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.
16 .ie t .ds tx T\h'-.1667m'\v'.224m'E\v'-.224m'\h'-.125m'X
19 .de CE\" Centered caption for figure. Assumes previous .KS
25 .\" Definitions end here
27 Making Pictures With GNU PIC
31 \[la]\fIesr@snark.thyrsus.com\fP\[ra]
33 The \fBpic\fP language is a \fBtroff\fP extension that makes it easy
34 to create and alter box-and-arrow diagrams of the kind frequently used
35 in technical papers and textbooks. This paper is both an introduction
36 to and reference for \fIgpic\/\fP(1), the implementation distributed by
37 the Free Software Foundation for use with \fIgroff\/\fP(1).
45 The \fBpic\fP language provides an easy way to write procedural
46 box-and-arrow diagrams to be included in \fBtroff\fP documents. The
47 language is sufficiently flexible to be quite useful for state charts,
48 Petri-net diagrams, flow charts, simple circuit schematics, jumper
49 layouts, and other kinds of illustration involving repetitive uses of
50 simple geometric forms and splines. Because these descriptions are
51 procedural and object-based, they are both compact and easy to modify.
53 The \fIgpic\/\fP(1) implementation of \fBpic\fP is distributed by the
54 Free Software Foundation for use with their \fIgroff\/\fP(1)
55 implementation of \fBtroff\fP. Because both implementations are
56 widely available in source form for free, they are good bets for
57 writing very portable documentation.
61 The original 1984 pre-\fIditroff\/\fP(1) version of \fBpic\fP is long
62 obsolete. The rewritten 1991 version is still available as part of
63 the Documenter's Work Bench module of System V.
65 Where differences between Documenter's Work Bench (1991) \fBpic\fP and GNU
66 \fBpic\fP need to be described, original \fBpic\fP is referred to as
67 \[lq]DWB pic\[rq]. Details on the history of the program are given at the
70 In this document, the \fIgpic\/\fP(1) extensions will be marked as such.
74 Every \fBpic\fP description is a little program, which gets compiled
75 by \fIpic\/\fP(1) into \fIgtroff\/\fP(1) macros. Programs that process or
76 display \fIgtroff\/\fP(1) output need not know or care that parts of the
77 image began life as \fBpic\fP descriptions.
79 The \fIpic\/\fP(1) program tries to translate anything between \fB.PS\fP
80 and \fB.PE\fP markers, and passes through everything else. The normal
81 definitions of \fB.PS\fP and \fB.PE\fP in the \fIms\fP macro package
82 and elsewhere have also the side-effect of centering the \fBpic\fP output
87 If you make a \fBpic\fP syntax error, \fIgpic\/\fP(1) will issue an
88 error message in the standard \fIgcc\/\fP(1)-like syntax. A typical
89 error message looks like this,
93 pic:pic.ms:<nnn>: parse error before `<token>'
94 pic:pic.ms:<nnn>: giving up on this picture
99 where \[la]nnn\[ra] is a line number, and \[la]token\[ra] is a token near (usually
100 just after) the error location.
104 Pictures are described procedurally, as collections of objects
105 connected by motions. Normally, \fBpic\fP tries to string together
106 objects left-to-right in the sequence they are described, joining them
107 at visually natural points. Here is an example illustrating the
108 flow of data in \fBpic\fP processing:
113 box "\fIgpic\/\fP(1)"
115 box width 1.2 "\fIgtbl\/\fP(1) or \fIgeqn\/\fP(1)" "(optional)" dashed;
117 box "\fIgtroff\/\fP(1)";
121 .CE "1: Flow of \fBpic\fP data"
123 This was produced from the following \fBpic\fP program:
134 box width 1.2 "\efIgtbl\e/\efP(1) or \efIgeqn\e/\efP(1)" "(optional)" dashed;
136 box "\efIgtroff\e/\efP(1)";
144 This little program illustrates several \fBpic\fP basics. Firstly, we
145 see how to invoke three object types; ellipses, arrows, and boxes. We
146 see how to declare text lines to go within an object (and that text
147 can have font changes in it). We see how to change the line style of
148 an object from solid to dashed. And we see that a box can be made
149 wider than its default size to accommodate more text (we'll discuss
150 this facility in detail in the next section).
152 We also get to see \fBpic\fP's simple syntax. Statements are ended by
153 newlines or semicolons. String quotes are required around all text
154 arguments, whether or not they contain spaces. In general, the order
155 of command arguments and modifiers like \[lq]width 1.2\[rq] or
156 \[lq]dashed\[rq] doesn't matter, except that the order of text arguments
159 Here are all but one of the basic \fBpic\fP objects at their default sizes:
172 arc; down; move; "arc"
174 .CE "2: Basic \fBpic\fP objects"
176 The missing simple object type is a \fIspline\fP. There is also a way
177 to collect objects into \fIblock composites\fP which allows you to
178 treat the whole group as a single object (resembling a box) for many
179 purposes. We'll describe both of these later on.
181 The box, ellipse, circle, and block composite objects are \fIclosed\/\fR;
182 lines, arrows, arcs and splines are \fIopen\fP. This distinction
183 will often be important in explaining command modifiers.
185 Figure \n[H1]-2 was produced by the following \fBpic\fP program,
186 which introduces some more basic concepts:
201 arc; down; move; "arc"
207 The first thing to notice is the \fImove\fP command, which moves a
208 default distance (1/2 inch) in the current movement direction.
210 Secondly, see how we can also decorate lines and arrows with text.
211 The line and arrow commands each take two arguments here, specifying
212 text to go above and below the object. If you wonder why one argument
213 would not do, contemplate the output of \fBarrow "ow!"\fP:
218 .CE "3: Text centered on an arrow"
220 When a command takes one text string, \fBpic\fP tries to place it at
221 the object's geometric center. As you add more strings, \fBpic\fP
222 treats them as a vertical block to be centered. The program
229 line "1" "2" "3" "4";
230 line "1" "2" "3" "4" "5";
235 for example, gives you this:
242 line "1" "2" "3" "4";
243 line "1" "2" "3" "4" "5";
246 .CE "4: Effects of multiple text arguments"
248 The last line of Figure 3.2's program, `\fBarc; down; move;
249 "arc"\fP', describing the captioned arc, introduces several new ideas.
250 Firstly, we see how to change the direction in which objects are
251 joined. Had we written \fBarc; move; "arc"\fP,
252 omitting \fBdown\fP the caption would have been joined to the top
253 of the arc, like this:
258 .CE "5: Result of \fBarc; move; \"arc\"\fP"
260 This is because drawing an arc changes the default direction to the
261 one its exit end points at. To reinforce this point, consider:
266 .CE "6: Result of \fBarc cw; move; \"arc\"\fP"
268 All we've done differently here is specify \[lq]cw\[rq] for a clockwise arc
269 (\[lq]ccw\[rq] specifies counter-clockwise direction).
270 Observe how it changes the default direction to down, rather than up.
272 Another good way to see this via with the following program:
276 line; arc; arc cw; line
284 line; arc; arc cw; line;
286 .CE "7: Result of \fBline; arc; arc cw; line\fP"
288 Notice that we did not have to specify \[lq]up\[rq] for the second arc to be
289 joined to the end of the first.
291 Finally, observe that a string, alone, is treated as text to be
292 surrounded by an invisible box of a size either specified by width
293 and height attributes or by the defaults \fBtextwid\fR and
294 \fBtextht\fR. Both are initially zero (because we don't know the
299 Sizes are specified in inches. If you don't like inches, it's
300 possible to set a global style variable \fBscale\fP that changes the
301 unit. Setting \fBscale = 2.54\fP will effectively change the internal
302 unit to centimeters (all other size variable values will be scaled
305 Default Sizes of Objects
307 Here are the default sizes for \fBpic\fP objects:
309 center, tab(@), linesize(2);
318 box@0.75" wide by 0.5" high
320 ellipse@0.75" wide by 0.5" high
328 The simplest way to think about these defaults is that they make the
329 other basic objects fit snugly into a default-sized box.
331 Objects Do Not Stretch!
333 Text is rendered in the current font with normal troff line spacing.
334 Boxes, circles, and ellipses do \fInot\fP automatically resize to fit
335 enclosed text. Thus, if you say \fBbox "this text far too long for a
336 default box"\fP you'll get this:
339 box "this text is far too long for a default box"
341 .CE "1: Boxes do not automatically resize"
343 which is probably not the effect you want.
347 To change the box size, you can specify a box width with the \[lq]width\[rq]
351 box width 3 "this text is far too long for a default box"
353 .CE "2: Result of \fBbox width 3 \"text far too long\"\fP"
355 This modifier takes a dimension in inches. There is also a \[lq]height\[rq]
356 modifier that will change a box's height. The \fBwidth\fP keyword may
357 be abbreviated to \fBwid\fP; the \fBheight\fP keyword to \fBht\fP.
359 Resizing Other Object Types
361 To change the size of a circle, give it a \fBrad[ius]\fP or
362 \fBdiam[eter]\fP modifier; this changes the radius or diameter of the
363 circle, according to the numeric argument that follows.
366 {circle rad 0.1; move down 0.2 from last circle .s; "0.1"};
367 move; circle rad 0.2 "0.2"; move; circle rad 0.3 "0.3";
369 .CE "3: Circles with increasing radii"
371 The \fBmove\fP command can also take a dimension, which just tells
372 it how many inches to move in the current direction.
374 Ellipses are sized to fit in the rectangular box defined by their
375 axes, and can be resized with \fBwidth\fP and \fBheight\fP like boxes.
377 You can also change the radius of curvature of an arc with \fBrad[ius]\fP
378 (which specifies the radius of the circle of which the arc is a segment).
379 Larger values yield flatter arcs.
382 {arc rad 0.1; move down 0.3 from last arc .center; "0.1"};
384 {arc rad 0.2; move down 0.4 from last arc .center; "0.2"};
386 {arc rad 0.3; move down 0.5 from last arc .center; "0.3"};
388 .CE "4: \fBarc rad\fP with increasing radii"
390 Observe that because an arc is defined as a quarter circle, increasing
391 the radius also increases the size of the arc's bounding box.
395 In place of a dimension specification, you can use the keyword
396 \fBsame\fR. This gives the object the same size as the previous one
397 of its type. As an example, the program
402 box; box wid 1 ht 1; box same; box
411 box; box wid 1 ht 1; box same; box
413 .CE "5: The \fBsame\fP keyword"
416 Generalized Lines and Splines
420 It is possible to specify diagonal lines or arrows by adding multiple \fBup\fP,
421 \fBdown\fP, \fBleft\fP, and \fBright\fP modifiers to the line object.
422 Any of these can have a multiplier. To understand the effects, think
423 of the drawing area as being gridded with standard-sized boxes.
426 # Draw a demonstration up left arrow with grid box overlay
432 box wid 0.5 ht 0.5 dotted with .nw at last arrow .end;
433 for i = 2 to ($1 / 0.5) do {
434 box wid 0.5 ht 0.5 dotted with .sw at last box .se;
436 move down from last arrow .center;
438 if ( $1 == boxht ) then {
441 sprintf("\fBarrow up left %g\fP", $1)
445 move right 0.1 from last [] .e;
453 .CE "1: Diagonal arrows (dotted boxes show the implied 0.5-inch grid)"
455 Multi-Segment Line Objects
457 A \[lq]line\[rq] or \[lq]arrow\[rq] object may actually be a path
458 consisting of any number of segments of varying lengths and directions.
459 To describe a path, connect several line or arrow commands with the
463 define zigzag { $1 right 1 then down .5 left 1 then right 1 }
466 .CE "2: \fBline right 1 then down .5 left 1 then right 1\fP"
470 If you start a path with the \fBspline\fP keyword, the path vertices
471 are treated as control points for a spline curve fit.
475 move down 0.2 from last [] .s;
476 "The spline curve..."
477 move right from last [] .e;
480 spline from start of last line right 1 then down .5 left 1 then right 1;
481 "1" at last spline .start + (-0.1, 0);
482 "2" at last spline .start + (1.1, 0);
483 "3" at last spline .end + (-1.1, 0);
484 "4" at last spline .end + (0.1, 0);
486 move down 0.2 from last [] .s;
487 "...with tangents displayed"
490 .CE "3: \fBspline right 1 then down .5 left 1 then right 1\fP"
492 You can describe many natural-looking but irregular curves this
496 [spline right then up then left then down ->;]
497 move down 0.2 from last [] .s;
498 ["\fBspline right then up then left then down ->;\fP"]
499 move right 3 from last [] .se;
500 "\fBspline left then up right then down right ->;\fP"
502 [spline left then up right then down right ->;]
504 .CE "4: Two more spline examples"
506 Note the arrow decorations. Arrowheads can be applied naturally to
507 any path-based object, line or spline. We'll see how in the next
514 We've already seen that the modifier \fBdashed\fP can change the line
515 style of an object from solid to dashed. GNU \fBgpic\fP permits you to
516 dot or dash ellipses, circles, and arcs (and splines in \*[tx] mode
517 only); some versions of DWB may only permit dashing of lines and
518 boxes. It's possible to change the dash interval by specifying a
519 number after the modifier.
523 box dashed "default";
525 box dashed 0.05 "0.05";
527 box dashed 0.1 "0.1";
529 box dashed 0.15 "0.15";
531 box dashed 0.2 "0.2";
533 .CE "1: Dashed objects"
537 Another available qualifier is \fBdotted\fP. GNU \fBgpic\fP permits
538 you to dot or dash ellipses, circles, and arcs (and splines in \*[tx]
539 mode only); some versions of DWB may only permit dashing of lines and
540 boxes. It too can be suffixed with a number to specify the interval
544 box dotted "default";
546 box dotted 0.05 "0.05";
548 box dotted 0.1 "0.1";
550 box dotted 0.15 "0.15";
552 box dotted 0.2 "0.2";
554 .CE "2: Dotted objects"
558 It is also possible, in GNU \fBgpic\fP only, to modify a box so it has
562 box rad 0.05 "rad 0.05";
564 box rad 0.1 "rad 0.1";
566 box rad 0.15 "rad 0.15";
568 box rad 0.2 "rad 0.2";
570 box rad 0.25 "rad 0.25";
572 .CE "3: \fBbox rad\fP with increasing radius values"
574 Radius values higher than half the minimum box dimension are silently
575 truncated to that value.
579 Lines and arcs can be decorated as well. Any line or arc (and any
580 spline as well) can be decorated with arrowheads by adding one or more
586 .CE "4: Double-headed line made with \fBline <- ->\fP"
588 In fact, the \fBarrow\fP command is just shorthand for \fBline ->\fP. And
589 there is a double-head modifier <->, so the figure above could have been made
592 Arrowheads have a \fBwidth\fP attribute, the distance across the rear;
593 and a \fBheight\fP attribute, the length of the arrowhead along the shaft.
595 Arrowhead style is controlled by the style variable \fBarrowhead\fP.
596 The DWB and GNU versions interpret it differently. DWB defaults to
597 open arrowheads and an \fBarrowhead\fP value of 2; the Kernighan
598 paper says a value of 7 will make solid arrowheads. GNU \fBgpic\fP
599 defaults to solid arrowheads and an \fBarrowhead\fP value of 1; a
600 value of 0 will produce open arrowheads.
604 It's also possible to change the line thickness of an object (this is
605 a GNU extension, DWB \fBpic\fP doesn't support it).
606 The default thickness of the lines used to draw objects is controlled by the
609 This gives the thickness of lines in points.
610 A negative value means use the default thickness:
611 in \*[tx] output mode, this means use a thickness of 8 milliinches;
612 in \*[tx] output mode with the
614 option, this means use the line thickness specified by
616 lines; in troff output mode, this means use a thickness proportional
617 to the pointsize. A zero value means draw the thinnest possible line
618 supported by the output device. Initially it has a value of -1.
619 There is also a \fBthickness\fP attribute (which can be abbreviated to
620 \fBthick\fP). For example, \fBcircle thickness 1.5\fP would draw a
621 circle using a line with a thickness of 1.5 points. The thickness of
622 lines is not affected by the value of the
624 variable, nor by any width or height given in the
630 The modifier \fBinvis[ible]\fP makes an object entirely invisible. This
631 used to be useful for positioning text in an invisible object that is
632 properly joined to neighboring ones. Newer DWB versions and GNU
633 \fBpic\fP treat stand-alone text in exactly this way.
637 It is possible to fill boxes, circles, and ellipses. The
638 modifier \fBfill[ed]\fP accomplishes this. You can suffix it with a fill
639 value; the default is given by the stule variable \fBfillval\fP.
641 DWB \fBpic\fP and \fBgpic\fP have opposite conventions for fill values
642 and different defaults. DWB \fBfillval\fP defaults to 0.3 and smaller
643 values are darker; GNU \fBfillval\fP uses 0 for white and 1 for black.
646 circle fill; move; circle fill 0.4; move; circle fill 0.9;
648 .CE "5: \fBcircle fill; move; circle fill 0.4; move; circle fill 0.9;\fR"
650 GNU \fBgpic\fP makes some additional guarantees. A fill value greater
651 than 1 can also be used: this means fill with the shade of gray that
652 is currently being used for text and lines. Normally this will be
653 black, but output devices may provide a mechanism for changing this.
654 The invisible attribute does not affect the filling of objects. Any
655 text associated with a filled object will be added after the object
656 has been filled, so that the text will not be obscured by the filling.
658 The closed-object modifier \fBsolid\fP is equivalent to \fBfill\fP
659 with the darkest fill value (DWB \fBpic\fP had this capability but
660 mentioned it only in a reference section).
664 As a GNU extension, three additional modifiers are available to specify
665 colored objects. \fBoutline\fP sets the color of the outline, \fBshaded\fP
666 the fill color, and \fBcolor\fP sets both. All three keywords expect a
667 suffix specifying the color. Example:
670 box color "yellow"; arrow color "cyan"; circle shaded "green" outline "black";
672 .CE "6: \fBbox color ""yellow""; arrow color ""cyan""; \
673 circle shaded ""green"" outline ""black"";\fR"
675 Alternative spellings are \fBcolour\fP, \fBcolored\fP, \fBcoloured\fP,
678 Currently, color support is not available in \*[tx] mode. Predefined color
679 names for \fIgroff\/\fP(1) are in the device macro files, for example
680 \f(CWps.tmac\fP; additional colors can be defined with the \fB.defcolor\fP
681 request (see the manual page of GNU \fItroff\/\fP(1) for more details).
683 More About Text Placement
685 By default, text is centered at the geometric center of the object it is
686 associated with. The modifier \fBljust\fP causes the left end to be
687 at the specified point (which means that the text lies to the right of
688 the specified place!), the modifier \fBrjust\fP puts the right end at
689 the place. The modifiers \fBabove\fP and \fBbelow\fP center the text
690 one half line space in the given direction.
692 Text attributes can be combined:
695 [line up "ljust text" ljust;]
697 [line up "rjust text" rjust;]
699 [arrow 1 "ljust above" ljust above;]
701 [arrow 1 "rjust below" rjust below;]
703 .CE "1: Text attributes"
705 What actually happens is that \fIn\fP text strings are centered in a box
706 that is \fBtextwid\fP wide by \fBtextht\fP high. Both these variables
707 are initially zero (that is \fBpic\fR's way of not making assumptions
708 about \fI[tg]roff\/\fP(1)'s default point size).
710 In GNU \fBgpic\fR, objects can have an
713 This will only work when the postprocessor is
715 Any text associated with an object having the
717 attribute will be rotated about the center of the object
718 so that it is aligned in the direction from the start point
719 to the end point of the object.
720 Note that this attribute will have no effect for objects whose start and
721 end points are coincident.
723 More About Direction Changes
725 We've already seen how to change the direction in which objects are
726 composed from rightwards to downwards. Here are some more
727 illustrative examples:
732 "\fBright; box; arrow; circle; arrow; ellipse\fP";
734 [right; box; arrow; circle; arrow; ellipse;]
736 move down 0.3 from last [] .s;
738 "\fBleft; box; arrow; circle; arrow; ellipse\fP"
740 [left; box; arrow; circle; arrow; ellipse;]
742 # move down 0.3 from last [] .sw;
743 # To re-join this illustrations, delete everything from here down to
744 # the next #-comment, and uncomment the move line above
746 .CE "1: Effects of different motion directions (right and left)"
749 # To re-join this illustrations, delete everything down to here, then
750 # comment out the next `down' line.
751 # Don't forget to re-number the figures following!
754 "\fBdown; box; arrow; circle; arrow; ellipse;\fP"
756 box; arrow; circle; arrow; ellipse;
758 move right 2 from last [] .e;
760 up; box; arrow; circle; arrow; ellipse;
762 "\fBup; box; arrow; circle; arrow; ellipse;\fP"
765 .CE "2: Effects of different motion directions (up and down)"
767 Something that may appear surprising happens if you change directions
771 box; arrow; circle; down; arrow; ellipse
773 .CE "3: \fBbox; arrow; circle; down; arrow; ellipse\fP"
775 You might have expected that program to yield this:
778 box; arrow; circle; move to last circle .s; down; arrow; ellipse
780 .CE "4: More intuitive?"
782 But, in fact, to get Figure \*[SN]3 you have to do this:
790 move to last circle .s;
799 Why is this? Because the exit point for the current direction is
800 already set when you draw the object. The second arrow in Figure
801 \*[SN]2 dropped downwards from the circle's attachment point for an
802 object to be joined to the right.
804 The meaning of the command \fBmove to last circle .s\fP should be obvious.
805 In order to see how it generalizes, we'll need to go into detail on two
806 important topics; locations and object names.
810 The most natural way to name locations in \fBpic\fP is relative to
811 objects. In order to do this, you have to be able you have to be able
812 to name objects. The \fBpic\fP language has rich facilities for this
813 that try to emulate the syntax of English.
815 Naming Objects By Order Of Drawing
817 The simplest (and generally the most useful) way to name an object is
818 with a \fBlast\fP clause. It needs to be followed by an object type
819 name; \fBbox\fP, \fBcircle\fP, \fBellipse\fP, \fBline\fP, \fBarrow\fP,
820 \fBspline\fP, \fB""\fP, or \fB[]\fP (the last type refers to a \fIcomposite
821 object\fP which we'll discuss later). So, for example, the \fBlast
822 circle\fP clause in the program attached to Figure \*[SN]3 refers to the
825 More generally, objects of a given type are implicitly numbered
826 (starting from\~1). You can refer to (say) the third ellipse in the
827 current picture with \fB3rd ellipse\fP, or to the first box as \fB1st
828 box\fP, or to the fifth text string (which isn't an attribute to another
829 object) as \fB5th ""\fP.
831 Objects are also numbered backwards by type from the last one.
832 You can say \fB2nd last box\fP to get the second-to-last box, or
833 \fB3rd last ellipse\fP to get the third-to-last ellipse.
835 In places where \fIn\/\fBth\fR is allowed, \fB`\fIexpr\/\fB'th\fR is
836 also allowed. Note that
838 is a single token: no space is allowed between the
847 line from `i'th box.nw to `i+1'th box.se
853 Naming Objects With Labels
855 You can also specify an object by referring to a label. A label is a
856 word (which must begin with a capital letter) followed by a colon;
857 you declare it by placing it immediately before the object drawing command.
858 For example, the program
863 A: box "first" "object"
865 B: ellipse "second" "object"
873 declares labels \fBA\fP and \fBB\fP for its first and second objects.
874 Here's what that looks like:
877 A: box "first" "object"
879 B: ellipse "second" "object"
883 .CE "1: Example of label use"
884 The \fBat\fP statement in the fourth line uses the label \fBA\fP (the
885 behavior of \fBat\fP will be explained in the next section). We'll
886 see later on that labels are most useful for referring to block composite
889 Labels are not constants but variables (you can view colon as a sort
890 of assignment). You can say something like \fBA: A + (1,0);\fP
891 and the effect will be to reassign the label \fBA\fR to designate a
892 position one inch to the right of its old value.
896 The location of points can be described in many different ways. All these
897 forms are interchangeable as for as the \fBpic\fP language syntax is
898 concerned; where you can use one, any of the others that would make
899 semantic sense are allowed.
901 The special label \fBHere\fR always refers to the current position.
905 The simplest is absolute coordinates in inches; \fBpic\fP uses a
906 Cartesian system with (0, 0) at the lower left corner of the virtual
907 drawing surface for each picture (that is, X increases to the right
908 and Y increases upwards). An absolute location may always be written in the
909 conventional form as two comma-separated numbers surrounded by
910 parentheses (and this is recommended for clarity). In contexts where
911 it creates no ambiguity, the pair of X and Y coordinates suffices
914 It is a good idea to avoid absolute coordinates, however. They tend
915 to make picture descriptions difficult to understand and modify.
916 Instead, there are quite a number of ways to specify locations
917 relative to \fBpic\fP objects and previous locations.
920 Locations Relative to Objects
922 The symbol \fBHere\fP always refers to the position of the last object
923 drawn or the destination of the last \fBmove\fP.
925 Alone and unqualified, a \fBlast circle\fP or any other way of
926 specifying a closed-object or arc location refers as a position to the
927 geometric center of the object. Unqualified, the name of a line or
928 spline object refers to the position of the object start.
930 Also, \fBpic\fP objects have quite a few named locations
931 associated with them. One of these is the object center, which can be
932 indicated (redundantly) with the suffix \fB.center\fP (or just \fB.c\fP).
933 Thus, \fBlast circle \&.center\fP is equivalent to \fBlast
936 Locations Relative to Closed Objects
938 Every closed object (box, circle, ellipse, or block composite) also
939 has eight compass points associated with it;
942 define dot {circle fill rad 0.02 at $1}
946 dot(ME.c); "\fB .c\fP" at ME .c ljust;
947 dot(ME.n); "\fB.n\fP" at ME .n above
948 dot(ME.ne); "\fB .ne\fP" at ME .ne above
949 dot(ME.e); "\fB .e\fP" at ME .e ljust
950 dot(ME.se); "\fB .se\fP" at ME .se below
951 dot(ME.s); "\fB.s\fP" at ME .s below
952 dot(ME.sw); "\fB.sw \fP" at ME .sw below
953 dot(ME.w); "\fB.w \fP" at ME .w rjust
954 dot(ME.nw); "\fB.nw \fP" at ME .nw above
956 compass(box wid 1.5 ht 1);
957 move right from last [] .e;
958 compass(circle diam 1);
959 move right from last [] .e;
960 compass(ellipse wid 1.5 ht 1);
962 .CE "1: Compass points"
964 these are the locations where eight compass rays from the geometric center
965 would intersect the figure. So when we say \fBlast circle .s\fP we are
966 referring to the south compass point of the last circle drawn. The
967 explanation of Figure 7.3's program is now complete.
969 (In case you dislike compass points, the names \fB.top\fP,
970 \&\fB.bottom\fP, \fB.left\fP and \fB.right\fP are synonyms for \fB.n\fP,
971 \&\fB.s\fP, \fB.e\fP, and \fB.w\fP respectively; they can even be
972 abbreviated to \fB.t\fP, \fB.b\fP, \fB.l\fP and \fB.r\fP).
974 The names \fBcenter\fP, \fBtop\fP, \fBbottom\fP, \fBleft\fP, \fBright\fP,
975 \fBnorth\fP, \fBsouth\fP, \fBeast\fP, and \fBwest\fP can also be used
976 (without the leading dot) in a prefix form marked by \fBof\fP; thus,
977 \fBcenter of last circle\fP and \fBtop of 2nd last ellipse\fP are both
978 valid object references. Finally, the names \fBleft\fP and \fBright\fP
979 can be prefixed with \fBupper\fP and \fBlower\fP which both have the
982 Arc objects also have compass point; they are the compass points of
985 Locations Relative to Open Objects
987 Every open object (line, arrow, arc, or spline) has three named
988 points: \fB.start\fP, \fB.center\fP (or \fB.c\fP), and \fB.end\fP. They
989 can also be used without leading dots in the \fBof\fP prefix form.
990 The center of an arc is the center of its circle, but the center of
991 a line, path, or spline is halfway between its endpoints.
996 dot(ME.c); "\fB.center\fP" rjust at ME.center + (-0.1, 0.1)
997 dot(ME.start); "\fB.start\fP" rjust at ME.start + (-0.1, 0.1)
998 dot(ME.end); "\fB.end\fP" rjust at ME.end + (-0.1, 0.1)
1001 critical(line up right 1);
1002 move right 1 from last [] .e;
1003 critical(arc rad 0.5 cw);
1004 move down 0.5 from 2nd last [] .s;
1005 critical(line right 1 then down .5 left 1 then right 1);
1006 move right 1 from last [] .e;
1007 critical(spline right 1 then up right then left then left 1);
1009 .CE "2: Special points on open objects"
1012 Ways of Composing Positions
1014 Once you have two positions to work with, there are several ways to
1015 combine them to specify new positions.
1017 Vector Sums and Displacements
1019 Any two positions may be added or subtracted to yield a new position.
1020 The result is the conventional vector sum or difference of coordinates.
1021 For example, \fBlast box .ne + (0.1, 0)\fP is a valid position. This
1022 example illustrates a common use, to define a position slightly offset
1023 from a named one (say, for captioning purposes).
1025 Interpolation Between Positions
1027 A position may be interpolated between any two positions. The syntax
1028 is `\fIfraction\fP \fBof the way between\fP \fIposition1\fP \fBand\fP
1029 \fIposition2\fP'. For example, you can say \fB1/3 of the way between
1030 here and last ellipse .ne\fP. The fraction may be in
1031 numerator/denominator form or may be an ordinary number (values are
1032 \fInot\fP restricted to [0,1]). As an alternative to this verbose
1033 syntax, you can say `\fIfraction\fP \fB<\,\fP\fIposition1\fP \fB,\fP
1034 \fIposition2\/\fP\fB>\fP'; thus, the example could also be written as
1035 \fB1/3 <here, last ellipse>\fP.
1039 P: 1/3 of the way between last arrow .start and last arrow .end;
1040 dot(P); move right 0.1; "P";
1042 .CE "3: \fBP: 1/3 of the way between last arrow .start and last arrow .end\fP"
1044 This facility can be used, for example, to draw double connections.
1049 arrow right at 1/4 <A.e,A.ne>;
1050 arrow left at 1/4 <B.w,B.sw>;
1052 .CE "4: Doubled arrows"
1054 You can get Figure \n[H1]-4 from the following program:
1061 arrow right at 1/4 <A.e,A.ne>;
1062 arrow left at 1/4 <B.w,B.sw>;
1068 Note the use of the short form for interpolating points.
1070 Projections of Points
1072 Given two positions \fIp\fP and \fIq\fP, the position
1073 \fB(\,\fP\fIp\fP\fB,\fP \fIq\fP\fB)\fP has the X coordinate of \fIp\fP
1074 and the Y coordinate of \fIq\fP. This can be helpful in placing an
1075 object at one of the corners of the virtual box defined by two other
1079 box invis wid 2 height 1;
1080 dot(last box .ne); "\fB(B,A)\fP is here" ljust at last circle + (0.1, 0.1);
1081 dot(last box .se); "B" ljust at last circle + (0.1, -0.1)
1082 dot(last box .sw); "\fB(A,B)\fP is here" rjust at last circle + (-0.1, -0.1);
1083 dot(last box .nw); "A" ljust at last circle + (-0.1, 0.1)
1085 .CE "5: Using (\fIx\fP, \fIy\fP) composition"
1089 There are four ways to use locations; \fBat\fP, \fBfrom\fP, \fBto\fP,
1090 and \fBwith\fP. All three are object modifiers; that is, you use them
1091 as suffixes to a drawing command.
1093 The \fBat\fP modifier says to draw a closed object or arc with its
1094 center at the following location, or to draw a line/spline/arrow
1095 starting at the following location.
1097 The \fBto\fP modifier can be used alone to specify a move destination.
1098 The \fBfrom\fP modifier can be used alone in the same way as \fBat\fP.
1100 The \fBfrom\fP and \fBto\fP modifiers can be used with a \fBline\fR or
1101 \fBarc\fR command to specify start and end points of the object. In
1102 conjunction with named locations, this offers a very flexible
1103 mechanism for connecting objects. For example, the following program
1111 arc cw from 1/3 of the way \e
1112 between last box .n and last box .ne to last ellipse .n;
1124 arc cw from 1/3 of the way \
1125 between last box .n and last box .ne to last ellipse .n;
1127 .CE "6: A tricky connection specified with English-like syntax"
1129 The \fBwith\fP modifier allows you to identify a named attachment
1130 point of an object (or a position within the object) with another point.
1131 This is very useful for connecting objects in a natural way. For an
1132 example, consider these two programs:
1138 box wid 0.75 ht 0.75;
1140 move down 0.3 from last [] .s 0.1;
1141 "\fBbox wid 0.5 ht 0.5; box wid 0.75 ht 0.75\fP"
1143 move from last [].e 1.5
1147 box wid 0.75 ht 0.75 with .sw at last box .se;
1149 move down 0.3 from last [] .s 0.1;
1150 box invisible "\fBbox wid 0.5 ht 0.5;\fP" \
1151 "\fBbox wid 0.75 ht 0.75 with .sw at last box .se;\fP"
1154 .CE "7: Using the \fBwith\fP modifier for attachments"
1158 When drawing lines between circles that don't intersect them at a
1159 compass point, it is useful to be able to shorten a line by the radius
1160 of the circle at either or both ends. Consider the following program:
1166 circle "y" at 1st circle - (0.4, 0.6)
1167 circle "z" at 1st circle + (0.4, -0.6)
1168 arrow from 1st circle to 2nd circle chop
1169 arrow from 2nd circle to 3rd circle chop
1170 arrow from 3rd circle to 1st circle chop
1176 It yields the following:
1180 circle "y" at 1st circle - (0.4, 0.6)
1181 circle "z" at 1st circle + (0.4, -0.6)
1182 arrow from 1st circle to 2nd circle chop
1183 arrow from 2nd circle to 3rd circle chop
1184 arrow from 3rd circle to 1st circle chop
1186 .CE "8: The \fBchop\fR modifier"
1188 Notice that the \fBchop\fR attribute moves arrowheads rather than
1189 stepping on them. By default, the \fBchop\fR modifier shortens both
1190 ends of the line by \fBcirclerad\fR. By suffixing it with a number
1191 you can change the amount of chopping.
1193 If you say \fBline .\|.\|.\& chop \fIr1\fP chop \fIr2\fP\fR with \fIr1\fP
1194 and \fIr2\fP both numbers, you can vary the amount of chopping at both
1195 ends. You can use this in combination with trigonometric functions
1196 to write code that will deal with more complex intersections.
1200 There are two different ways to group objects in \fBpic\fP; \fIbrace
1201 grouping\fP and \fIblock composites\fP.
1205 The simpler method is simply to group a set of objects within curly
1206 bracket or brace characters. On exit from this grouping, the current
1207 position and direction are restored to their value when the opening
1208 brace was encountered.
1212 A block composite object is created a series of commands enclosed by
1213 square brackets. The composite can be treated for most purposes like
1214 a single closed object, with the size and shape of its bounding box.
1215 Here is an example. The program fragment
1221 line up 1 at last circle .n;
1222 line down 1 at last circle .s;
1223 line right 1 at last circle .e;
1224 line left 1 at last circle .w;
1225 box dashed with .nw at last circle .se + (0.2, -0.2);
1226 Caption: center of last box;
1232 yields the block in figure \n[H1]-1, which we show both with and
1233 without its attachment points. The block's location becomes the
1239 line up 1 at last circle .n;
1240 line down 1 at last circle .s;
1241 line right 1 at last circle .e;
1242 line left 1 at last circle .w;
1243 box dashed with .nw at last circle .se + (0.2, -0.2);
1244 Caption: center of last box;
1248 compass([junction()]);
1250 .CE "1: A sample composite object"
1252 To refer to one of the composite's attachment points, you can say
1253 (for example) \fBA .s\fP. For purposes of object naming, composites
1254 are a class. You could write \fBlast [] .s\fP as an equivalent
1255 reference, usable anywhere a location is needed. This construction is
1256 very important for putting together large, multi-part diagrams.
1258 Blocks are also a variable-scoping mechanism, like a \fIgroff\/\fP(1)
1259 environment. All variable assignments done inside a block are undone
1260 at the end of it. To get at values within a block, write a name of
1261 the block followed by a dot, followed by the label you
1262 want. For example, we could refer the the center of the box in the
1263 above composite as \fBlast [] .Caption\fP or \fBA.Caption\fP.
1265 This kind of reference to a label can be used in any way any other
1266 location can be. For example, if we added \fB"Hi!" at A.Caption\fP
1267 the result would look like this:
1273 .CE "2: Adding a caption using interior labeling"
1275 You can also use interior labels in either part of a \fBwith\fR
1276 modifier. This means that the example composite could be placed
1277 relative to its caption box by a command containing \fBwith A.Caption
1280 Note that both width and height of the block composite object are always
1287 box wid 0.75 ht 0.75
1289 move down 0.3 from last [].s 0.1
1290 "\fBbox wid -0.5 ht 0.5; box wid 0.75 ht 0.75\fP"
1292 move from last [].e 2
1295 [ box wid -0.5 ht 0.5 ]
1296 box wid 0.75 ht 0.75
1298 move down 0.3 from last [].s 0.1
1299 "\fB[box wid -0.5 ht 0.5]; box wid 0.75 ht 0.75\fP"
1302 .CE "3: Composite block objects always have positive width and height
1304 Blocks may be nested. This means you can use block attachment points
1305 to build up complex diagrams hierarchically, from the inside out.
1306 Note that \fBlast\fP and the other sequential naming mechanisms
1307 don't look inside blocks, so if you have a program that looks
1313 P: [box "foo"; ellipse "bar"];
1315 [box "baz"; ellipse "quxx"]
1318 arrow from 2nd last [];
1324 the arrow in the last line will be attached to object \fBP\fP, not
1327 In DWB \fBpic\fP, only references one level deep into enclosed blocks
1328 were permitted. GNU \fBgpic\fP removes this restriction.
1330 The combination of block variable scoping, assignability of labels and
1331 the macro facility that we'll describe later on can be used to
1332 simulate functions with local variables (just wrap the macro body in
1337 There are a number of global style variables in \fBpic\fR that can be used to
1338 change its overall behavior. We've mentioned several of them in
1339 previous sections. They're all described here. For each variable,
1340 the default is given.
1342 center, tab(@), linesize(2);
1346 Style Variable@Default@What It Does
1351 boxht@0.5@Default height of a box
1352 boxwid@0.75@Default width of a box
1353 lineht@0.5@Default length of vertical line
1354 linewid@0.75@Default length of horizontal line
1355 linethick@-1@Default line thickness
1356 arcrad @0.25@Default radius of an arc
1357 circlerad@0.25@Default radius of a circle
1358 ellipseht@0.5@Default height of an ellipse
1359 ellipsewid@0.75@Default width of an ellipse
1360 moveht@0.5@Default length of vertical move
1361 movewid@0.75@Default length of horizontal move
1362 textht@0@Default height of box enclosing a text object
1363 textwid@0@Default width of box enclosing a text object
1364 arrowht@0.1@Length of arrowhead along shaft
1365 arrowwid@0.05@Width of rear of arrowhead
1366 arrowhead@1@Enable/disable arrowhead filling
1367 dashwid@0.05@Interval for dashed lines
1368 maxpswid@11@Maximum width of picture
1369 maxpsht@8.5@Maximum height of picture
1370 scale@1@Unit scale factor
1371 fillval@0.5@Default fill value
1375 Any of these variables can be set with a simple assignment statement.
1379 [boxht=1; boxwid=0.3; movewid=0.2; box; move; box; move; box; move; box;]
1381 .CE "1: \fBboxht=1; boxwid=0.3; movewid=0.2; box; move; box; move; box; move; box;\fP"
1383 In GNU \fBpic\fR, setting the \fBscale\fR variable re-scales all
1384 size-related state variables so that their values remain equivalent in
1387 The command \fBreset\fP resets all style variables to their defaults.
1388 You can give it a list of variable names as arguments (optionally
1389 separated by commas), in which case it resets only those.
1391 State variables retain their values across pictures until reset.
1393 Expressions, Variables, and Assignment
1395 A number is a valid expression, of course (all numbers are stored
1396 internally as floating-point). Decimal-point notation is acceptable;
1397 in GNU \fBgpic\fR, scientific notation in C's `e' format (like
1398 \f(CW5e-2\fP) is accepted.
1400 Anywhere a number is expected, the language will also accept a
1401 variable. Variables may be the built-in style variable described in
1402 the last section, or new variables created by assignment.
1404 DWB \fBpic\fP supports only the ordinary assignment via \fB=\fP, which
1405 defines the variable (on the left side of the equal sign) in the current
1406 block if it is not already defined there, and then changes the value (on
1407 the right side) in the current block. The variable is not visible outside
1408 of the block. This is similar to the C\~programming language where a
1409 variable within a block shadows a variable with the same name outside of
1412 GNU \fBgpic\fP supports an alternate form of assignment using \fB:=\fP.
1413 The variable must already be defined, and the value will be assigned to
1414 that variable without creating a variable local to the current block.
1431 You can use the height, width, radius, and x and y coordinates of any
1432 object or corner in expressions. If \fBA\fP is an object label or name,
1433 all the following are valid:
1437 A.x # x coordinate of the center of A
1438 A.ne.y # y coordinate of the northeast corner of A
1439 A.wid # the width of A
1440 A.ht # and its height
1441 2nd last circle.rad # the radius of the 2nd last circle
1446 Note the second expression, showing how to extract a corner coordinate.
1448 Basic arithmetic resembling those of C operators are available; \fB+\fP,
1449 \fB*\fP, \fB-\fP, \fB/\fP, and \fB%\fP. So is \fB^\fP for exponentiation.
1450 Grouping is permitted in the usual way using parentheses. GNU \fBgpic\fP
1451 allows logical operators to appear in expressions; \fB!\&\fP (logical
1452 negation, not factorial), \fB&&\fP, \fB|\||\fP, \fB==\fP, \fB!=\fP,
1453 \fB>=\fP, \fB<=\fP, \fB<\fP, \fB>\fP.
1455 Various built-in functions are supported: \fBsin(\fIx\fB)\fR,
1456 \fBcos(\fIx\fB)\fR, \fBlog(\fIx\fB)\fR, \fBexp(\fIx\fB)\fR,
1457 \fBsqrt(\fIx\fB)\fR, \fBmax(\fIx\fB,\fIy\fB)\fR,
1458 \fBatan2(\fIx\fB,\fIy\fB)\fR, \fBmin(\fIx\fB,\fIy\fB)\fR,
1459 \fBint(\fIx\fB)\fR, \fBrand()\fP, and \fBsrand()\fP.
1460 Both \fBexp\fP and \fBlog\fP are
1461 base\~10; \fBint\fP does integer truncation; \fBrand()\fP returns a
1462 random number in [0-1), and \fBsrand()\fP sets the seed for
1463 a new sequence of pseudo-random numbers to be returned by \fBrand()\fP
1464 (\fBsrand()\fP is a GNU extension).
1466 GNU \fBgpic\fP also documents a one-argument form or rand,
1467 \fBrand(\fIx\fB)\fR, which returns a random number between 1 and
1468 \fIx\fP, but this is deprecated and may be removed in a future
1471 The function \fBsprintf()\fP behaves like a C \fIsprintf\/\fP(3)
1472 function that only takes %, %e, %f, and %g format strings.
1476 You can define macros in \fBpic\fP. This is useful for diagrams with
1477 repetitive parts. In conjunction with the scope rules for block
1478 composites, it effectively gives you the ability to write functions.
1483 \fBdefine\fP \fIname\fP \fB{\fP \fIreplacement text \fB}\fP
1487 This defines \fIname\fR as a macro to be replaced by the replacement
1488 text (not including the braces). The macro may be called as
1491 \fIname\fB(\fIarg1, arg2, \|.\|.\|.\& argn\fB)\fR
1495 The arguments (if any) will be substituted for tokens \fB$1\fP, \fB$2\fP
1496 \&.\|.\|.\& \fB$n\fP
1497 appearing in the replacement text.
1499 As an example of macro use, consider this:
1506 # Plot a single jumper in a box, $1 is the on-off state.
1509 Outer: box invis wid 0.45 ht 1;
1511 # Count on end ] to reset these
1512 boxwid = Outer.wid * shrinkfactor / 2;
1513 boxht = Outer.ht * shrinkfactor / 2;
1515 box fill (!$1) with .s at center of Outer;
1516 box fill ($1) with .n at center of Outer;
1519 # Plot a block of six jumpers.
1520 define jumperblock {
1528 jwidth = last [].Outer.wid;
1529 jheight = last [].Outer.ht;
1531 box with .nw at 6th last [].nw wid 6*jwidth ht jheight;
1533 # Use {} to avoid changing position from last box draw.
1534 # This is necessary so move in any direction will work as expected
1535 {"Jumpers in state $1$2$3$4$5$6" at last box .s + (0, -0.2);}
1538 # Sample macro invocations.
1539 jumperblock(1,1,0,0,1,0);
1541 jumperblock(1,0,1,0,1,1);
1549 It yields the following:
1552 # Plot a single jumper in a box, $1 is the on-off state.
1555 Outer: box invis wid 0.45 ht 1;
1557 # Count on end ] to reset these
1558 boxwid = Outer.wid * shrinkfactor / 2;
1559 boxht = Outer.ht * shrinkfactor / 2;
1561 box fill (!$1) with .s at center of Outer;
1562 box fill ($1) with .n at center of Outer;
1565 # Plot a block of six jumpers
1566 define jumperblock {
1574 jwidth = last [].Outer.wid;
1575 jheight = last [].Outer.ht;
1577 box with .nw at 6th last [].nw wid 6*jwidth ht jheight;
1579 # Use {} to avoid changing position from last box draw.
1580 # This is necessary so move in any direction will work as expected
1581 {"Jumpers in state $1$2$3$4$5$6" at last box .s + (0, -0.2);}
1584 # Sample macro invocations
1585 jumperblock(1,1,0,0,1,0);
1587 jumperblock(1,0,1,0,1,1);
1589 .CE "1: Sample use of a macro"
1591 This macro example illustrates how you can combine [], brace grouping,
1592 and variable assignment to write true functions.
1594 One detail the example above does not illustrate is the fact that
1595 macro argument parsing is not token-oriented. If you call
1596 \fBjumper(\ 1\ )\fP, the value of $1 will be \fB"\ 1\ "\fP. You could
1597 even call \fBjumper(big\ string)\fP to give $1 the value
1598 \fB"big\ string"\fP.
1600 If you want to pass in a coordinate pair, you can avoid getting
1601 tripped up by the comma by wrapping the pair in parentheses.
1603 Macros persist through pictures. To undefine a macro, say \fBundef\fP
1604 \fIname\fR; for example,
1606 \f(CWundef jumper\fP
1607 \f(CWundef jumperblock\fP
1610 would undefine the two macros in the jumper block example.
1612 Import/Export Commands
1614 Commands that import or export data between \fBpic\fR and its
1615 environment are described here.
1617 File and Table Insertion
1621 \f(CWcopy\fP \fIfilename\fR
1624 inserts the contents of \fIfilename\fR in the \fBpic\fP input stream.
1625 Any \fB.PS\fP/\fB.PE\fP pair in the file will be ignored. This, you
1626 can use this to include pre-generated images.
1628 A variant of this statement replicates the \fBcopy thru\fP feature of
1629 \fIgrap\fP(1). The call
1631 \f(CWcopy\fP \fIfilename\fR \f(CWthru\fP \fImacro\fP
1634 calls \fImacro\fP (which may be either a name or replacement text)
1635 on the arguments obtained by breaking each line of the file into
1636 blank-separated fields. The macro may have up to 9\~arguments. The
1637 replacement text may be delimited by braces or by a pair of instances
1638 of any character not appearing in the rest of the text.
1642 \f(CWcopy\fP \f(CWthru\fP \fImacro\fP
1645 omitting the filename, lines to be parsed are taken from the input
1646 source up to the next \fB.PE\fP.
1648 In either of the last two \fBcopy\fP commands, GNU \fBgpic\fP permits a
1649 trailing `\fBuntil\fP \fIword\/\fP' clause to be added which terminates
1650 the copy when the first word matches the argument (the default
1651 behavior is therefore equivalent to \fBuntil .PE\fP).
1653 Accordingly, the command
1659 copy thru % circle at ($1,$2) % until "END"
1687 The command \fBprint\fR accepts any number of arguments, concatenates
1688 their output forms, and writes the result to standard error. Each
1689 argument must be an expression, a position, or a text string.
1691 Escape to Post-Processor
1695 \fBcommand\fR \fIarg\fR\|.\|.\|.
1698 \fBpic\fP concatenates the arguments and pass them through as a line
1699 to troff or \*[tx]. Each
1701 must be an expression, a position, or text.
1702 This has a similar effect to a line beginning with
1706 but allows the values of variables to be passed through.
1708 Executing Shell Commands
1712 \f(CWsh\fP \f(CW{\fP \fIanything.\|.\|.\fP \f(CW}\fP
1715 macro-expands the text in braces, then executes it as a shell command.
1716 This could be used to generate images or data tables for later
1717 inclusion. The delimiters shown as {} here may also be two copies of
1718 any one character not present in the shell command text. In either
1719 case, the body may contain balanced {} pairs. Strings in the body
1720 may contain balanced or unbalanced braces in any case.
1722 Control-flow constructs
1724 The \fBpic\fP language provides conditionals and looping. For
1730 for i = 0 to 2 * pi by 0.1 do {
1732 "." at (i/2, sin(i)/2);
1733 ":" at (i/2, cos(i)/2);
1743 for i = 0 to 2 * pi by 0.1 do {
1745 "." at (i/2, sin(i)/2);
1746 ":" at (i/2, cos(i)/2);
1749 .CE "1: Plotting with a \fBfor\fP loop"
1751 The syntax of the \fBfor\fP statement is:
1753 \fBfor\fR \fIvariable\fR \fB=\fR \fIexpr1\/\fR \fBto\fR \fIexpr2\/\fR \
1754 [\fBby\fR [\fB*\fR]\fIexpr3\/\fR] \fBdo\fR \fIX\fR \fIbody\fR \fIX\fR
1756 The semantics are as follows: Set
1761 is less than or equal to
1771 is not given, increment
1780 will instead be multiplied by
1783 can be any character not occurring in
1784 \fIbody\fR; or the two \fIX\/\fPs may be paired braces (as in the
1787 The syntax of the \fBif\fP statement is as follows:
1789 \fBif\fR \fIexpr\fR \fBthen\fR \fIX\fR \fIif-true\fR \fIX\fR \
1790 [\fBelse\fR \fIY\fR \fIif-false\fR \fIY\/\fR]
1792 Its semantics are as follows: Evaluate
1794 if it is non-zero then do
1799 can be any character not occurring in
1802 can be any character not occurring in
1805 Eithe or both of the
1809 pairs may instead be balanced pairs of
1810 braces ({ and\~}) as in the \fBsh\fR command. In either case, the
1811 \fIif-true\fR may contain balanced pairs of braces. None of these
1812 delimiters will be seen inside strings.
1814 All the usual relational operators my be used in conditional expressions;
1815 \fB!\&\fP (logical negation, not factorial), \fB&&\fP, \fB|\||\fP, \fB==\fP,
1816 \fB!=\fP, \fB>=\fP, \fB<=\fP, \fB<\fP, \fB>\fP.
1818 String comparison is also supported using \fB==\fP and \fB!=\fP. String
1819 comparisons may need to be parenthesized to avoid syntactic
1822 Interface To [gt]roff
1824 The output of \fBpic\fP is \fB[gt]roff\fP drawing commands. The GNU
1825 \fIgpic\/\fP(1) command warns that it relies on drawing extensions
1826 present in \fIgroff\/\fP(1) that are not present in \fItroff\/\fP(1).
1830 The DWB \fIpic\/\fP(1) program will accept one or two arguments to
1831 \&\fB.PS\fP, which is interpreted as a width and height in inches to
1832 which the results of \fIpic\/\fP(1) should be scaled (width and height
1833 scale independently). If there is only one argument, it is
1834 interpreted as a width to scale the picture to, and height will be
1835 scaled by the same proportion.
1837 GNU \fBgpic\fP is less general; it will accept a single width to scale
1838 to, or a zero width and a maximum height to scale to. With
1839 two non-zero arguments, it will scale to the maximum height.
1841 How Scaling is Handled
1843 When \fBpic\fP processes a picture description on input, it passes
1844 \fB.PS\fP and \fB.PE\fP through to the postprocessor. The \fB.PS\fP
1845 gets decorated with two numeric arguments which are the X and
1846 Y\~dimensions of the picture in inches. The post-processor can use
1847 these to reserve space for the picture and center it.
1849 The \fBmgs\fP macros, for example, include the following definitions:
1858 \&.ie \e\en[.$]<2 .@error bad arguments to PS (not preprocessed with pic?)
1860 \&. ds@need (u;\e\e$1)+1v
1861 \&. in +(u;\e\en[.l]-\e\en[.i]-\e\e$2/2>?0)
1866 \&.sp \e\en[DD]u+.5m
1874 Equivalent definition will be supplied by GNU \fIpic\/\fP(1) if you use
1875 the \-mpic option; this should make it usable with macro pages other
1878 If \fB.PF\fP is used instead of \fB.PE\fP, the \fBtroff\fP position is
1879 restored to what it was at the picture start (Kernighan notes that
1880 the\~F stands for \[lq]flyback\[rq]).
1884 \&\fB.PS <\,\fP\fIfile\fP
1887 causes the contents of \fIfile\fP to replace the \fB.PS\fP line. This
1888 feature is deprecated; use `\fBcopy\fP \fIfile\fR' instead).
1890 By default, input lines that begin with a period are passed to the
1891 postprocessor, embedded at the corresponding point in the output.
1892 Messing with horizontal or vertical spacing is an obvious recipe for
1893 bugs, but point size and font changes will usually be safe.
1895 Point sizes and font changes are also safe within text strings, as
1896 long as they are undone before the end of string.
1898 The state of \fB[gt]roff\fP's fill mode is preserved across pictures.
1900 The Kernighan paper notes that there is a subtle problem with
1901 complicated equations inside \fBpic\fR pictures; they come out wrong if
1902 \fIeqn\/\fP(1) has to leave extra vertical space for the equation.
1903 If your equation involves more than subscripts and superscripts, you
1904 must add to the beginning of each equation the extra information
1905 \fBspace\~0\fP. He gives the following example:
1910 box "$space 0 {H( omega )} over {1 - H( omega )}$"
1921 box "@space 0 {H( omega )} over {1 - H( omega )}@"
1924 .CE "1: Equations within pictures"
1929 \*[tx] mode is enabled by the
1932 In \*[tx] mode, pic will define a vbox called
1935 You must yourself print that vbox using, for example, the command
1939 \ecenterline{\ebox\egraph}
1942 Actually, since the vbox has a height of zero this will produce
1943 slightly more vertical space above the picture than below it;
1947 \ecenterline{\eraise 1em\ebox\egraph}
1952 You must use a \*[tx] driver that supports the
1954 specials, version\~2.
1956 Lines beginning with
1958 are passed through transparently; a
1960 is added to the end of the line to avoid unwanted spaces.
1961 You can safely use this feature to change fonts or to
1962 change the value of \fB\ebaselineskip\fR.
1963 Anything else may well produce undesirable results; use at your own risk.
1964 Lines beginning with a period are not given any special treatment.
1966 The \*[tx] mode of \fIpic\/\fP(1) will \fInot\fP translate \fBtroff\fP
1967 font and size changes included in text strings!
1971 GNU \fIgpic\/\fP(1) has a command
1973 \fBplot\fR \fIexpr\fR [\fB"\fItext\fB"\fR]
1975 This is a text object which is constructed by using
1977 as a format string for sprintf
1982 is omitted a format string of \fB"%g"\fP is used.
1983 Attributes can be specified in the same way as for a normal text
1985 Be very careful that you specify an appropriate format string;
1986 \fBpic\fP does only very limited checking of the string.
1987 This is deprecated in favour of
1990 Some Larger Examples
1992 Here are a few larger examples, with complete source code.
1993 One of our earlier examples is generated in an instructive way using a
2001 # Draw a demonstration up left arrow with grid box overlay
2007 box wid 0.5 ht 0.5 dotted with .nw at last arrow .end;
2008 for i = 2 to ($1 / 0.5) do
2010 box wid 0.5 ht 0.5 dotted with .sw at last box .se;
2012 move down from last arrow .center;
2014 if ( $1 == boxht ) \e
2015 then { "\efBline up left\efP" } \e
2016 else { sprintf("\efBarrow up left %g\efP", $1) };
2019 move right 0.1 from last [] .e;
2034 # Draw a demonstration up left arrow with grid box overlay
2040 box wid 0.5 ht 0.5 dotted with .nw at last arrow .end;
2041 for i = 2 to ($1 / 0.5) do
2043 box wid 0.5 ht 0.5 dotted with .sw at last box .se;
2045 move down from last arrow .center;
2047 if ( $1 == boxht ) \
2048 then { "\fBline up left\fP" } \
2049 else { sprintf("\fBarrow up left %g\fP", $1) };
2052 move right 0.1 from last [] .e;
2060 .CE "1: Diagonal arrows (dotted boxes show the implied 0.5-inch grid)"
2062 Here's an example concocted to demonstrate layout of a large,
2063 multiple-part pattern:
2070 define filter {box ht 0.25 rad 0.125}
2074 box "\efBms\efR" "sources";
2076 box "\efBHTML\efR" "sources";
2078 box "\efBlinuxdoc-sgml\efP" "sources" wid 1.5;
2080 box "\efBTexinfo\efP" "sources";
2082 line down from 1st box .s lineht;
2084 line down from 2nd box .s; filter "\efBhtml2ms\efP";
2086 line down from 3rd box .s; filter "\efBformat\efP";
2088 line down from 4th box .s; filter "\efBtexi2roff\efP";
2091 move down 1 from last [] .s;
2092 Anchor: box wid 1 ht 0.75 "\efBms\efR" "intermediate" "form";
2093 arrow from Top.A.end to Anchor.nw;
2094 arrow from Top.B.end to 1/3 of the way between Anchor.nw and Anchor.ne;
2095 arrow from Top.C.end to 2/3 of the way between Anchor.nw and Anchor.ne;
2096 arrow from Top.D.end to Anchor.ne
2100 line down left then down ->;
2101 filter "\efBpic\efP";
2103 filter "\efBeqn\efP";
2105 filter "\efBtbl\efP";
2107 filter "\efBgroff\efP";
2113 line down right then down ->;
2114 A: filter dotted "\efBpic2img\efP";
2116 B: filter dotted "\efBeqn2html\efP";
2118 C: filter dotted "\efBtbl2html\efP";
2120 filter "\efBms2html\efP";
2124 # Nonexistence caption
2125 box dashed wid 1 at B + (2, 0) "These tools" "don't yet exist";
2126 line chop 0 chop 0.1 dashed from last box .nw to A.e ->;
2127 line chop 0 chop 0.1 dashed from last box .w to B.e ->;
2128 line chop 0 chop 0.1 dashed from last box .sw to C.e ->;
2138 define filter {box ht 0.25 rad 0.125}
2142 box "\fBms\fR" "sources";
2144 box "\fBHTML\fR" "sources";
2146 box "\fBlinuxdoc-sgml\fP" "sources" wid 1.5;
2148 box "\fBTexinfo\fP" "sources";
2150 line down from 1st box .s lineht;
2152 line down from 2nd box .s; filter "\fBhtml2ms\fP";
2154 line down from 3rd box .s; filter "\fBformat\fP";
2156 line down from 4th box .s; filter "\fBtexi2roff\fP";
2159 move down 1 from last [] .s;
2160 Anchor: box wid 1 ht 0.75 "\fBms\fR" "intermediate" "form";
2161 arrow from Top.A.end to Anchor.nw;
2162 arrow from Top.B.end to 1/3 of the way between Anchor.nw and Anchor.ne;
2163 arrow from Top.C.end to 2/3 of the way between Anchor.nw and Anchor.ne;
2164 arrow from Top.D.end to Anchor.ne
2168 line down left then down ->;
2175 filter "\fBgroff\fP";
2181 line down right then down ->;
2182 A: filter dotted "\fBpic2img\fP";
2184 B: filter dotted "\fBeqn2html\fP";
2186 C: filter dotted "\fBtbl2html\fP";
2188 filter "\fBms2html\fP";
2192 # Nonexistence caption
2193 box dashed wid 1 at B + (2, 0) "These tools" "don't yet exist";
2194 line chop 0 chop 0.1 dashed from last box .nw to A.e ->;
2195 line chop 0 chop 0.1 dashed from last box .w to B.e ->;
2196 line chop 0 chop 0.1 dashed from last box .sw to C.e ->;
2199 .CE "2: Hypothetical production flow for dual-mode publishing"
2205 This is an annotated grammar of \fBpic\fP.
2209 In general, \fBpic\fP is a free-format, token-oriented language that
2210 ignores whitespace outside strings. But certain lines and contructs
2211 are specially interpreted at the lexical level:
2213 A comment begins with \fB#\fP and continues to \fB\en\fP (comments may
2214 also follow text in a line). A line beginning with a period or
2215 backslash may be interpreted as text to be passed through to the
2216 post-processor, depending on command-line options. An end-of-line
2217 backslash is interpreted as a request to continue the line; the
2218 backslash and following newline are ignored.
2221 Here are the grammar terminals:
2224 .IP \s[-1]NUMBER\s[0]
2225 A floating point numeric constant. May contain a decimal point or be
2226 expressed in scientific notation in the style of \fIprintf\/\fP(3)'s %e
2227 escape. A trailing `i' or `I' (indicating the unit `inch') is ignored.
2229 A string enclosed in double quotes. A double quote within \s[-1]TEXT\s[0]
2230 must be preceded by a backslash. Instead of \s[-1]TEXT\s[0] you can use
2233 sprintf ( TEXT [, <expr> ...] )
2237 except after the `until' and `last' keywords, and after all ordinal
2238 keywords (`th' and friends).
2239 .IP \s[-1]VARIABLE\s[0]
2240 A string starting with a character from the set [a-z], optionally
2241 followed by one or more characters of the set [a-zA-Z0-9_].
2242 (Values of variables are preserved across pictures.)
2243 .IP \s[-1]LABEL\s[0]
2244 A string starting with a character from the set [A-Z], optionally
2245 followed by one or more characters of the set [a-zA-Z0-9_].
2246 .IP \s[-1]COMMAND-LINE\s[0]
2247 A line starting with a command character (`.' in groff mode, `\e' in
2249 .IP \s[-1]BALANCED-TEXT\s[0]
2250 A string either enclosed by `{' and `}' or with \fIX\fP and \fIX\fP,
2251 where \fIX\fP doesn't occur in the string.
2252 .IP \s[-1]BALANCED-BODY\s[0]
2253 Delimiters as in \s[-1]BALANCED-TEXT\s[0]; the body will be interpreted as
2254 `\fB\[la]command\[ra].\|.\|.\fP'.
2255 .IP \s[-1]FILENAME\s[0]
2256 The name of a file. This has the same semantics as \s[-1]TEXT\s[0].
2257 .IP \s[-1]MACRONAME\s[0]
2258 Either \s[-1]VARIABLE\s[0] or \s[-1]LABEL\s[0].
2263 Tokens not enclosed in \[la]\|\[ra] are literals, except:
2265 \fB\en\fP is a newline.
2267 Three dots is a suffix meaning `replace with 0 or more repetitions
2268 of the preceding element(s).
2270 An enclosure in square brackets has its usual meaning of `this clause is
2273 Square-bracket-enclosed portions within tokens are optional. Thus,
2274 `h\^[eigh]\^t' matches either `height' or `ht'.
2276 If one of these special tokens has to be referred to literally, it is
2277 surrounded with single quotes.
2279 The top-level \fBpic\fP object is a picture.
2283 .PS [NUMBER [NUMBER]]\en
2289 The arguments, if present, represent the width and height of the picture,
2290 causing \fBpic\fR to attempt to scale it to the given dimensions in
2291 inches. In no case, however, will the X and Y\~dimensions of the
2292 picture exceed the values of the style variables \fBmaxpswid\fP and
2293 \fBmaxpsheight\fP (which default to the normal 8.5\^i by 11\^i page size).
2295 If the ending `.PE' is replaced by `.PF', the page vertical position is
2296 restored to its value at the time `.PS' was encountered. Another
2297 alternate form of invocation is `.PS\ <\s[-1]FILENAME\s[0]', which
2298 replaces the `.PS' line with a file to be interpreted by \fBpic\fR (but
2299 this feature is deprecated).
2301 The `.PS', `.PE', and `.PF' macros to perform centering and scaling are
2302 normally supplied by the post-processor.
2304 In the following, either `|' or a new line starts an alternative.
2315 <primitive> [<attribute>]
2316 LABEL : [;] <command>
2317 LABEL : [;] <command> [<position>]
2319 VARIABLE [:] = <any-expr>
2320 up | down | left | right
2322 command <print-arg> ...
2323 print <print-arg> ...
2326 copy [FILENAME] thru MACRONAME [until TEXT]
2327 copy [FILENAME] thru BALANCED-BODY [until TEXT]
2328 for VARIABLE = <expr> to <expr> [by [*] <expr>] do BALANCED-BODY
2329 if <any-expr> then BALANCED-BODY [else BALANCED-BODY]
2330 reset [VARIABLE [[,] VARIABLE ...]]
2342 The current position and direction are saved on entry to a `{\ .\|.\|.\ }'
2343 construction and restored on exit from it.
2345 Note that in `if' constructions, newlines can only occur in
2346 \s[-1]BALANCED-BODY\s[0]. This means that
2356 will fail. You have to use the braces on the same line as the keywords:
2367 This restriction doesn't hold for the body after the `do' in a `for'
2374 <any-expr> <logical-op> <any-expr>
2392 Logical operators are handled specially by \fBpic\fP since they can
2393 deal with text strings also. \fBpic\fP uses \%\fIstrcmp\/\fP(3) to test
2394 for equality of strings; an empty string is considered as `false' for
2399 box \fR# closed object \[em] rectangle\fP
2400 circle \fR# closed object \[em] circle\fP
2401 ellipse \fR# closed object \[em] ellipse\fP
2402 arc \fR# open object \[em] quarter-circle\fP
2403 line \fR# open object \[em] line\fP
2404 arrow \fR# open object \[em] line with arrowhead\fP
2405 spline \fR# open object \[em] spline curve\fP
2407 TEXT TEXT ... \fR# text within invisible box\fP
2408 plot <expr> TEXT \fR# formatted text\fP
2409 '[' <command> ... ']'
2413 Drawn objects within `[\ .\|.\|.\ ]' are treated as a single composite
2414 object with a rectangular shape (that of the bounding box of all the
2415 elements). Variable and label assignments within a block are local to
2416 the block. Current direction of motion is restored to the value at start
2417 of block upon exit. Position is \fInot\fR restored (unlike `{\ }');
2418 instead, the current position becomes the exit position for the current
2419 direction on the block's bounding box.
2423 h[eigh]t <expr> \fR# set height of closed figure \fP
2424 wid[th] <expr> \fR# set width of closed figure \fP
2425 rad[ius] <expr> \fR# set radius of circle/arc \fP
2426 diam[eter] <expr> \fR# set diameter of circle/arc \fP
2427 up [<expr>] \fR# move up \fP
2428 down [<expr>] \fR# move down \fP
2429 left [<expr>] \fR# move left \fP
2430 right [<expr>] \fR# move right \fP
2431 from <position> \fR# set from position of open figure\fP
2432 to <position> \fR# set to position of open figure\fP
2433 at <position> \fR# set center of open figure\fP
2434 with <path> \fR# fix corner/named point at specified location\fP
2435 with <position> \fR# fix position of object at specified location\fP
2436 by <expr-pair> \fR# set object's attachment point\fP
2437 then \fR# sequential segment composition\fP
2438 dotted [<expr>] \fR# set dotted line style\fP
2439 dashed [<expr>] \fR# set dashed line style\fP
2440 thick[ness] <expr> \fR# set thickness of lines\fP
2441 chop [<expr>] \fR# chop end(s) of segment\fP
2442 '->' | '<-' | '<->' \fR# decorate with arrows\fP
2443 invis[ible] \fR# make primitive invisible\fP
2444 solid \fR# make closed figure solid\fP
2445 fill[ed] [<expr>] \fR# set fill density for figure\fP
2446 colo[u]r[ed] TEXT \fR# set fill and outline color for figure\fP
2447 outline[d] TEXT \fR# set outline color for figure\fP
2448 shaded TEXT \fR# set fill color for figure\fP
2449 same \fR# copy size of previous object\fP
2450 cw | ccw \fR# set orientation of curves\fP
2451 ljust | rjust \fR# adjust text horizontally\fP
2452 above | below \fR# adjust text vertically\fP
2453 aligned \fR# align parallel to object\fP
2454 TEXT TEXT ... \fR# text within object\fP
2455 <expr> \fR# motion in the current direction\fR
2459 Missing attributes are supplied from defaults; inappropriate ones are
2460 silently ignored. For lines, splines, and arcs, height and width
2461 refer to arrowhead size.
2463 The `at' primitive sets the center of the current object. The
2464 `with' attribute fixes the specified feature of the given object
2465 to a specified location. (Note that `with' is incorrectly described
2466 in the Kernighan paper.)
2468 The `by' primitive is not documented in the tutorial portion of
2469 the Kernighan paper, and should probably be considered unreliable.
2471 The primitive `arrow' is a synonym for `line\ ->'.
2473 Text is normally an attribute of some object, in which case successive
2474 strings are vertically stacked and centered on the object's center by
2475 default. Standalone text is treated as though placed in an invisible
2478 A text item consists of a string or sprintf-expression, optionally
2479 followed by positioning information. Text (or strings specified with
2480 `sprintf' may contain [gtn]roff font changes, size changes, and local
2481 motions, provided those changes are undone before the end of the current
2484 A position is an (x,y) coordinate pair. There are lots of different
2485 ways to specify positions:
2489 <position-not-place>
2495 <position-not-place> ::=
2497 <position> + <expr-pair>
2498 <position> - <expr-pair>
2499 ( <position> , <position> )
2500 <expr> [of the way] between <position> and <position>
2501 <expr> '<' <position> , <position> '>'
2516 <corner> [of] <label>
2531 .ne | .se | .nw | .sw
2532 .c[enter] | .start | .end
2533 .t[op] | .b[ot[tom]] | .l[eft] | .r[ight]
2534 left | right | <top-of> | <bottom-of>
2535 <north-of> | <south-of> | <east-of> | <west-of>
2536 <center-of> | <start-of> | <end-of>
2537 upper left | lower left | upper right | lower right
2543 xxx \fR# followed by `of'\fP
2549 <ordinal> <object-type>
2550 [<ordinal>] last <object-type>
2557 INT st | INT nd | INT rd
2576 As Kernighan notes, \[lq]since barbarisms like \fB1th\fP and \fB3th\fP are
2577 barbaric, synonyms like \fB1st\fP and \fB3rd\fP are accepted as well.\[rq]
2578 Objects of a given type are numbered from 1 upwards in order of
2579 declaration; the \fBlast\fP modifier counts backwards.
2581 The \[lq]'th\[rq] form (which allows you to select a previous object with
2582 an expression, as opposed to a numeric literal) is not documented in DWB's
2585 The \[la]\|\fIxxx\fP-of\|\[ra] rule is special: The lexical parser checks whether
2586 \fIxxx\fP is followed by the token `of' without eliminating it so that
2587 the grammar parser can still see `of'. Valid examples of specifying a
2588 place with corner and label are thus
2605 both cause a syntax error. (DWB \fBpic\fP also allows the weird form
2608 Here the special rules for the `with' keyword using a path:
2613 ( <relative-path> , <relative-path> )
2620 . LABEL [. LABEL ...] [<corner>]
2624 The following style variables control output:
2626 center tab(@), linesize(2);
2630 Style Variable@Default@What It Does
2635 boxht@0.5@Default height of a box
2636 boxwid@0.75@Default height of a box
2637 lineht@0.5@Default length of vertical line
2638 linewid@0.75@Default length of horizontal line
2639 arcrad @0.25@Default radius of an arc
2640 circlerad@0.25@Default radius of a circle
2641 ellipseht@0.5@Default height of an ellipse
2642 ellipsewid@0.75@Default width of an ellipse
2643 moveht@0.5@Default length of vertical move
2644 movewid@0.75@Default length of horizontal move
2645 textht@0@Default height of box enclosing a text object
2646 textwid@0@Default width of box enclosing a text object
2647 arrowht@0.1@Length of arrowhead along shaft
2648 arrowwid@0.05@Width of rear of arrowhead
2649 arrowhead@1@Enable/disable arrowhead filling
2650 dashwid@0.05@Interval for dashed lines
2651 maxpswid@11@Maximum width of picture
2652 maxpsht@8.5@Maximum height of picture
2653 scale@1@Unit scale factor
2654 fillval@0.5@Default fill value
2658 Any of these can be set by assignment, or reset using the \fBreset\fP
2659 statement. Style variables assigned within `[\ ]' blocks are restored to
2660 their beginning-of-block value on exit; top-level assignments persist
2661 across pictures. Dimensions are divided by \fBscale\fR on output.
2663 All \fBpic\fP expressions are evaluated in floating point; units
2664 are always inches (a trailing `i' or `I' is ignored). Expressions have
2665 the following simple grammar, with semantics very similar to
2672 <place> <place-attribute>
2677 <func1> ( <any-expr> )
2678 <func2> ( <any-expr> , <any-expr> )
2685 .x | .y | .h[eigh]t | .wid[th] | .rad
2691 + | - | * | / | % | ^ | '<' | '>' | '<=' | '>='
2697 sin | cos | log | exp | sqrt | int | rand | srand
2707 Both \fBexp\fP and \fBlog\fP are base 10; \fBint\fP does integer
2708 truncation; and \fBrand()\fP returns a random number in [0-1).
2710 There are \fBdefine\fP and \fBundef\fR statements which are not part
2711 of the grammar (they behave as pre-processor macros to the language).
2712 These may be used to define pseudo-functions.
2715 \fBdefine\fP \fIname\fP \fB{\fP \fIreplacement-text\fP \fB}\fP
2719 This defines \fIname\fR as a macro to be replaced by the replacement
2720 text (not including the braces). The macro may be called as
2723 \fIname\/\fB(\,\fIarg1, arg2, .\|.\|., argn\fB\/)\fR
2727 The arguments (if any) will be substituted for tokens $1, $2 .\|.\|.\& $n
2728 appearing in the replacement text. To undefine a macro, say \fBundef\fP
2729 \fIname\fR, specifying the name to be undefined.
2732 History and Acknowledgements
2734 Original \fBpic\fP was written to go with Joseph Ossanna's original
2735 \fItroff\/\fP(1) by Brian Kernighan, and later re-written by Kernighan
2736 with substantial enhancements (apparently as part of the evolution of
2737 \fItroff\/\fP(1) into \fIditroff\/\fP(1) to generate
2738 device-independent output).
2740 The language had been inspired by some earlier graphics languages
2741 including \fBideal\fP and \fBgrap\fP. Kernighan credits Chris van Wyk
2742 (the designer of \fBideal\fP) with many of the ideas that went into
2745 .\" the original definitions of EQ and EN cause insertion of vertical
2746 .\" space which is not appropriate here
2754 The \fBpic\fP language was originally described by Brian Kernighan in
2755 Bell Labs Computing Science Technical Report #116 (you can obtain a
2756 PostScript copy of the revised version, [1], by sending a mail message to
2757 \fInetlib@research.att.com\fP with a body of `send 116 from
2758 research/cstr'). There have been two revisions, in 1984 and 1991.
2760 The document you are reading effectively subsumes Kernighan's
2761 description; it was written to fill in lacun\[ae] in the exposition and
2762 integrate in descriptions of the GNU \fIgpic\/\fP(1) features.
2764 The GNU \fBgpic\fR implementation was written by James Clark
2765 \[la]\,\fIjjc@jclark.com\/\fP\[ra]. It is currently maintained by Werner
2766 Lemberg \[la]\,\fIwl@gnu.org\/\fP\[ra].
2770 Kernighan, B. W. \fBPIC \[em] A Graphics Language for Typesetting
2771 (Revised User Manual)\fP. Bell Labs Computing Science Technical Report
2772 #116, December 1991.
2774 Van Wyk, C. J. \fBA high-level language for specifying pictures\fP.
2775 \fIACM Transactions On Graphics\fP 1,2 (1982) 163-182.