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-<HTML>
-<HEAD>
-<!-- Created by texi2html 1.56k from texdraw.texi on 10 March 2004 -->
-
-<TITLE>TeXdraw - 5. More Details</TITLE>
-</HEAD>
-<BODY>
-Go to the <A HREF="texdraw_1.html">first</A>, <A HREF="texdraw_4.html">previous</A>, <A HREF="texdraw_6.html">next</A>, <A HREF="texdraw_11.html">last</A> section, <A HREF="texdraw_toc.html">table of contents</A>.
-<P><HR><P>
-
-
-<H1><A NAME="SEC22" HREF="texdraw_toc.html#TOC22">5. More Details</A></H1>
-
-<P>
-The first part of this chapter offers some suggestions for strategies to
-isolate errors in TeX and TeXdraw input. The second part of this
-chapter discusses implementational issues. An awareness of these issues
-is useful if TeXdraw is to be extended.
-
-
-
-<UL>
-<LI><A HREF="texdraw_5.html#SEC23">Errors while using TeXdraw</A>
-<LI><A HREF="texdraw_5.html#SEC24">Extending TeXdraw</A>
-<LI><A HREF="texdraw_5.html#SEC29">How TeXdraw merges graphics and text</A>
-</UL>
-
-
-
-<H2><A NAME="SEC23" HREF="texdraw_toc.html#TOC23">5.1 Errors while using TeXdraw</A></H2>
-<P>
-<A NAME="IDX119"></A>
-<A NAME="IDX120"></A>
-
-
-<P>
-TeX input is notoriously difficult to debug. If TeX reports
-errors, so much the better. If the cause is not immediately obvious,
-consider using a binary search strategy, removing sections of code with
-the premature insertion of the <CODE>\bye</CODE> (or <CODE>\end{document}</CODE>
-for LaTeX) command (with the appropriate closing of any open groups
-and the like). Other strategies include the insertion of
-<CODE>\message{I am here}</CODE> at appropriate places. Try using
-<CODE>\tracingmacros=1</CODE>. Many problems turn out to be due to an
-incorrect number of macro arguments or incorrectly delimited macro
-arguments. The <CODE>\tracingmacros=1</CODE> option writes the macro
-arguments and macro expansions to the TeX log file.
-
-
-<P>
-Certain errors may not manifest themselves until well after the
-offending command. For instance, if a closing parenthesis is missing
-from a TeXdraw coordinate, TeX continues searching for the
-parenthesis. If one is found, perhaps many lines later, the TeXdraw
-error message <CODE>invalid coordinate</CODE> will be printed at this later
-point.
-
-
-<P>
-All input in the TeXdraw environment should be intended for
-interpretation by TeXdraw commands. TeXdraw places text inside a
-zero size box (the text itself extends outside the box). Extraneous
-input manifests itself as a non-zero size TeXdraw text box. This
-causes the TeXdraw text and the PostScript graphics to be displaced
-from one another. An error message is issued if a non-zero width
-TeXdraw text box is detected. If this error message appears, look
-for unintended character sequences amongst the commands to TeXdraw.
-
-
-<P>
-Several TeXdraw commands pass their arguments "raw" to the
-PostScript file. That means that invalid arguments can generate
-PostScript errors when the document is printed. For instance the
-argument of the <CODE>\setgray</CODE> command is passed straight through to
-the PostScript file. If this argument is non-numeric, a PostScript
-error results. Not all PostScript printers report errors back to the
-user. The print may just stop prematurely. One approach to debugging
-is to use a PostScript previewer on a workstation. That way, one can
-determine at which point in the drawing the PostScript error occurs.
-
-
-
-
-<H2><A NAME="SEC24" HREF="texdraw_toc.html#TOC24">5.2 Extending TeXdraw</A></H2>
-<P>
-<A NAME="IDX121"></A>
-
-
-<P>
-TeXdraw is implemented using a combination of TeX commands and
-PostScript code. This section discusses some of the implementational
-issues as they relate to extending TeXdraw.
-
-
-<P>
-TeXdraw as implemented, offers a basic set of drawing features.
-These are adequate for certain tasks such as producing block diagrams.
-There are different approaches to extending TeXdraw to include other
-functions. In some cases, the desired functionality can be achieved by
-writing a TeX macro which builds on top of the existing TeXdraw
-commands. As these extensions become more complex, the limitations of
-TeX for computations become increasingly evident. In other cases,
-access to different features of PostScript is desired. The appropriate
-approach would be to write new PostScript procedures which can be
-accessed by TeX macros.
-
-
-<P>
-Included with TeXdraw is a set of macros for directly accessing
-PostScript functions. These are described in an appendix
-(see section <A HREF="texdraw_6.html#SEC30">A. PostScript Commands</A>).
-
-
-<P>
-TeXdraw also comes with a toolbox of routines for handling much of
-the user interface, converting between different coordinate
-representations and the like. The macros for coordinate decoding and
-for computations involving coordinates are described in an appendix
-(see section <A HREF="texdraw_7.html#SEC31">B. TeXdraw Toolbox</A>).
-
-
-
-<UL>
-<LI><A HREF="texdraw_5.html#SEC25">Scaling</A>
-<LI><A HREF="texdraw_5.html#SEC26">Resolution</A>
-<LI><A HREF="texdraw_5.html#SEC27">Text placement</A>
-<LI><A HREF="texdraw_5.html#SEC28">Intermediate PostScript file</A>
-</UL>
-
-
-
-<H3><A NAME="SEC25" HREF="texdraw_toc.html#TOC25">5.2.1 Scaling</A></H3>
-<P>
-<A NAME="IDX122"></A>
-
-
-<P>
-The scaling commands provided in TeXdraw are designed to affect only
-the coordinate values specified in commands. For instance, changing the
-<CODE>\setunitscale</CODE> value changes the interpretation of the coordinate
-in an <CODE>\avec (<VAR>x</VAR> <VAR>y</VAR>)</CODE> command, but does not change the
-line width or arrowhead sizes in effect. None of the TeXdraw scaling
-commands affect the size of TeX text produced by, for instance, the
-<CODE>\htext</CODE> command. Scale changes will however affect the
-positioning of text for subsequent commands.
-
-
-<P>
-The line parameters are changed only if the corresponding commands to
-change them are issued. If the <CODE>\linewd</CODE> command is given, the
-current coordinate scaling is used to determine the line width. To
-achieve a behaviour more like a global scaling, whenever the scale
-factor is changed, the line parameters should be set again.
-
-
-
-
-<H3><A NAME="SEC26" HREF="texdraw_toc.html#TOC26">5.2.2 Resolution</A></H3>
-<P>
-<A NAME="IDX123"></A>
-
-
-<P>
-TeXdraw scales coordinates before passing them to PostScript.
-Keeping track of the coordinate scaling is necessary, in any event, to
-allow TeXdraw to compute the maximum excursions of the coordinates.
-TeXdraw uses pixel units in its PostScript code. One pixel unit is
-equal to 1/300 of an inch. TeXdraw issues PostScript commands with
-integer valued pixel coordinates. This sets the positioning resolution
-for TeXdraw. The passing of integer valued coordinates which
-correspond to the device resolution keeps lines aligned with the device
-grid; parallel lines of the same width will be rendered with the same
-width.
-
-
-<P>
-The position saving mechanism in TeXdraw (see section <A HREF="texdraw_3.html#SEC16">3.3 Saving positions</A>)
-associates the pixel coordinates of a position with the specified name.
-
-
-<P>
-TeXdraw uses the limited real number representation provided by
-TeX. These operations are based on the representation of dimensions
-as real-valued numbers of points. Internally in TeX, dimensions are
-stored 32-bit values, normalized so that 1 pt corresponds to the scaled
-point (sp) value of 65536. Dimensions with magnitudes between 0.000015
-pt and 32767 pt can be represented. This is also the dynamic range of
-the TeXdraw pixel coordinates passed to PostScript. TeXdraw must
-convert from user supplied coordinates using the scaling factor (which
-itself consists of two components, the unit scale and the segment scale)
-and a pixel conversion factor. The use of limited precision real
-numbers in these computations can cause accumulation of error when
-relative scaling is used repeatedly.
-
-
-
-
-<H3><A NAME="SEC27" HREF="texdraw_toc.html#TOC27">5.2.3 Text placement</A></H3>
-
-<P>
-While in the TeXdraw environment, TeX text is placed in a TeX
-box while PostScript code is written to the intermediate file. At the
-end of the TeXdraw environment, the size of the drawing is
-determined. A TeX box of this size is created. The TeX
-<CODE>\special</CODE> mechanism is used to instruct the PostScript driver
-program to position the PostScript drawing from the intermediate file in
-this area. Next, the text generated by TeXdraw is positioned and
-placed in the box. Note that when the document is printed, the
-PostScript drawing is placed on the page before the TeX text; TeX
-text will appear on top of graphics.
-
-
-<P>
-<A NAME="IDX124"></A>
-<A NAME="IDX125"></A>
-The rotation of text is carried out with in-line PostScript code which
-does not appear in the intermediate PostScript file. This code is sent
-to the PostScript driver with a <CODE>\special</CODE> command. This
-PostScript code is embedded in the dvi (device independent) file that
-TeX produces.
-
-
-
-
-<H3><A NAME="SEC28" HREF="texdraw_toc.html#TOC28">5.2.4 The intermediate PostScript file</A></H3>
-<P>
-<A NAME="IDX126"></A>
-
-
-<P>
-The intermediate PostScript file consists of a header, a body and a
-trailer following Encapsulated PostScript File (EPSF) standards. The
-header sets up PostScript definitions and default parameter values. The
-trailer includes the <CODE>BoundingBox</CODE> information which gives the
-coordinates in default PostScript units (72 per inch) for the lower
-lefthand corner and the upper righthand corner of the drawing. The body
-of the intermediate PostScript file contains the PostScript commands
-generated by TeXdraw.
-
-
-<P>
-Many moves in TeXdraw serve only to position text or to reset saved
-positions. TeXdraw buffers move commands in order to be able to
-collapse runs of moves. Only the last move of a run of moves is
-actually written to the PostScript file. However the intermediate moves
-still affect the size of the drawing. The expunging of moves means that
-the PostScript file <CODE>BoundingBox</CODE> information may indicate a drawing size
-larger than the PostScript commands themselves would warrant.
-
-
-<P>
-Drawing segments in TeXdraw show up in the PostScript file as saves
-and restores of the PostScript graphics state. Segment starts are
-buffered and only written out if necessary. This way "empty" segments
-do not generate output to the PostScript file. These empty segments
-arise if a segment contains only moves and text commands. The moves
-inside the segment are not needed since they are local to the segment,
-and the text commands do not generate output to the PostScript file.
-
-
-<P>
-If TeXdraw is used only for moves and text, no intermediate
-PostScript file will be created.
-
-
-
-
-<H2><A NAME="SEC29" HREF="texdraw_toc.html#TOC29">5.3 How TeXdraw merges graphics and text</A></H2>
-<P>
-<A NAME="IDX127"></A>
-<A NAME="IDX128"></A>
-<A NAME="IDX129"></A>
-
-
-<P>
-TeXdraw creates a box which is the same size as the graphic. The
-printer driver will place the PostScript graphic into this space. Any
-TeX text generated by the TeXdraw commands will be superimposed on
-this graphic.
-
-
-<P>
-<A NAME="IDX130"></A>
-<A NAME="IDX131"></A>
-The LaTeX2e front-end for TeXdraw is enabled by including the
-<CODE>texdraw</CODE> package. The <CODE>texdraw</CODE> package automatically
-invokes the standard <CODE>graphics</CODE> package distributed with
-LaTeX2e. The <CODE>graphics</CODE> package has support for a number of
-different printer drivers, including a number for PostScript printers.
-Any options to the <CODE>texdraw</CODE> package are passed on to the
-<CODE>graphics</CODE> package. Such an option can be used to select a driver
-other than the default one.
-
-
-<P>
-<A NAME="IDX132"></A>
-<A NAME="IDX133"></A>
-<A NAME="IDX134"></A>
-<A NAME="IDX135"></A>
-<A NAME="IDX136"></A>
-Within the <CODE>graphics</CODE> package, the driver option is used to select
-definitions for the low-level macros which generate the <CODE>\special</CODE>
-commands needed to request insertion of a graphics file and to rotate
-text.<A NAME="DOCF2" HREF="texdraw_foot.html#FOOT2">(2)</A>
-TeXdraw uses the user-level macros defined by the <CODE>graphics</CODE>
-package (see section <A HREF="texdraw_4.html#SEC21">4.1 PostScript printer drivers</A>). When not used with the
-LaTeX2e front-end, TeXdraw defines versions of these macros that
-are suitable for use with the <CODE>dvips</CODE> printer driver.
-
-
-<P><HR><P>
-Go to the <A HREF="texdraw_1.html">first</A>, <A HREF="texdraw_4.html">previous</A>, <A HREF="texdraw_6.html">next</A>, <A HREF="texdraw_11.html">last</A> section, <A HREF="texdraw_toc.html">table of contents</A>.
-</BODY>
-</HTML>