfarrowslinewidthdependent\pgfarrowstheparameters% compute...
- \pgfarrowdepth\pgf@x% ... and store.
- }%
-}
-\end{codeexample}
- %
-\end{command}
-
-\begin{command}{\pgfarrowslengthdependent\marg{dimension}\marg{length factor}\marg{dummy}}
- This command takes three parameters, of which the last one is ignored, and
- does the ``length dependent computation'' described for the |width'| and
- |inset'| keys. The result is returned in |\pgf@x|.
-
- You can setup length dependent keys using code like the following:
- %
-\begin{codeexample}[code only]
-\pgfkeys{/pgf/arrow keys/depth'/.code={%
- \pgfarrowsthreeparameters{#1}%
- \expandafter\pgfarrowsaddtolateoptions\expandafter{%
- \expandafter\pgfarrowslengthdependent\pgfarrowstheparameters% compute...
- \pgfarrowdepth\pgf@x% ... and store.
- }%
-}
-\end{codeexample}
- %
-\end{command}
-
-
-%%% Local Variables:
-%%% mode: latex
-%%% TeX-master: "pgfmanual"
-%%% End: