1 .\" For tolerably obvious reason, this needs to be processed through PIC.
2 .\" It also needs to be processed through TBL and EQN. Use "groff -p -e -t".
3 .\" There is no hope that this will ever look right under nroff.
5 .\" Comments beginning with %% are cut lines so portions of this
6 .\" document can be automatically extracted. %%TUTORIAL%% begins the
7 .\" tutorial part; %%REFERENCE%% the reference part. %%POSTLUDE%% the
8 .\" bibliography and end matter after the reference part.
10 .\" This document was written for free use and redistribution by
11 .\" Eric S. Raymond <esr@thyrsus.com> in August 1995.
15 .\" Set a proper TeX and LaTeX
17 . ds tx T\h'-.1667m'\v'.224m'E\v'-.224m'\h'-.125m'X\"
18 . ds lx L\h'-0.36m'\v'-0.22v'\s-2A\s0\h'-0.15m'\v'0.22v'\*(tx\"
25 .de CE\" Centered caption for figure. Assumes previous .KS
31 .\" Definitions end here
33 Making Pictures With GNU PIC
37 \[la]\fIesr@snark.thyrsus.com\fP\[ra]
39 The \fBpic\fP language is a \fBtroff\fP extension that makes it easy
40 to create and alter box-and-arrow diagrams of the kind frequently used
41 in technical papers and textbooks. This paper is both an introduction
42 to and reference for \fIgpic\/\fP(1), the implementation distributed by
43 the Free Software Foundation for use with \fIgroff\/\fP(1).
54 The \fBpic\fP language provides an easy way to write procedural
55 box-and-arrow diagrams to be included in \fBtroff\fP documents. The
56 language is sufficiently flexible to be quite useful for state charts,
57 Petri-net diagrams, flow charts, simple circuit schematics, jumper
58 layouts, and other kinds of illustration involving repetitive uses of
59 simple geometric forms and splines. Because these descriptions are
60 procedural and object-based, they are both compact and easy to modify.
62 The \fIgpic\/\fP(1) implementation of \fBpic\fP is distributed by the
63 Free Software Foundation for use with their \fIgroff\/\fP(1)
64 implementation of \fBtroff\fP. Because both implementations are
65 widely available in source form for free, they are good bets for
66 writing very portable documentation.
71 The original 1984 pre-\fIditroff\/\fP(1) version of \fBpic\fP is long
72 obsolete. The rewritten 1991 version is still available as part of
73 the Documenter's Work Bench module of System V.
75 Where differences between Documenter's Work Bench (1991) \fBpic\fP and GNU
76 \fBpic\fP need to be described, original \fBpic\fP is referred to as
77 \[lq]DWB pic\[rq]. Details on the history of the program are given at the
80 In this document, the \fIgpic\/\fP(1) extensions will be marked as such.
86 Every \fBpic\fP description is a little program, which gets compiled
87 by \fIpic\/\fP(1) into \fIgtroff\/\fP(1) macros. Programs that process or
88 display \fIgtroff\/\fP(1) output need not know or care that parts of the
89 image began life as \fBpic\fP descriptions.
91 The \fIpic\/\fP(1) program tries to translate anything between \fB.PS\fP
92 and \fB.PE\fP markers, and passes through everything else. The normal
93 definitions of \fB.PS\fP and \fB.PE\fP in the \fIms\fP macro package
94 and elsewhere have also the side-effect of centering the \fBpic\fP output
100 If you make a \fBpic\fP syntax error, \fIgpic\/\fP(1) will issue an
101 error message in the standard \fIgcc\/\fP(1)-like syntax. A typical
102 error message looks like this,
106 pic:pic.ms:<nnn>: parse error before `<token>'
107 pic:pic.ms:<nnn>: giving up on this picture
112 where \[la]nnn\[ra] is a line number, and \[la]token\[ra] is a token near (usually
113 just after) the error location.
119 Pictures are described procedurally, as collections of objects
120 connected by motions. Normally, \fBpic\fP tries to string together
121 objects left-to-right in the sequence they are described, joining them
122 at visually natural points. Here is an example illustrating the
123 flow of data in \fBpic\fP processing:
128 box width 0.6 "\fIgpic\/\fP(1)"
130 box width 1.1 "\fIgtbl\/\fP(1) or \fIgeqn\/\fP(1)" "(optional)" dashed;
132 box width 0.6 "\fIgtroff\/\fP(1)";
136 .CE "1: Flow of \fBpic\fP data"
138 This was produced from the following \fBpic\fP program:
147 box width 0.6 "\efIpic\e/\efP(1)"
149 box width 1.1 "\efIgtbl\e/\efP(1) or \efIgeqn\e/\efP(1)" "(optional)" dashed;
151 box width 0.6 "\efIgtroff\e/\efP(1)";
159 This little program illustrates several \fBpic\fP basics. Firstly, we
160 see how to invoke three object types; ellipses, arrows, and boxes. We
161 see how to declare text lines to go within an object (and that text
162 can have font changes in it). We see how to change the line style of
163 an object from solid to dashed. And we see that a box can be made
164 wider than its default size to accommodate more text (we'll discuss
165 this facility in detail in the next section).
167 We also get to see \fBpic\fP's simple syntax. Statements are ended by
168 newlines or semicolons. String quotes are required around all text
169 arguments, whether or not they contain spaces. In general, the order
170 of command arguments and modifiers like \[lq]width 1.2\[rq] or
171 \[lq]dashed\[rq] doesn't matter, except that the order of text arguments
174 Here are all but one of the basic \fBpic\fP objects at their default sizes:
187 arc; down; move; "arc"
189 .CE "2: Basic \fBpic\fP objects"
191 The missing simple object type is a \fIspline\fP. There is also a way
192 to collect objects into \fIblock composites\fP which allows you to
193 treat the whole group as a single object (resembling a box) for many
194 purposes. We'll describe both of these later on.
196 The box, ellipse, circle, and block composite objects are \fIclosed\/\fR;
197 lines, arrows, arcs and splines are \fIopen\fP. This distinction
198 will often be important in explaining command modifiers.
200 Figure \n[H1]-2 was produced by the following \fBpic\fP program,
201 which introduces some more basic concepts:
216 arc; down; move; "arc"
222 The first thing to notice is the \fImove\fP command, which moves a
223 default distance (1/2 inch) in the current movement direction.
225 Secondly, see how we can also decorate lines and arrows with text.
226 The line and arrow commands each take two arguments here, specifying
227 text to go above and below the object. If you wonder why one argument
228 would not do, contemplate the output of \fBarrow "ow!"\fP:
233 .CE "3: Text centered on an arrow"
235 When a command takes one text string, \fBpic\fP tries to place it at
236 the object's geometric center. As you add more strings, \fBpic\fP
237 treats them as a vertical block to be centered. The program
244 line "1" "2" "3" "4";
245 line "1" "2" "3" "4" "5";
250 for example, gives you this:
257 line "1" "2" "3" "4";
258 line "1" "2" "3" "4" "5";
261 .CE "4: Effects of multiple text arguments"
263 The last line of Figure 3.2's program, `\fBarc; down; move;
264 "arc"\fP', describing the captioned arc, introduces several new ideas.
265 Firstly, we see how to change the direction in which objects are
266 joined. Had we written \fBarc; move; "arc"\fP,
267 omitting \fBdown\fP the caption would have been joined to the top
268 of the arc, like this:
273 .CE "5: Result of \fBarc; move; \"arc\"\fP"
275 This is because drawing an arc changes the default direction to the
276 one its exit end points at. To reinforce this point, consider:
281 .CE "6: Result of \fBarc cw; move; \"arc\"\fP"
283 All we've done differently here is specify \[lq]cw\[rq] for a clockwise arc
284 (\[lq]ccw\[rq] specifies counter-clockwise direction).
285 Observe how it changes the default direction to down, rather than up.
287 Another good way to see this via with the following program:
291 line; arc; arc cw; line
299 line; arc; arc cw; line;
301 .CE "7: Result of \fBline; arc; arc cw; line\fP"
303 Notice that we did not have to specify \[lq]up\[rq] for the second arc to be
304 joined to the end of the first.
306 Finally, observe that a string, alone, is treated as text to be
307 surrounded by an invisible box of a size either specified by width
308 and height attributes or by the defaults \fBtextwid\fR and
309 \fBtextht\fR. Both are initially zero (because we don't know the
316 Sizes are specified in inches. If you don't like inches, it's
317 possible to set a global style variable \fBscale\fP that changes the
318 unit. Setting \fBscale = 2.54\fP will effectively change the internal
319 unit to centimeters (all other size variable values will be scaled
323 Default Sizes of Objects
325 Here are the default sizes for \fBpic\fP objects:
327 center, tab(@), linesize(2);
336 box@0.75" wide by 0.5" high
338 ellipse@0.75" wide by 0.5" high
346 The simplest way to think about these defaults is that they make the
347 other basic objects fit snugly into a default-sized box.
350 Objects Do Not Stretch!
352 Text is rendered in the current font with normal troff line spacing.
353 Boxes, circles, and ellipses do \fInot\fP automatically resize to fit
354 enclosed text. Thus, if you say \fBbox "this text far too long for a
355 default box"\fP you'll get this:
358 box "this text is far too long for a default box"
360 .CE "1: Boxes do not automatically resize"
362 which is probably not the effect you want.
367 To change the box size, you can specify a box width with the \[lq]width\[rq]
371 box width 3 "this text is far too long for a default box"
373 .CE "2: Result of \fBbox width 3 \"text far too long\"\fP"
375 This modifier takes a dimension in inches. There is also a \[lq]height\[rq]
376 modifier that will change a box's height. The \fBwidth\fP keyword may
377 be abbreviated to \fBwid\fP; the \fBheight\fP keyword to \fBht\fP.
380 Resizing Other Object Types
382 To change the size of a circle, give it a \fBrad[ius]\fP or
383 \fBdiam[eter]\fP modifier; this changes the radius or diameter of the
384 circle, according to the numeric argument that follows.
387 {circle rad 0.1; move down 0.2 from last circle .s; "0.1"};
388 move; circle rad 0.2 "0.2"; move; circle rad 0.3 "0.3";
390 .CE "3: Circles with increasing radii"
392 The \fBmove\fP command can also take a dimension, which just tells
393 it how many inches to move in the current direction.
395 Ellipses are sized to fit in the rectangular box defined by their
396 axes, and can be resized with \fBwidth\fP and \fBheight\fP like boxes.
398 You can also change the radius of curvature of an arc with \fBrad[ius]\fP
399 (which specifies the radius of the circle of which the arc is a segment).
400 Larger values yield flatter arcs.
403 {arc rad 0.1; move down 0.3 from last arc .center; "0.1"};
405 {arc rad 0.2; move down 0.4 from last arc .center; "0.2"};
407 {arc rad 0.3; move down 0.5 from last arc .center; "0.3"};
409 .CE "4: \fBarc rad\fP with increasing radii"
411 Observe that because an arc is defined as a quarter circle, increasing
412 the radius also increases the size of the arc's bounding box.
417 In place of a dimension specification, you can use the keyword
418 \fBsame\fR. This gives the object the same size as the previous one
419 of its type. As an example, the program
424 box; box wid 1 ht 1; box same; box
433 box; box wid 1 ht 1; box same; box
435 .CE "5: The \fBsame\fP keyword"
439 Generalized Lines and Splines
444 It is possible to specify diagonal lines or arrows by adding multiple \fBup\fP,
445 \fBdown\fP, \fBleft\fP, and \fBright\fP modifiers to the line object.
446 Any of these can have a multiplier. To understand the effects, think
447 of the drawing area as being gridded with standard-sized boxes.
450 # Draw a demonstration up left arrow with grid box overlay
456 box wid 0.5 ht 0.5 dotted with .nw at last arrow .end;
457 for i = 2 to ($1 / 0.5) do {
458 box wid 0.5 ht 0.5 dotted with .sw at last box .se;
460 move down from last arrow .center;
462 if ( $1 == boxht ) then {
465 sprintf("\fBarrow up left %g\fP", $1)
469 move right 0.1 from last [] .e;
477 .CE "1: Diagonal arrows (dotted boxes show the implied 0.5-inch grid)"
480 Multi-Segment Line Objects
482 A \[lq]line\[rq] or \[lq]arrow\[rq] object may actually be a path
483 consisting of any number of segments of varying lengths and directions.
484 To describe a path, connect several line or arrow commands with the
488 define zigzag { $1 right 1 then down .5 left 1 then right 1 }
491 .CE "2: \fBline right 1 then down .5 left 1 then right 1\fP"
496 If you start a path with the \fBspline\fP keyword, the path vertices
497 are treated as control points for a spline curve fit.
501 move down 0.2 from last [] .s;
502 "The spline curve..."
503 move right from last [] .e;
506 spline from start of last line right 1 then down .5 left 1 then right 1;
507 "1" at last spline .start + (-0.1, 0);
508 "2" at last spline .start + (1.1, 0);
509 "3" at last spline .end + (-1.1, 0);
510 "4" at last spline .end + (0.1, 0);
512 move down 0.2 from last [] .s;
513 "...with tangents displayed"
516 .CE "3: \fBspline right 1 then down .5 left 1 then right 1\fP"
518 You can describe many natural-looking but irregular curves this
522 [spline right then up then left then down ->;]
523 move down 0.2 from last [] .s;
524 ["\fBspline right then up then left then down ->;\fP"]
525 move right 3 from last [] .se;
526 "\fBspline left then up right then down right ->;\fP"
528 [spline left then up right then down right ->;]
530 .CE "4: Two more spline examples"
532 Note the arrow decorations. Arrowheads can be applied naturally to
533 any path-based object, line or spline. We'll see how in the next
543 We've already seen that the modifier \fBdashed\fP can change the line
544 style of an object from solid to dashed. GNU \fBgpic\fP permits you to
545 dot or dash ellipses, circles, and arcs (and splines in \*[tx] mode
546 only); some versions of DWB may only permit dashing of lines and
547 boxes. It's possible to change the dash interval by specifying a
548 number after the modifier.
552 box dashed "default";
554 box dashed 0.05 "0.05";
556 box dashed 0.1 "0.1";
558 box dashed 0.15 "0.15";
560 box dashed 0.2 "0.2";
562 .CE "1: Dashed objects"
567 Another available qualifier is \fBdotted\fP. GNU \fBgpic\fP permits
568 you to dot or dash ellipses, circles, and arcs (and splines in \*[tx]
569 mode only); some versions of DWB may only permit dashing of lines and
570 boxes. It too can be suffixed with a number to specify the interval
574 box dotted "default";
576 box dotted 0.05 "0.05";
578 box dotted 0.1 "0.1";
580 box dotted 0.15 "0.15";
582 box dotted 0.2 "0.2";
584 .CE "2: Dotted objects"
589 It is also possible, in GNU \fBgpic\fP only, to modify a box so it has
593 box rad 0.05 "rad 0.05";
595 box rad 0.1 "rad 0.1";
597 box rad 0.15 "rad 0.15";
599 box rad 0.2 "rad 0.2";
601 box rad 0.25 "rad 0.25";
603 .CE "3: \fBbox rad\fP with increasing radius values"
605 Radius values higher than half the minimum box dimension are silently
606 truncated to that value.
611 Lines and arcs can be decorated as well. Any line or arc (and any
612 spline as well) can be decorated with arrowheads by adding one or more
618 .CE "4: Double-headed line made with \fBline <- ->\fP"
620 In fact, the \fBarrow\fP command is just shorthand for \fBline ->\fP. And
621 there is a double-head modifier <->, so the figure above could have been made
624 Arrowheads have a \fBwidth\fP attribute, the distance across the rear;
625 and a \fBheight\fP attribute, the length of the arrowhead along the shaft.
627 Arrowhead style is controlled by the style variable \fBarrowhead\fP.
628 The DWB and GNU versions interpret it differently. DWB defaults to
629 open arrowheads and an \fBarrowhead\fP value of\~2; the Kernighan
630 paper says a value of\~7 will make solid arrowheads. GNU \fBgpic\fP
631 defaults to solid arrowheads and an \fBarrowhead\fP value of\~1; a
632 value of\~0 will produce open arrowheads. Note that solid arrowheads are
633 always filled with the current outline color.
638 It's also possible to change the line thickness of an object (this is
639 a GNU extension, DWB \fBpic\fP doesn't support it).
640 The default thickness of the lines used to draw objects is controlled by the
643 This gives the thickness of lines in points.
644 A negative value means use the default thickness:
645 in \*[tx] output mode, this means use a thickness of 8 milliinches;
646 in \*[tx] output mode with the
648 option, this means use the line thickness specified by
650 lines; in troff output mode, this means use a thickness proportional
651 to the pointsize. A zero value means draw the thinnest possible line
652 supported by the output device. Initially it has a value of -1.
653 There is also a \fBthickness\fP attribute (which can be abbreviated to
654 \fBthick\fP). For example, \fBcircle thickness 1.5\fP would draw a
655 circle using a line with a thickness of 1.5 points. The thickness of
656 lines is not affected by the value of the
658 variable, nor by any width or height given in the
665 The modifier \fBinvis[ible]\fP makes an object entirely invisible. This
666 used to be useful for positioning text in an invisible object that is
667 properly joined to neighboring ones. Newer DWB versions and GNU
668 \fBpic\fP treat stand-alone text in exactly this way.
673 It is possible to fill boxes, circles, and ellipses. The
674 modifier \fBfill[ed]\fP accomplishes this. You can suffix it with a fill
675 value; the default is given by the stule variable \fBfillval\fP.
677 DWB \fBpic\fP and \fBgpic\fP have opposite conventions for fill values
678 and different defaults. DWB \fBfillval\fP defaults to 0.3 and smaller
679 values are darker; GNU \fBfillval\fP uses 0 for white and 1 for black.
682 circle fill; move; circle fill 0.4; move; circle fill 0.9;
684 .CE "5: \fBcircle fill; move; circle fill 0.4; move; circle fill 0.9;\fR"
686 GNU \fBgpic\fP makes some additional guarantees. A fill value greater
687 than 1 can also be used: this means fill with the shade of gray that
688 is currently being used for text and lines. Normally this will be
689 black, but output devices may provide a mechanism for changing this.
690 The invisible attribute does not affect the filling of objects. Any
691 text associated with a filled object will be added after the object
692 has been filled, so that the text will not be obscured by the filling.
694 The closed-object modifier \fBsolid\fP is equivalent to \fBfill\fP
695 with the darkest fill value (DWB \fBpic\fP had this capability but
696 mentioned it only in a reference section).
701 As a GNU extension, three additional modifiers are available to specify
702 colored objects. \fBoutline\fP sets the color of the outline, \fBshaded\fP
703 the fill color, and \fBcolor\fP sets both. All three keywords expect a
704 suffix specifying the color. Example:
707 box color "yellow"; arrow color "cyan"; circle shaded "green" outline "black";
709 .CE "6: \fBbox color ""yellow""; arrow color ""cyan""; \
710 circle shaded ""green"" outline ""black"";\fR"
712 Alternative spellings are \fBcolour\fP, \fBcolored\fP, \fBcoloured\fP,
715 Currently, color support is not available in \*[tx] mode. Predefined color
716 names for \fIgroff\/\fP(1) are in the device macro files, for example
717 \f(CWps.tmac\fP; additional colors can be defined with the \fB.defcolor\fP
718 request (see the manual page of GNU \fItroff\/\fP(1) for more details).
720 \fBpic\fP assumes that at the beginning of a picture both glyph and fill
721 color are set to the default value.
725 More About Text Placement
727 By default, text is centered at the geometric center of the object it is
728 associated with. The modifier \fBljust\fP causes the left end to be
729 at the specified point (which means that the text lies to the right of
730 the specified place!), the modifier \fBrjust\fP puts the right end at
731 the place. The modifiers \fBabove\fP and \fBbelow\fP center the text
732 one half line space in the given direction.
734 Text attributes can be combined:
737 [line up "ljust text" ljust;]
739 [line up "rjust text" rjust;]
741 [arrow 1 "ljust above" ljust above;]
743 [arrow 1 "rjust below" rjust below;]
745 .CE "1: Text attributes"
747 What actually happens is that \fIn\fP text strings are centered in a box
748 that is \fBtextwid\fP wide by \fBtextht\fP high. Both these variables
749 are initially zero (that is \fBpic\fR's way of not making assumptions
750 about \fI[tg]roff\/\fP(1)'s default point size).
752 In GNU \fBgpic\fR, objects can have an
755 This will only work when the postprocessor is
757 Any text associated with an object having the
759 attribute will be rotated about the center of the object
760 so that it is aligned in the direction from the start point
761 to the end point of the object.
762 Note that this attribute will have no effect for objects whose start and
763 end points are coincident.
767 More About Direction Changes
769 We've already seen how to change the direction in which objects are
770 composed from rightwards to downwards. Here are some more
771 illustrative examples:
776 "\fBright; box; arrow; circle; arrow; ellipse\fP";
778 [right; box; arrow; circle; arrow; ellipse;]
780 move down 0.3 from last [] .s;
782 "\fBleft; box; arrow; circle; arrow; ellipse\fP"
784 [left; box; arrow; circle; arrow; ellipse;]
786 # move down 0.3 from last [] .sw;
787 # To re-join this illustrations, delete everything from here down to
788 # the next #-comment, and uncomment the move line above
790 .CE "1: Effects of different motion directions (right and left)"
793 # To re-join this illustrations, delete everything down to here, then
794 # comment out the next `down' line.
795 # Don't forget to re-number the figures following!
798 "\fBdown; box; arrow; circle; arrow; ellipse;\fP"
800 box; arrow; circle; arrow; ellipse;
802 move right 2 from last [] .e;
804 up; box; arrow; circle; arrow; ellipse;
806 "\fBup; box; arrow; circle; arrow; ellipse;\fP"
809 .CE "2: Effects of different motion directions (up and down)"
811 Something that may appear surprising happens if you change directions
815 box; arrow; circle; down; arrow; ellipse
817 .CE "3: \fBbox; arrow; circle; down; arrow; ellipse\fP"
819 You might have expected that program to yield this:
822 box; arrow; circle; move to last circle .s; down; arrow; ellipse
824 .CE "4: More intuitive?"
826 But, in fact, to get Figure \*[SN]3 you have to do this:
834 move to last circle .s;
843 Why is this? Because the exit point for the current direction is
844 already set when you draw the object. The second arrow in Figure
845 \*[SN]2 dropped downwards from the circle's attachment point for an
846 object to be joined to the right.
848 The meaning of the command \fBmove to last circle .s\fP should be obvious.
849 In order to see how it generalizes, we'll need to go into detail on two
850 important topics; locations and object names.
856 The most natural way to name locations in \fBpic\fP is relative to
857 objects. In order to do this, you have to be able you have to be able
858 to name objects. The \fBpic\fP language has rich facilities for this
859 that try to emulate the syntax of English.
862 Naming Objects By Order Of Drawing
864 The simplest (and generally the most useful) way to name an object is
865 with a \fBlast\fP clause. It needs to be followed by an object type
866 name; \fBbox\fP, \fBcircle\fP, \fBellipse\fP, \fBline\fP, \fBarrow\fP,
867 \fBspline\fP, \fB""\fP, or \fB[]\fP (the last type refers to a \fIcomposite
868 object\fP which we'll discuss later). So, for example, the \fBlast
869 circle\fP clause in the program attached to Figure \*[SN]3 refers to the
872 More generally, objects of a given type are implicitly numbered
873 (starting from\~1). You can refer to (say) the third ellipse in the
874 current picture with \fB3rd ellipse\fP, or to the first box as \fB1st
875 box\fP, or to the fifth text string (which isn't an attribute to another
876 object) as \fB5th ""\fP.
878 Objects are also numbered backwards by type from the last one.
879 You can say \fB2nd last box\fP to get the second-to-last box, or
880 \fB3rd last ellipse\fP to get the third-to-last ellipse.
882 In places where \fIn\/\fBth\fR is allowed, \fB`\fIexpr\/\fB'th\fR is
883 also allowed. Note that
885 is a single token: no space is allowed between the
894 line from `i'th box.nw to `i+1'th box.se
901 Naming Objects With Labels
903 You can also specify an object by referring to a label. A label is a
904 word (which must begin with a capital letter) followed by a colon;
905 you declare it by placing it immediately before the object drawing command.
906 For example, the program
911 A: box "first" "object"
913 B: ellipse "second" "object"
921 declares labels \fBA\fP and \fBB\fP for its first and second objects.
922 Here's what that looks like:
925 A: box "first" "object"
927 B: ellipse "second" "object"
931 .CE "1: Example of label use"
932 The \fBat\fP statement in the fourth line uses the label \fBA\fP (the
933 behavior of \fBat\fP will be explained in the next section). We'll
934 see later on that labels are most useful for referring to block composite
937 Labels are not constants but variables (you can view colon as a sort
938 of assignment). You can say something like \fBA: A + (1,0);\fP
939 and the effect will be to reassign the label \fBA\fR to designate a
940 position one inch to the right of its old value.
946 The location of points can be described in many different ways. All these
947 forms are interchangeable as for as the \fBpic\fP language syntax is
948 concerned; where you can use one, any of the others that would make
949 semantic sense are allowed.
951 The special label \fBHere\fR always refers to the current position.
956 The simplest is absolute coordinates in inches; \fBpic\fP uses a
957 Cartesian system with (0,0) at the lower left corner of the virtual
958 drawing surface for each picture (that is, X increases to the right
959 and Y increases upwards). An absolute location may always be written in the
960 conventional form as two comma-separated numbers surrounded by
961 parentheses (and this is recommended for clarity). In contexts where
962 it creates no ambiguity, the pair of X and Y coordinates suffices
965 It is a good idea to avoid absolute coordinates, however. They tend
966 to make picture descriptions difficult to understand and modify.
967 Instead, there are quite a number of ways to specify locations
968 relative to \fBpic\fP objects and previous locations.
970 Another possibility of surprise is the fact that \fBpic\fP crops the
971 picture to the smallest bounding box before writing it out. For
972 example, if you have a picture consisting of a small box with its lower
973 left corner at (2,2) and another small box with its upper right corner
974 at (5,5), the width and height of the image are both 3\~units and
975 not~5. To get the origin at (0,0) included, simply add an invisible
976 object to the picture, positioning the object's left corner at (0,0).
979 Locations Relative to Objects
981 The symbol \fBHere\fP always refers to the position of the last object
982 drawn or the destination of the last \fBmove\fP.
984 Alone and unqualified, a \fBlast circle\fP or any other way of
985 specifying a closed-object or arc location refers as a position to the
986 geometric center of the object. Unqualified, the name of a line or
987 spline object refers to the position of the object start.
989 Also, \fBpic\fP objects have quite a few named locations
990 associated with them. One of these is the object center, which can be
991 indicated (redundantly) with the suffix \fB.center\fP (or just \fB.c\fP).
992 Thus, \fBlast circle \&.center\fP is equivalent to \fBlast
995 Locations Relative to Closed Objects
997 Every closed object (box, circle, ellipse, or block composite) also
998 has eight compass points associated with it;
1001 define dot {circle fill rad 0.02 at $1}
1005 dot(ME.c); "\fB .c\fP" at ME .c ljust;
1006 dot(ME.n); "\fB.n\fP" at ME .n above
1007 dot(ME.ne); "\fB .ne\fP" at ME .ne above
1008 dot(ME.e); "\fB .e\fP" at ME .e ljust
1009 dot(ME.se); "\fB .se\fP" at ME .se below
1010 dot(ME.s); "\fB.s\fP" at ME .s below
1011 dot(ME.sw); "\fB.sw \fP" at ME .sw below
1012 dot(ME.w); "\fB.w \fP" at ME .w rjust
1013 dot(ME.nw); "\fB.nw \fP" at ME .nw above
1015 compass(box wid 1.5 ht 1);
1016 move right from last [] .e;
1017 compass(circle diam 1);
1018 move right from last [] .e;
1019 compass(ellipse wid 1.5 ht 1);
1021 .CE "1: Compass points"
1023 these are the locations where eight compass rays from the geometric center
1024 would intersect the figure. So when we say \fBlast circle .s\fP we are
1025 referring to the south compass point of the last circle drawn. The
1026 explanation of Figure 7.3's program is now complete.
1028 (In case you dislike compass points, the names \fB.top\fP,
1029 \&\fB.bottom\fP, \fB.left\fP and \fB.right\fP are synonyms for \fB.n\fP,
1030 \&\fB.s\fP, \fB.e\fP, and \fB.w\fP respectively; they can even be
1031 abbreviated to \fB.t\fP, \fB.b\fP, \fB.l\fP and \fB.r\fP).
1033 The names \fBcenter\fP, \fBtop\fP, \fBbottom\fP, \fBleft\fP, \fBright\fP,
1034 \fBnorth\fP, \fBsouth\fP, \fBeast\fP, and \fBwest\fP can also be used
1035 (without the leading dot) in a prefix form marked by \fBof\fP; thus,
1036 \fBcenter of last circle\fP and \fBtop of 2nd last ellipse\fP are both
1037 valid object references. Finally, the names \fBleft\fP and \fBright\fP
1038 can be prefixed with \fBupper\fP and \fBlower\fP which both have the
1041 Arc objects also have compass point; they are the compass points of
1044 Locations Relative to Open Objects
1046 Every open object (line, arrow, arc, or spline) has three named
1047 points: \fB.start\fP, \fB.center\fP (or \fB.c\fP), and \fB.end\fP. They
1048 can also be used without leading dots in the \fBof\fP prefix form.
1049 The center of an arc is the center of its circle, but the center of
1050 a line, path, or spline is halfway between its endpoints.
1055 dot(ME.c); "\fB.center\fP" rjust at ME.center + (-0.1, 0.1)
1056 dot(ME.start); "\fB.start\fP" rjust at ME.start + (-0.1, 0.1)
1057 dot(ME.end); "\fB.end\fP" rjust at ME.end + (-0.1, 0.1)
1060 critical(line up right 1);
1061 move right 1 from last [] .e;
1062 critical(arc rad 0.5 cw);
1063 move down 0.5 from 2nd last [] .s;
1064 critical(line right 1 then down .5 left 1 then right 1);
1065 move right 1 from last [] .e;
1066 critical(spline right 1 then up right then left then left 1);
1068 .CE "2: Special points on open objects"
1072 Ways of Composing Positions
1074 Once you have two positions to work with, there are several ways to
1075 combine them to specify new positions.
1077 Vector Sums and Displacements
1079 Positions may be added or subtracted to yield a new position (to be
1080 more precise, you can only add a position and an expression pair; the
1081 latter must be on the right side of the addition or subtraction sign).
1082 The result is the conventional vector sum or difference of coordinates.
1083 For example, \fBlast box .ne + (0.1, 0)\fP is a valid position. This
1084 example illustrates a common use, to define a position slightly offset
1085 from a named one (say, for captioning purposes).
1087 Interpolation Between Positions
1089 A position may be interpolated between any two positions. The syntax
1090 is `\fIfraction\fP \fBof the way between\fP \fIposition1\fP \fBand\fP
1091 \fIposition2\fP'. For example, you can say \fB1/3 of the way between
1092 here and last ellipse .ne\fP. The fraction may be in
1093 numerator/denominator form or may be an ordinary number (values are
1094 \fInot\fP restricted to [0,1]). As an alternative to this verbose
1095 syntax, you can say `\fIfraction\fP \fB<\,\fP\fIposition1\fP \fB,\fP
1096 \fIposition2\/\fP\fB>\fP'; thus, the example could also be written as
1097 \fB1/3 <here, last ellipse>\fP.
1101 P: 1/3 of the way between last arrow .start and last arrow .end;
1102 dot(P); move right 0.1; "P";
1104 .CE "3: \fBP: 1/3 of the way between last arrow .start and last arrow .end\fP"
1106 This facility can be used, for example, to draw double connections.
1111 arrow right at 1/4 <A.e,A.ne>;
1112 arrow left at 1/4 <B.w,B.sw>;
1114 .CE "4: Doubled arrows"
1116 You can get Figure \n[H1]-4 from the following program:
1123 arrow right at 1/4 <A.e,A.ne>;
1124 arrow left at 1/4 <B.w,B.sw>;
1130 Note the use of the short form for interpolating points.
1132 Projections of Points
1134 Given two positions \fIp\fP and \fIq\fP, the position
1135 \fB(\,\fP\fIp\fP\fB,\fP \fIq\fP\fB)\fP has the X coordinate of \fIp\fP
1136 and the Y coordinate of \fIq\fP. This can be helpful in placing an
1137 object at one of the corners of the virtual box defined by two other
1141 box invis wid 2 height 1;
1142 dot(last box .ne); "\fB(B,A)\fP is here" ljust at last circle + (0.1, 0.1);
1143 dot(last box .se); "B" ljust at last circle + (0.1, -0.1)
1144 dot(last box .sw); "\fB(A,B)\fP is here" rjust at last circle + (-0.1, -0.1);
1145 dot(last box .nw); "A" ljust at last circle + (-0.1, 0.1)
1147 .CE "5: Using (\fIx\fP, \fIy\fP) composition"
1152 There are four ways to use locations; \fBat\fP, \fBfrom\fP, \fBto\fP,
1153 and \fBwith\fP. All three are object modifiers; that is, you use them
1154 as suffixes to a drawing command.
1156 The \fBat\fP modifier says to draw a closed object or arc with its
1157 center at the following location, or to draw a line/spline/arrow
1158 starting at the following location.
1160 The \fBto\fP modifier can be used alone to specify a move destination.
1161 The \fBfrom\fP modifier can be used alone in the same way as \fBat\fP.
1163 The \fBfrom\fP and \fBto\fP modifiers can be used with a \fBline\fR or
1164 \fBarc\fR command to specify start and end points of the object. In
1165 conjunction with named locations, this offers a very flexible
1166 mechanism for connecting objects. For example, the following program
1174 arc cw from 1/3 of the way \e
1175 between last box .n and last box .ne to last ellipse .n;
1187 arc cw from 1/3 of the way \
1188 between last box .n and last box .ne to last ellipse .n;
1190 .CE "6: A tricky connection specified with English-like syntax"
1192 The \fBwith\fP modifier allows you to identify a named attachment
1193 point of an object (or a position within the object) with another point.
1194 This is very useful for connecting objects in a natural way. For an
1195 example, consider these two programs:
1201 box wid 0.75 ht 0.75;
1203 move down 0.3 from last [] .s 0.1;
1204 "\fBbox wid 0.5 ht 0.5; box wid 0.75 ht 0.75\fP"
1206 move from last [].e 1.5
1210 box wid 0.75 ht 0.75 with .sw at last box .se;
1212 move down 0.3 from last [] .s 0.1;
1213 box invisible "\fBbox wid 0.5 ht 0.5;\fP" \
1214 "\fBbox wid 0.75 ht 0.75 with .sw at last box .se;\fP"
1217 .CE "7: Using the \fBwith\fP modifier for attachments"
1222 When drawing lines between circles that don't intersect them at a
1223 compass point, it is useful to be able to shorten a line by the radius
1224 of the circle at either or both ends. Consider the following program:
1230 circle "y" at 1st circle - (0.4, 0.6)
1231 circle "z" at 1st circle + (0.4, -0.6)
1232 arrow from 1st circle to 2nd circle chop
1233 arrow from 2nd circle to 3rd circle chop
1234 arrow from 3rd circle to 1st circle chop
1240 It yields the following:
1244 circle "y" at 1st circle - (0.4, 0.6)
1245 circle "z" at 1st circle + (0.4, -0.6)
1246 arrow from 1st circle to 2nd circle chop
1247 arrow from 2nd circle to 3rd circle chop
1248 arrow from 3rd circle to 1st circle chop
1250 .CE "8: The \fBchop\fR modifier"
1252 Notice that the \fBchop\fR attribute moves arrowheads rather than
1253 stepping on them. By default, the \fBchop\fR modifier shortens both
1254 ends of the line by \fBcirclerad\fR. By suffixing it with a number
1255 you can change the amount of chopping.
1257 If you say \fBline .\|.\|.\& chop \fIr1\fP chop \fIr2\fP\fR with \fIr1\fP
1258 and \fIr2\fP both numbers, you can vary the amount of chopping at both
1259 ends. You can use this in combination with trigonometric functions
1260 to write code that will deal with more complex intersections.
1266 There are two different ways to group objects in \fBpic\fP; \fIbrace
1267 grouping\fP and \fIblock composites\fP.
1272 The simpler method is simply to group a set of objects within curly
1273 bracket or brace characters. On exit from this grouping, the current
1274 position and direction are restored to their value when the opening
1275 brace was encountered.
1280 A block composite object is created a series of commands enclosed by
1281 square brackets. The composite can be treated for most purposes like
1282 a single closed object, with the size and shape of its bounding box.
1283 Here is an example. The program fragment
1289 line up 1 at last circle .n;
1290 line down 1 at last circle .s;
1291 line right 1 at last circle .e;
1292 line left 1 at last circle .w;
1293 box dashed with .nw at last circle .se + (0.2, -0.2);
1294 Caption: center of last box;
1300 yields the block in figure \n[H1]-1, which we show both with and
1301 without its attachment points. The block's location becomes the
1307 line up 1 at last circle .n;
1308 line down 1 at last circle .s;
1309 line right 1 at last circle .e;
1310 line left 1 at last circle .w;
1311 box dashed with .nw at last circle .se + (0.2, -0.2);
1312 Caption: center of last box;
1316 compass([junction()]);
1318 .CE "1: A sample composite object"
1320 To refer to one of the composite's attachment points, you can say
1321 (for example) \fBA .s\fP. For purposes of object naming, composites
1322 are a class. You could write \fBlast [] .s\fP as an equivalent
1323 reference, usable anywhere a location is needed. This construction is
1324 very important for putting together large, multi-part diagrams.
1326 Blocks are also a variable-scoping mechanism, like a \fIgroff\/\fP(1)
1327 environment. All variable assignments done inside a block are undone
1328 at the end of it. To get at values within a block, write a name of
1329 the block followed by a dot, followed by the label you
1330 want. For example, we could refer the the center of the box in the
1331 above composite as \fBlast [] .Caption\fP or \fBA.Caption\fP.
1333 This kind of reference to a label can be used in any way any other
1334 location can be. For example, if we added \fB"Hi!" at A.Caption\fP
1335 the result would look like this:
1341 .CE "2: Adding a caption using interior labeling"
1343 You can also use interior labels in either part of a \fBwith\fR
1344 modifier. This means that the example composite could be placed
1345 relative to its caption box by a command containing \fBwith A.Caption
1348 Note that both width and height of the block composite object are always
1355 box wid 0.75 ht 0.75
1357 move down 0.3 from last [].s 0.1
1358 "\fBbox wid -0.5 ht 0.5; box wid 0.75 ht 0.75\fP"
1360 move from last [].e 2
1363 [ box wid -0.5 ht 0.5 ]
1364 box wid 0.75 ht 0.75
1366 move down 0.3 from last [].s 0.1
1367 "\fB[box wid -0.5 ht 0.5]; box wid 0.75 ht 0.75\fP"
1370 .CE "3: Composite block objects always have positive width and height
1372 Blocks may be nested. This means you can use block attachment points
1373 to build up complex diagrams hierarchically, from the inside out.
1374 Note that \fBlast\fP and the other sequential naming mechanisms
1375 don't look inside blocks, so if you have a program that looks
1381 P: [box "foo"; ellipse "bar"];
1383 [box "baz"; ellipse "quxx"]
1386 arrow from 2nd last [];
1392 the arrow in the last line will be attached to object \fBP\fP, not
1395 In DWB \fBpic\fP, only references one level deep into enclosed blocks
1396 were permitted. GNU \fBgpic\fP removes this restriction.
1398 The combination of block variable scoping, assignability of labels and
1399 the macro facility that we'll describe later on can be used to
1400 simulate functions with local variables (just wrap the macro body in
1407 There are a number of global style variables in \fBpic\fR that can be used to
1408 change its overall behavior. We've mentioned several of them in
1409 previous sections. They're all described here. For each variable,
1410 the default is given.
1412 center, tab(@), linesize(2);
1416 Style Variable@Default@What It Does
1421 boxht@0.5@Default height of a box
1422 boxwid@0.75@Default width of a box
1423 lineht@0.5@Default length of vertical line
1424 linewid@0.75@Default length of horizontal line
1425 linethick@-1@Default line thickness
1426 arcrad @0.25@Default radius of an arc
1427 circlerad@0.25@Default radius of a circle
1428 ellipseht@0.5@Default height of an ellipse
1429 ellipsewid@0.75@Default width of an ellipse
1430 moveht@0.5@Default length of vertical move
1431 movewid@0.75@Default length of horizontal move
1432 textht@0@Default height of box enclosing a text object
1433 textwid@0@Default width of box enclosing a text object
1434 arrowht@0.1@Length of arrowhead along shaft
1435 arrowwid@0.05@Width of rear of arrowhead
1436 arrowhead@1@Enable/disable arrowhead filling
1437 dashwid@0.05@Interval for dashed lines
1438 maxpswid@11@Maximum width of picture
1439 maxpsht@8.5@Maximum height of picture
1440 scale@1@Unit scale factor
1441 fillval@0.5@Default fill value
1445 Any of these variables can be set with a simple assignment statement.
1449 [boxht=1; boxwid=0.3; movewid=0.2; box; move; box; move; box; move; box;]
1451 .CE "1: \fBboxht=1; boxwid=0.3; movewid=0.2; box; move; box; move; box; move; box;\fP"
1453 In GNU \fBpic\fR, setting the \fBscale\fR variable re-scales all
1454 size-related state variables so that their values remain equivalent in
1457 The command \fBreset\fP resets all style variables to their defaults.
1458 You can give it a list of variable names as arguments (optionally
1459 separated by commas), in which case it resets only those.
1461 State variables retain their values across pictures until reset.
1465 Expressions, Variables, and Assignment
1467 A number is a valid expression, of course (all numbers are stored
1468 internally as floating-point). Decimal-point notation is acceptable;
1469 in GNU \fBgpic\fR, scientific notation in C's `e' format (like
1470 \f(CW5e-2\fP) is accepted.
1472 Anywhere a number is expected, the language will also accept a
1473 variable. Variables may be the built-in style variable described in
1474 the last section, or new variables created by assignment.
1476 DWB \fBpic\fP supports only the ordinary assignment via \fB=\fP, which
1477 defines the variable (on the left side of the equal sign) in the current
1478 block if it is not already defined there, and then changes the value (on
1479 the right side) in the current block. The variable is not visible outside
1480 of the block. This is similar to the C\~programming language where a
1481 variable within a block shadows a variable with the same name outside of
1484 GNU \fBgpic\fP supports an alternate form of assignment using \fB:=\fP.
1485 The variable must already be defined, and the value will be assigned to
1486 that variable without creating a variable local to the current block.
1503 You can use the height, width, radius, and x and y coordinates of any
1504 object or corner in expressions. If \fBA\fP is an object label or name,
1505 all the following are valid:
1509 A.x # x coordinate of the center of A
1510 A.ne.y # y coordinate of the northeast corner of A
1511 A.wid # the width of A
1512 A.ht # and its height
1513 2nd last circle.rad # the radius of the 2nd last circle
1518 Note the second expression, showing how to extract a corner coordinate.
1520 Basic arithmetic resembling those of C operators are available; \fB+\fP,
1521 \fB*\fP, \fB-\fP, \fB/\fP, and \fB%\fP. So is \fB^\fP for exponentiation.
1522 Grouping is permitted in the usual way using parentheses. GNU \fBgpic\fP
1523 allows logical operators to appear in expressions; \fB!\&\fP (logical
1524 negation, not factorial), \fB&&\fP, \fB|\||\fP, \fB==\fP, \fB!=\fP,
1525 \fB>=\fP, \fB<=\fP, \fB<\fP, \fB>\fP.
1527 Various built-in functions are supported: \fBsin(\fIx\fB)\fR,
1528 \fBcos(\fIx\fB)\fR, \fBlog(\fIx\fB)\fR, \fBexp(\fIx\fB)\fR,
1529 \fBsqrt(\fIx\fB)\fR, \fBmax(\fIx\fB,\fIy\fB)\fR,
1530 \fBatan2(\fIx\fB,\fIy\fB)\fR, \fBmin(\fIx\fB,\fIy\fB)\fR,
1531 \fBint(\fIx\fB)\fR, \fBrand()\fP, and \fBsrand()\fP.
1532 Both \fBexp\fP and \fBlog\fP are
1533 base\~10; \fBint\fP does integer truncation; \fBrand()\fP returns a
1534 random number in [0-1), and \fBsrand()\fP sets the seed for
1535 a new sequence of pseudo-random numbers to be returned by \fBrand()\fP
1536 (\fBsrand()\fP is a GNU extension).
1538 GNU \fBgpic\fP also documents a one-argument form or rand,
1539 \fBrand(\fIx\fB)\fR, which returns a random number between 1 and
1540 \fIx\fP, but this is deprecated and may be removed in a future
1543 The function \fBsprintf()\fP behaves like a C \fIsprintf\/\fP(3)
1544 function that only takes %, %e, %f, and %g format strings.
1550 You can define macros in \fBpic\fP. This is useful for diagrams with
1551 repetitive parts. In conjunction with the scope rules for block
1552 composites, it effectively gives you the ability to write functions.
1557 \fBdefine\fP \fIname\fP \fB{\fP \fIreplacement text \fB}\fP
1561 This defines \fIname\fR as a macro to be replaced by the replacement
1562 text (not including the braces). The macro may be called as
1565 \fIname\fB(\fIarg1, arg2, \|.\|.\|.\& argn\fB)\fR
1569 The arguments (if any) will be substituted for tokens \fB$1\fP, \fB$2\fP
1570 \&.\|.\|.\& \fB$n\fP
1571 appearing in the replacement text.
1573 As an example of macro use, consider this:
1580 # Plot a single jumper in a box, $1 is the on-off state.
1583 Outer: box invis wid 0.45 ht 1;
1585 # Count on end ] to reset these
1586 boxwid = Outer.wid * shrinkfactor / 2;
1587 boxht = Outer.ht * shrinkfactor / 2;
1589 box fill (!$1) with .s at center of Outer;
1590 box fill ($1) with .n at center of Outer;
1593 # Plot a block of six jumpers.
1594 define jumperblock {
1602 jwidth = last [].Outer.wid;
1603 jheight = last [].Outer.ht;
1605 box with .nw at 6th last [].nw wid 6*jwidth ht jheight;
1607 # Use {} to avoid changing position from last box draw.
1608 # This is necessary so move in any direction will work as expected
1609 {"Jumpers in state $1$2$3$4$5$6" at last box .s + (0,-0.2);}
1612 # Sample macro invocations.
1613 jumperblock(1,1,0,0,1,0);
1615 jumperblock(1,0,1,0,1,1);
1623 It yields the following:
1626 # Plot a single jumper in a box, $1 is the on-off state.
1629 Outer: box invis wid 0.45 ht 1;
1631 # Count on end ] to reset these
1632 boxwid = Outer.wid * shrinkfactor / 2;
1633 boxht = Outer.ht * shrinkfactor / 2;
1635 box fill (!$1) with .s at center of Outer;
1636 box fill ($1) with .n at center of Outer;
1639 # Plot a block of six jumpers
1640 define jumperblock {
1648 jwidth = last [].Outer.wid;
1649 jheight = last [].Outer.ht;
1651 box with .nw at 6th last [].nw wid 6*jwidth ht jheight;
1653 # Use {} to avoid changing position from last box draw.
1654 # This is necessary so move in any direction will work as expected
1655 {"Jumpers in state $1$2$3$4$5$6" at last box .s + (0,-0.2);}
1658 # Sample macro invocations
1659 jumperblock(1,1,0,0,1,0);
1661 jumperblock(1,0,1,0,1,1);
1663 .CE "1: Sample use of a macro"
1665 This macro example illustrates how you can combine [], brace grouping,
1666 and variable assignment to write true functions.
1668 One detail the example above does not illustrate is the fact that
1669 macro argument parsing is not token-oriented. If you call
1670 \fBjumper(\ 1\ )\fP, the value of $1 will be \fB"\ 1\ "\fP. You could
1671 even call \fBjumper(big\ string)\fP to give $1 the value
1672 \fB"big\ string"\fP.
1674 If you want to pass in a coordinate pair, you can avoid getting
1675 tripped up by the comma by wrapping the pair in parentheses.
1677 Macros persist through pictures. To undefine a macro, say \fBundef\fP
1678 \fIname\fR; for example,
1680 \f(CWundef jumper\fP
1681 \f(CWundef jumperblock\fP
1684 would undefine the two macros in the jumper block example.
1688 Import/Export Commands
1690 Commands that import or export data between \fBpic\fR and its
1691 environment are described here.
1694 File and Table Insertion
1698 \f(CWcopy\fP \fIfilename\fR
1701 inserts the contents of \fIfilename\fR in the \fBpic\fP input stream.
1702 Any \fB.PS\fP/\fB.PE\fP pair in the file will be ignored. You
1703 can use this to include pre-generated images.
1705 A variant of this statement replicates the \fBcopy thru\fP feature of
1706 \fIgrap\fP(1). The call
1708 \f(CWcopy\fP \fIfilename\fR \f(CWthru\fP \fImacro\fP
1711 calls \fImacro\fP (which may be either a name or replacement text)
1712 on the arguments obtained by breaking each line of the file into
1713 blank-separated fields. The macro may have up to 9\~arguments. The
1714 replacement text may be delimited by braces or by a pair of instances
1715 of any character not appearing in the rest of the text.
1719 \f(CWcopy\fP \f(CWthru\fP \fImacro\fP
1722 omitting the filename, lines to be parsed are taken from the input
1723 source up to the next \fB.PE\fP.
1725 In either of the last two \fBcopy\fP commands, GNU \fBgpic\fP permits a
1726 trailing `\fBuntil\fP \fIword\/\fP' clause to be added which terminates
1727 the copy when the first word matches the argument (the default
1728 behavior is therefore equivalent to \fBuntil .PE\fP).
1730 Accordingly, the command
1737 copy thru % circle at ($1,$2) % until "END"
1769 The command \fBprint\fR accepts any number of arguments, concatenates
1770 their output forms, and writes the result to standard error. Each
1771 argument must be an expression, a position, or a text string.
1774 Escape to Post-Processor
1778 \fBcommand\fR \fIarg\fR\|.\|.\|.
1781 \fBpic\fP concatenates the arguments and pass them through as a line
1782 to troff or \*[tx]. Each
1784 must be an expression, a position, or text.
1785 This has a similar effect to a line beginning with
1789 but allows the values of variables to be passed through.
1792 Executing Shell Commands
1796 \f(CWsh\fP \f(CW{\fP \fIanything.\|.\|.\fP \f(CW}\fP
1799 macro-expands the text in braces, then executes it as a shell command.
1800 This could be used to generate images or data tables for later
1801 inclusion. The delimiters shown as {} here may also be two copies of
1802 any one character not present in the shell command text. In either
1803 case, the body may contain balanced {} pairs. Strings in the body
1804 may contain balanced or unbalanced braces in any case.
1808 Control-flow constructs
1810 The \fBpic\fP language provides conditionals and looping. For
1816 for i = 0 to 2 * pi by 0.1 do {
1818 "." at (i/2, sin(i)/2);
1819 ":" at (i/2, cos(i)/2);
1829 for i = 0 to 2 * pi by 0.1 do {
1831 "." at (i/2, sin(i)/2);
1832 ":" at (i/2, cos(i)/2);
1835 .CE "1: Plotting with a \fBfor\fP loop"
1837 The syntax of the \fBfor\fP statement is:
1839 \fBfor\fR \fIvariable\fR \fB=\fR \fIexpr1\/\fR \fBto\fR \fIexpr2\/\fR \
1840 [\fBby\fR [\fB*\fR]\fIexpr3\/\fR] \fBdo\fR \fIX\fR \fIbody\fR \fIX\fR
1842 The semantics are as follows: Set
1847 is less than or equal to
1857 is not given, increment
1866 will instead be multiplied by
1869 can be any character not occurring in
1870 \fIbody\fR; or the two \fIX\/\fPs may be paired braces (as in the
1873 The syntax of the \fBif\fP statement is as follows:
1875 \fBif\fR \fIexpr\fR \fBthen\fR \fIX\fR \fIif-true\fR \fIX\fR \
1876 [\fBelse\fR \fIY\fR \fIif-false\fR \fIY\/\fR]
1878 Its semantics are as follows: Evaluate
1880 if it is non-zero then do
1885 can be any character not occurring in
1888 can be any character not occurring in
1891 Eithe or both of the
1895 pairs may instead be balanced pairs of
1896 braces ({ and\~}) as in the \fBsh\fR command. In either case, the
1897 \fIif-true\fR may contain balanced pairs of braces. None of these
1898 delimiters will be seen inside strings.
1900 All the usual relational operators my be used in conditional expressions;
1901 \fB!\&\fP (logical negation, not factorial), \fB&&\fP, \fB|\||\fP, \fB==\fP,
1902 \fB!=\fP, \fB>=\fP, \fB<=\fP, \fB<\fP, \fB>\fP.
1904 String comparison is also supported using \fB==\fP and \fB!=\fP. String
1905 comparisons may need to be parenthesized to avoid syntactic
1910 Interface To [gt]roff
1912 The output of \fBpic\fP is \fB[gt]roff\fP drawing commands. The GNU
1913 \fIgpic\/\fP(1) command warns that it relies on drawing extensions
1914 present in \fIgroff\/\fP(1) that are not present in \fItroff\/\fP(1).
1919 The DWB \fIpic\/\fP(1) program will accept one or two arguments to
1920 \&\fB.PS\fP, which is interpreted as a width and height in inches to
1921 which the results of \fIpic\/\fP(1) should be scaled (width and height
1922 scale independently). If there is only one argument, it is
1923 interpreted as a width to scale the picture to, and height will be
1924 scaled by the same proportion.
1926 GNU \fBgpic\fP is less general; it will accept a single width to scale
1927 to, or a zero width and a maximum height to scale to. With
1928 two non-zero arguments, it will scale to the maximum height.
1931 How Scaling is Handled
1933 When \fBpic\fP processes a picture description on input, it passes
1934 \fB.PS\fP and \fB.PE\fP through to the postprocessor. The \fB.PS\fP
1935 gets decorated with two numeric arguments which are the X and
1936 Y\~dimensions of the picture in inches. The post-processor can use
1937 these to reserve space for the picture and center it.
1939 The GNU incarnation of the \fBms\fP macro package, for example, includes
1940 the following definitions:
1949 \&.ie \e\en[.$]<2 .@error bad arguments to PS (not preprocessed with pic?)
1951 \&. ds@need (u;\e\e$1)+1v
1952 \&. in +(u;\e\en[.l]-\e\en[.i]-\e\e$2/2>?0)
1957 \&.sp \e\en[DD]u+.5m
1965 Equivalent definition will be supplied by GNU \fIpic\/\fP(1) if you use
1966 the \-mpic option; this should make it usable with macro pages other
1969 If \fB.PF\fP is used instead of \fB.PE\fP, the \fBtroff\fP position is
1970 restored to what it was at the picture start (Kernighan notes that
1971 the\~F stands for \[lq]flyback\[rq]).
1975 \&\fB.PS <\,\fP\fIfile\fP
1978 causes the contents of \fIfile\fP to replace the \fB.PS\fP line. This
1979 feature is deprecated; use `\fBcopy\fP \fIfile\fR' instead).
1982 PIC and [gt]roff commands
1984 By default, input lines that begin with a period are passed to the
1985 postprocessor, embedded at the corresponding point in the output.
1986 Messing with horizontal or vertical spacing is an obvious recipe for
1987 bugs, but point size and font changes will usually be safe.
1989 Point sizes and font changes are also safe within text strings, as
1990 long as they are undone before the end of string.
1992 The state of \fB[gt]roff\fP's fill mode is preserved across pictures.
1997 The Kernighan paper notes that there is a subtle problem with
1998 complicated equations inside \fBpic\fR pictures; they come out wrong if
1999 \fIeqn\/\fP(1) has to leave extra vertical space for the equation.
2000 If your equation involves more than subscripts and superscripts, you
2001 must add to the beginning of each equation the extra information
2002 \fBspace\~0\fP. He gives the following example:
2007 box "$space 0 {H( omega )} over {1 - H( omega )}$"
2018 box "@space 0 {H( omega )} over {1 - H( omega )}@"
2021 .CE "1: Equations within pictures"
2024 Absolute Positioning of Pictures
2026 A \fBpic\fP picture is positioned vertically by troff at the current
2027 position. The topmost position possible on a page is not the paper edge
2028 but a position which is one baseline lower so that the first row of glyphs
2029 is visible. To make a picture really start at the paper edge you have
2030 to make the baseline-to-baseline distance zero, this is, you must set the
2031 vertical spacing to\~0 (using \fB.vs\fP) before starting the picture.
2038 \*[tx] mode is enabled by the
2041 In \*[tx] mode, pic will define a vbox called
2043 for each picture; the name can be changed with the pseudo-variable
2045 (which is actually a specially parsed command).
2046 You must yourself print that vbox using, for example, the command
2050 \ecenterline{\ebox\egraph}
2053 Actually, since the vbox has a height of zero (it is defined with \evtop)
2054 this will produce slightly more vertical space above the picture than
2059 \ecenterline{\eraise 1em\ebox\egraph}
2064 To make the vbox having a positive height and a depth of zero (as used
2065 e.g.\& by \*(lx's \f(CW\%graphics.sty\fP), define the following macro in
2071 \evbox{\eunvbox\ecsname #1\eendcsname\ekern 0pt}}
2076 Now you can simply say
2078 instead of \ebox\egraph.
2080 You must use a \*[tx] driver that supports the
2082 specials, version\~2.
2084 Lines beginning with
2086 are passed through transparently; a
2088 is added to the end of the line to avoid unwanted spaces.
2089 You can safely use this feature to change fonts or to
2090 change the value of \fB\ebaselineskip\fP.
2091 Anything else may well produce undesirable results; use at your own risk.
2092 Lines beginning with a period are not given any special treatment.
2094 The \*[tx] mode of \fIpic\/\fP(1) will \fInot\fP translate \fBtroff\fP
2095 font and size changes included in text strings!
2097 Here an example how to use \fBfigname\fP.
2111 \ecenterline{\ebox\efoo \ehss \ebox\ebar}
2116 Use this feature sparsingly and only if really needed:
2117 A different name means a new box register in \*[tx], and the maximum number
2118 of box registers is only 256.
2119 Also be careful not to use a predefined \*[tx] or \*[lx] macro name as
2120 an argument to \fBfigname\fP since this inevitably causes an error.
2126 GNU \fIgpic\/\fP(1) has a command
2128 \fBplot\fR \fIexpr\fR [\fB"\fItext\fB"\fR]
2130 This is a text object which is constructed by using
2132 as a format string for sprintf
2137 is omitted a format string of \fB"%g"\fP is used.
2138 Attributes can be specified in the same way as for a normal text
2140 Be very careful that you specify an appropriate format string;
2141 \fBpic\fP does only very limited checking of the string.
2142 This is deprecated in favour of
2147 Some Larger Examples
2149 Here are a few larger examples, with complete source code.
2150 One of our earlier examples is generated in an instructive way using a
2158 # Draw a demonstration up left arrow with grid box overlay
2164 box wid 0.5 ht 0.5 dotted with .nw at last arrow .end;
2165 for i = 2 to ($1 / 0.5) do
2167 box wid 0.5 ht 0.5 dotted with .sw at last box .se;
2169 move down from last arrow .center;
2171 if ( $1 == boxht ) \e
2172 then { "\efBline up left\efP" } \e
2173 else { sprintf("\efBarrow up left %g\efP", $1) };
2176 move right 0.1 from last [] .e;
2191 # Draw a demonstration up left arrow with grid box overlay
2197 box wid 0.5 ht 0.5 dotted with .nw at last arrow .end;
2198 for i = 2 to ($1 / 0.5) do
2200 box wid 0.5 ht 0.5 dotted with .sw at last box .se;
2202 move down from last arrow .center;
2204 if ( $1 == boxht ) \
2205 then { "\fBline up left\fP" } \
2206 else { sprintf("\fBarrow up left %g\fP", $1) };
2209 move right 0.1 from last [] .e;
2217 .CE "1: Diagonal arrows (dotted boxes show the implied 0.5-inch grid)"
2219 Here's an example concocted to demonstrate layout of a large,
2220 multiple-part pattern:
2227 define filter {box ht 0.25 rad 0.125}
2231 box "\efBms\efR" "sources";
2233 box "\efBHTML\efR" "sources";
2235 box "\efBlinuxdoc-sgml\efP" "sources" wid 1.5;
2237 box "\efBTexinfo\efP" "sources";
2239 line down from 1st box .s lineht;
2241 line down from 2nd box .s; filter "\efBhtml2ms\efP";
2243 line down from 3rd box .s; filter "\efBformat\efP";
2245 line down from 4th box .s; filter "\efBtexi2roff\efP";
2248 move down 1 from last [] .s;
2249 Anchor: box wid 1 ht 0.75 "\efBms\efR" "intermediate" "form";
2250 arrow from Top.A.end to Anchor.nw;
2251 arrow from Top.B.end to 1/3 of the way between Anchor.nw and Anchor.ne;
2252 arrow from Top.C.end to 2/3 of the way between Anchor.nw and Anchor.ne;
2253 arrow from Top.D.end to Anchor.ne
2257 line down left then down ->;
2258 filter "\efBpic\efP";
2260 filter "\efBeqn\efP";
2262 filter "\efBtbl\efP";
2264 filter "\efBgroff\efP";
2270 line down right then down ->;
2271 A: filter dotted "\efBpic2img\efP";
2273 B: filter dotted "\efBeqn2html\efP";
2275 C: filter dotted "\efBtbl2html\efP";
2277 filter "\efBms2html\efP";
2281 # Nonexistence caption
2282 box dashed wid 1 at B + (2,0) "These tools" "don't yet exist";
2283 line chop 0 chop 0.1 dashed from last box .nw to A.e ->;
2284 line chop 0 chop 0.1 dashed from last box .w to B.e ->;
2285 line chop 0 chop 0.1 dashed from last box .sw to C.e ->;
2295 define filter {box ht 0.25 rad 0.125}
2299 box "\fBms\fR" "sources";
2301 box "\fBHTML\fR" "sources";
2303 box "\fBlinuxdoc-sgml\fP" "sources" wid 1.5;
2305 box "\fBTexinfo\fP" "sources";
2307 line down from 1st box .s lineht;
2309 line down from 2nd box .s; filter "\fBhtml2ms\fP";
2311 line down from 3rd box .s; filter "\fBformat\fP";
2313 line down from 4th box .s; filter "\fBtexi2roff\fP";
2316 move down 1 from last [] .s;
2317 Anchor: box wid 1 ht 0.75 "\fBms\fR" "intermediate" "form";
2318 arrow from Top.A.end to Anchor.nw;
2319 arrow from Top.B.end to 1/3 of the way between Anchor.nw and Anchor.ne;
2320 arrow from Top.C.end to 2/3 of the way between Anchor.nw and Anchor.ne;
2321 arrow from Top.D.end to Anchor.ne
2325 line down left then down ->;
2332 filter "\fBgroff\fP";
2338 line down right then down ->;
2339 A: filter dotted "\fBpic2img\fP";
2341 B: filter dotted "\fBeqn2html\fP";
2343 C: filter dotted "\fBtbl2html\fP";
2345 filter "\fBms2html\fP";
2349 # Nonexistence caption
2350 box dashed wid 1 at B + (2,0) "These tools" "don't yet exist";
2351 line chop 0 chop 0.1 dashed from last box .nw to A.e ->;
2352 line chop 0 chop 0.1 dashed from last box .w to B.e ->;
2353 line chop 0 chop 0.1 dashed from last box .sw to C.e ->;
2356 .CE "2: Hypothetical production flow for dual-mode publishing"
2364 This is an annotated grammar of \fBpic\fP.
2369 In general, \fBpic\fP is a free-format, token-oriented language that
2370 ignores whitespace outside strings. But certain lines and contructs
2371 are specially interpreted at the lexical level:
2373 A comment begins with \fB#\fP and continues to \fB\en\fP (comments may
2374 also follow text in a line). A line beginning with a period or
2375 backslash may be interpreted as text to be passed through to the
2376 post-processor, depending on command-line options. An end-of-line
2377 backslash is interpreted as a request to continue the line; the
2378 backslash and following newline are ignored.
2381 Here are the grammar terminals:
2384 .IP \s[-1]NUMBER\s[0]
2385 A floating point numeric constant. May contain a decimal point or be
2386 expressed in scientific notation in the style of \fIprintf\/\fP(3)'s %e
2387 escape. A trailing `i' or `I' (indicating the unit `inch') is ignored.
2389 A string enclosed in double quotes. A double quote within \s[-1]TEXT\s[0]
2390 must be preceded by a backslash. Instead of \s[-1]TEXT\s[0] you can use
2393 sprintf ( TEXT [, <expr> ...] )
2397 except after the `until' and `last' keywords, and after all ordinal
2398 keywords (`th' and friends).
2399 .IP \s[-1]VARIABLE\s[0]
2400 A string starting with a character from the set [a-z], optionally
2401 followed by one or more characters of the set [a-zA-Z0-9_].
2402 (Values of variables are preserved across pictures.)
2403 .IP \s[-1]LABEL\s[0]
2404 A string starting with a character from the set [A-Z], optionally
2405 followed by one or more characters of the set [a-zA-Z0-9_].
2406 .IP \s[-1]COMMAND-LINE\s[0]
2407 A line starting with a command character (`.' in groff mode, `\e' in
2409 .IP \s[-1]BALANCED-TEXT\s[0]
2410 A string either enclosed by `{' and `}' or with \fIX\fP and \fIX\fP,
2411 where \fIX\fP doesn't occur in the string.
2412 .IP \s[-1]BALANCED-BODY\s[0]
2413 Delimiters as in \s[-1]BALANCED-TEXT\s[0]; the body will be interpreted as
2414 `\fB\[la]command\[ra].\|.\|.\fP'.
2415 .IP \s[-1]FILENAME\s[0]
2416 The name of a file. This has the same semantics as \s[-1]TEXT\s[0].
2417 .IP \s[-1]MACRONAME\s[0]
2418 Either \s[-1]VARIABLE\s[0] or \s[-1]LABEL\s[0].
2424 Tokens not enclosed in \[la]\|\[ra] are literals, except:
2426 \fB\en\fP is a newline.
2428 Three dots is a suffix meaning `replace with 0 or more repetitions
2429 of the preceding element(s).
2431 An enclosure in square brackets has its usual meaning of `this clause is
2434 Square-bracket-enclosed portions within tokens are optional. Thus,
2435 `h\^[eigh]\^t' matches either `height' or `ht'.
2437 If one of these special tokens has to be referred to literally, it is
2438 surrounded with single quotes.
2440 The top-level \fBpic\fP object is a picture.
2444 .PS [NUMBER [NUMBER]]\en
2450 The arguments, if present, represent the width and height of the picture,
2451 causing \fBpic\fR to attempt to scale it to the given dimensions in
2452 inches. In no case, however, will the X and Y\~dimensions of the
2453 picture exceed the values of the style variables \fBmaxpswid\fP and
2454 \fBmaxpsheight\fP (which default to the normal 8.5\^i by 11\^i page size).
2456 If the ending `.PE' is replaced by `.PF', the page vertical position is
2457 restored to its value at the time `.PS' was encountered. Another
2458 alternate form of invocation is `.PS\ <\s[-1]FILENAME\s[0]', which
2459 replaces the `.PS' line with a file to be interpreted by \fBpic\fR (but
2460 this feature is deprecated).
2462 The `.PS', `.PE', and `.PF' macros to perform centering and scaling are
2463 normally supplied by the post-processor.
2465 In the following, either `|' or a new line starts an alternative.
2476 <primitive> [<attribute>]
2477 LABEL : [;] <command>
2478 LABEL : [;] <command> [<position>]
2480 VARIABLE [:] = <any-expr>
2482 up | down | left | right
2484 command <print-arg> ...
2485 print <print-arg> ...
2488 copy [FILENAME] thru MACRONAME [until TEXT]
2489 copy [FILENAME] thru BALANCED-BODY [until TEXT]
2490 for VARIABLE = <expr> to <expr> [by [*] <expr>] do BALANCED-BODY
2491 if <any-expr> then BALANCED-BODY [else BALANCED-BODY]
2492 reset [VARIABLE [[,] VARIABLE ...]]
2504 The current position and direction are saved on entry to a `{\ .\|.\|.\ }'
2505 construction and restored on exit from it.
2507 Note that in `if' constructions, newlines can only occur in
2508 \s[-1]BALANCED-BODY\s[0]. This means that
2518 will fail. You have to use the braces on the same line as the keywords:
2529 This restriction doesn't hold for the body after the `do' in a `for'
2532 At the beginning of each picture, `figname' is reset to the vbox name
2533 `graph'; this command has only a meaning in \*[tx] mode. While the grammar
2534 rules allow digits and the underscore in the value of `figname', \*[tx]
2535 normally accepts uppercase and lowercase letters only as box names
2536 (you have to use `\ecsname' if you really need to circumvent this
2543 <any-expr> <logical-op> <any-expr>
2561 Logical operators are handled specially by \fBpic\fP since they can
2562 deal with text strings also. \fBpic\fP uses \%\fIstrcmp\/\fP(3) to test
2563 for equality of strings; an empty string is considered as `false' for
2568 box \fR# closed object \[em] rectangle\fP
2569 circle \fR# closed object \[em] circle\fP
2570 ellipse \fR# closed object \[em] ellipse\fP
2571 arc \fR# open object \[em] quarter-circle\fP
2572 line \fR# open object \[em] line\fP
2573 arrow \fR# open object \[em] line with arrowhead\fP
2574 spline \fR# open object \[em] spline curve\fP
2576 TEXT TEXT ... \fR# text within invisible box\fP
2577 plot <expr> TEXT \fR# formatted text\fP
2578 '[' <command> ... ']'
2582 Drawn objects within `[\ .\|.\|.\ ]' are treated as a single composite
2583 object with a rectangular shape (that of the bounding box of all the
2584 elements). Variable and label assignments within a block are local to
2585 the block. Current direction of motion is restored to the value at start
2586 of block upon exit. Position is \fInot\fR restored (unlike `{\ }');
2587 instead, the current position becomes the exit position for the current
2588 direction on the block's bounding box.
2592 h[eigh]t <expr> \fR# set height of closed figure \fP
2593 wid[th] <expr> \fR# set width of closed figure \fP
2594 rad[ius] <expr> \fR# set radius of circle/arc \fP
2595 diam[eter] <expr> \fR# set diameter of circle/arc \fP
2596 up [<expr>] \fR# move up \fP
2597 down [<expr>] \fR# move down \fP
2598 left [<expr>] \fR# move left \fP
2599 right [<expr>] \fR# move right \fP
2600 from <position> \fR# set from position of open figure\fP
2601 to <position> \fR# set to position of open figure\fP
2602 at <position> \fR# set center of open figure\fP
2603 with <path> \fR# fix corner/named point at specified location\fP
2604 with <position> \fR# fix position of object at specified location\fP
2605 by <expr-pair> \fR# set object's attachment point\fP
2606 then \fR# sequential segment composition\fP
2607 dotted [<expr>] \fR# set dotted line style\fP
2608 dashed [<expr>] \fR# set dashed line style\fP
2609 thick[ness] <expr> \fR# set thickness of lines\fP
2610 chop [<expr>] \fR# chop end(s) of segment\fP
2611 '->' | '<-' | '<->' \fR# decorate with arrows\fP
2612 invis[ible] \fR# make primitive invisible\fP
2613 solid \fR# make closed figure solid\fP
2614 fill[ed] [<expr>] \fR# set fill density for figure\fP
2615 colo[u]r[ed] TEXT \fR# set fill and outline color for figure\fP
2616 outline[d] TEXT \fR# set outline color for figure\fP
2617 shaded TEXT \fR# set fill color for figure\fP
2618 same \fR# copy size of previous object\fP
2619 cw | ccw \fR# set orientation of curves\fP
2620 ljust | rjust \fR# adjust text horizontally\fP
2621 above | below \fR# adjust text vertically\fP
2622 aligned \fR# align parallel to object\fP
2623 TEXT TEXT ... \fR# text within object\fP
2624 <expr> \fR# motion in the current direction\fR
2628 Missing attributes are supplied from defaults; inappropriate ones are
2629 silently ignored. For lines, splines, and arcs, height and width
2630 refer to arrowhead size.
2632 The `at' primitive sets the center of the current object. The
2633 `with' attribute fixes the specified feature of the given object
2634 to a specified location. (Note that `with' is incorrectly described
2635 in the Kernighan paper.)
2637 The `by' primitive is not documented in the tutorial portion of
2638 the Kernighan paper, and should probably be considered unreliable.
2640 The primitive `arrow' is a synonym for `line\ ->'.
2642 Text is normally an attribute of some object, in which case successive
2643 strings are vertically stacked and centered on the object's center by
2644 default. Standalone text is treated as though placed in an invisible
2647 A text item consists of a string or sprintf-expression, optionally
2648 followed by positioning information. Text (or strings specified with
2649 `sprintf') may contain [gtn]roff font changes, size changes, and local
2650 motions, provided those changes are undone before the end of the current
2653 A position is an (x,y) coordinate pair. There are lots of different
2654 ways to specify positions:
2658 <position-not-place>
2664 <position-not-place> ::=
2666 <position> + <expr-pair>
2667 <position> - <expr-pair>
2668 ( <position> , <position> )
2669 <expr> [of the way] between <position> and <position>
2670 <expr> '<' <position> , <position> '>'
2685 <corner> [of] <label>
2700 .ne | .se | .nw | .sw
2701 .c[enter] | .start | .end
2702 .t[op] | .b[ot[tom]] | .l[eft] | .r[ight]
2703 left | right | <top-of> | <bottom-of>
2704 <north-of> | <south-of> | <east-of> | <west-of>
2705 <center-of> | <start-of> | <end-of>
2706 upper left | lower left | upper right | lower right
2711 <\,\f(CIxxx\/\fP-of> ::=
2712 \f(CIxxx\fP \fR# followed by `of'\fP
2718 <ordinal> <object-type>
2719 [<ordinal>] last <object-type>
2726 INT st | INT nd | INT rd
2745 As Kernighan notes, \[lq]since barbarisms like \fB1th\fP and \fB3th\fP are
2746 barbaric, synonyms like \fB1st\fP and \fB3rd\fP are accepted as well.\[rq]
2747 Objects of a given type are numbered from 1 upwards in order of
2748 declaration; the \fBlast\fP modifier counts backwards.
2750 The \[lq]'th\[rq] form (which allows you to select a previous object with
2751 an expression, as opposed to a numeric literal) is not documented in DWB's
2754 The \[la]\,\fIxxx\/\fP-of\|\[ra] rule is special: The lexical parser checks whether
2755 \fIxxx\fP is followed by the token `of' without eliminating it so that
2756 the grammar parser can still see `of'. Valid examples of specifying a
2757 place with corner and label are thus
2774 both cause a syntax error. (DWB \fBpic\fP also allows the weird form
2777 Here the special rules for the `with' keyword using a path:
2782 ( <relative-path> , <relative-path> )
2789 . LABEL [. LABEL ...] [<corner>]
2793 The following style variables control output:
2795 center tab(@), linesize(2);
2799 Style Variable@Default@What It Does
2804 boxht@0.5@Default height of a box
2805 boxwid@0.75@Default height of a box
2806 lineht@0.5@Default length of vertical line
2807 linewid@0.75@Default length of horizontal line
2808 arcrad @0.25@Default radius of an arc
2809 circlerad@0.25@Default radius of a circle
2810 ellipseht@0.5@Default height of an ellipse
2811 ellipsewid@0.75@Default width of an ellipse
2812 moveht@0.5@Default length of vertical move
2813 movewid@0.75@Default length of horizontal move
2814 textht@0@Default height of box enclosing a text object
2815 textwid@0@Default width of box enclosing a text object
2816 arrowht@0.1@Length of arrowhead along shaft
2817 arrowwid@0.05@Width of rear of arrowhead
2818 arrowhead@1@Enable/disable arrowhead filling
2819 dashwid@0.05@Interval for dashed lines
2820 maxpswid@11@Maximum width of picture
2821 maxpsht@8.5@Maximum height of picture
2822 scale@1@Unit scale factor
2823 fillval@0.5@Default fill value
2827 Any of these can be set by assignment, or reset using the \fBreset\fP
2828 statement. Style variables assigned within `[\ ]' blocks are restored to
2829 their beginning-of-block value on exit; top-level assignments persist
2830 across pictures. Dimensions are divided by \fBscale\fR on output.
2832 All \fBpic\fP expressions are evaluated in floating point; units
2833 are always inches (a trailing `i' or `I' is ignored). Expressions have
2834 the following simple grammar, with semantics very similar to
2841 <place> <place-attribute>
2846 <func1> ( <any-expr> )
2847 <func2> ( <any-expr> , <any-expr> )
2854 .x | .y | .h[eigh]t | .wid[th] | .rad
2860 + | - | * | / | % | ^ | '<' | '>' | '<=' | '>='
2866 sin | cos | log | exp | sqrt | int | rand | srand
2876 Both \fBexp\fP and \fBlog\fP are base 10; \fBint\fP does integer
2877 truncation; and \fBrand()\fP returns a random number in [0-1).
2879 There are \fBdefine\fP and \fBundef\fR statements which are not part
2880 of the grammar (they behave as pre-processor macros to the language).
2881 These may be used to define pseudo-functions.
2884 \fBdefine\fP \fIname\fP \fB{\fP \fIreplacement-text\fP \fB}\fP
2888 This defines \fIname\fR as a macro to be replaced by the replacement
2889 text (not including the braces). The macro may be called as
2892 \fIname\/\fB(\,\fIarg1, arg2, .\|.\|., argn\fB\/)\fR
2896 The arguments (if any) will be substituted for tokens $1, $2 .\|.\|.\& $n
2897 appearing in the replacement text. To undefine a macro, say \fBundef\fP
2898 \fIname\fR, specifying the name to be undefined.
2903 History and Acknowledgements
2905 Original \fBpic\fP was written to go with Joseph Ossanna's original
2906 \fItroff\/\fP(1) by Brian Kernighan, and later re-written by Kernighan
2907 with substantial enhancements (apparently as part of the evolution of
2908 \fItroff\/\fP(1) into \fIditroff\/\fP(1) to generate
2909 device-independent output).
2911 The language had been inspired by some earlier graphics languages
2912 including \fBideal\fP and \fBgrap\fP. Kernighan credits Chris van Wyk
2913 (the designer of \fBideal\fP) with many of the ideas that went into
2916 .\" the original definitions of EQ and EN cause insertion of vertical
2917 .\" space which is not appropriate here
2925 The \fBpic\fP language was originally described by Brian Kernighan in
2926 Bell Labs Computing Science Technical Report #116 (you can obtain a
2927 PostScript copy of the revised version, [1], by sending a mail message to
2928 \fInetlib@research.att.com\fP with a body of `send 116 from
2929 research/cstr'). There have been two revisions, in 1984 and 1991.
2931 The document you are reading effectively subsumes Kernighan's
2932 description; it was written to fill in lacun\[ae] in the exposition and
2933 integrate in descriptions of the GNU \fIgpic\/\fP(1) features.
2935 The GNU \fBgpic\fR implementation was written by James Clark
2936 \[la]\,\fIjjc@jclark.com\/\fP\[ra]. It is currently maintained by Werner
2937 Lemberg \[la]\,\fIwl@gnu.org\/\fP\[ra].
2943 Kernighan, B. W. \fBPIC \[em] A Graphics Language for Typesetting
2944 (Revised User Manual)\fP. Bell Labs Computing Science Technical Report
2945 #116, December 1991.
2947 Van Wyk, C. J. \fBA high-level language for specifying pictures\fP.
2948 \fIACM Transactions On Graphics\fP 1,2 (1982) 163-182.