pic, tpic, svgpic – troff and tex preprocessors for drawing pictures

pic [ files ]
tpic [ files ]
svgpic [ files ]

Pic is a troff(1) preprocessor for drawing figures on a typesetter. Pic code is contained between .PS and .PE lines:
.PS optional-width optional-height
or in a file mentioned in a .PS line:
.PS <file
If optional-width is present, the picture is made that many inches wide, regardless of any dimensions used internally. The height is scaled in the same proportion unless optional-height is present. If .PF is used instead of .PE, the typesetting position after printing is restored to what it was upon entry.
An element-list is a list of elements:
primitive attribute-list
: element
: position
= expr
{ element-list }
element-list ]
var = expr to expr by expr do { anything }
expr then { anything } else { anything }
file, copy thru macro, copy file thru macro
sh { commandline }
reset optional var-list
Elements are separated by newlines or semicolons; a long element may be continued by ending the line with a backslash. Comments are introduced by a # and terminated by a newline. Variable names begin with a lower case letter; place names begin with upper case. Place and variable names retain their values from one picture to the next.
After each primitive the current position moves in the current direction (up,down, left,right (default)) by the size of the primitive. The current position and direction are saved upon entry to a {...} block and restored upon exit. Elements within a block enclosed in [...] are treated as a unit; the dimensions are determined by the extreme points of the contained objects. Names, variables, and direction of motion within a block are local to that block.
Troff-command is any line that begins with a period. Such a line is assumed to make sense in the context where it appears; generally, this means only size and font changes.
The primitive objects are:
box    circle    ellipse    arc    line    arrow    spline    move    text-list
arrow is a synonym for line −>.
An attribute-list is a sequence of zero or more attributes; each attribute consists of a keyword, perhaps followed by a value.
h(eigh)t expr             wid(th) expr
rad(ius) expr             diam(eter) expr
up opt-expr               down opt-expr
right opt-expr             left opt-expr
from position              to position
at position                with corner
by expr, expr              then
opt-expr            dashed opt-expr
chop opt-expr              −>    <−    <−>
invis                  same
text-list                  expr
Missing attributes and values are filled in from defaults. Not all attributes make sense for all primitives; irrelevant ones are silently ignored. The attribute at causes the geometrical center to be put at the specified place; with causes the position on the object to be put at the specified place. For lines, splines and arcs, height and width refer to arrowhead size. A bare expr implies motion in the current direction.
Text is normally an attribute of some primitive; by default it is placed at the geometrical center of the object. Stand-alone text is also permitted. A text list is a list of text items:
positioning ...
sprintf("format", expr, ...) positioning ...
center    ljust    rjust    above    below
If there are multiple text items for some primitive, they are arranged vertically and centered except as qualified. Positioning requests apply to each item independently. Text items may contain troff commands for size and font changes, local motions, etc., but make sure that these are balanced so that the entering state is restored before exiting.
A position is ultimately an x,y coordinate pair, but it may be specified in other ways.
expr, expr
± expr, expr
± ( expr, expr )
position, position )          x from one, y the other
expr [of the way] between position and position
< position , position >
( position )
placename optional-corner
of placename
nth primitive optional-corner
of nth primitive
An optional-corner is one of the eight compass points or the center or the start or end of a primitive.
.n    .e    .w    .s    .ne    .se    .nw    .sw    .c    .start    .end
top    bot    left    right    start    end
Each object in a picture has an ordinal number; nth refers to this.
nth,    nth last
The built-in variables and their default values are:
boxwid 0.75              boxht 0.5
circlerad 0.25            arcrad 0.25
ellipsewid 0.75           ellipseht 0.5
linewid 0.5              lineht 0.5
movewid 0.5              moveht 0.5
textwid 0               textht 0
arrowwid 0.05            arrowht 0.1
dashwid 0.1              arrowhead 2
scale 1
These may be changed at any time, and the new values remain in force from picture to picture until changed again or reset by a reset statement. Variables changed within [ and ] revert to their previous value upon exit from the block. Dimensions are divided by scale during output.
Expressions in pic are evaluated in floating point. All numbers representing dimensions are taken to be in inches.
expr op expr
! expr
( expr )
place .x    place .y    place .ht    place .wid    place .rad
expr)    cos(expr)    atan2(expr,expr)    log(expr)    exp(expr)
expr)    max(expr,expr)    min(expr,expr)    int(expr)    rand()
+    −    *    /    %    <    <=    >    >=    ==    !=    &&    ||
The define and undef statements are not part of the grammar.
define name { replacement text }
Occurrences of $1, $2, etc., in the replacement text will be replaced by the corresponding arguments if name is invoked as
name(arg1, arg2, ...)
Non-existent arguments are replaced by null strings. Replacement text may contain newlines. The undef statement removes the definition of a macro.
Tpic is a tex(1) preprocessor that accepts pic language. It produces Tex commands that define a box called \graph, which contains the picture. The box may be output this way:
Svgpic accepts pic language and produces a Scalable Vector Graphics (SVG) image suitable for use in HTML documents.

arrow "input" above; box "process"; arrow "output" above
A: ellipse
circle rad .1 with .w at A.e
circle rad .05 at 0.5 <A.c, A.ne>
circle rad .065 at 0.5 <A.c, A.ne>
spline from last circle.nw left .25 then left .05 down .05
arc from A.c to A.se rad 0.5
for i = 1 to 10 do { line from A.s+.025*i,.01*i down i/50 }
arrow "input" above; box "process"; arrow "output" above move A: ellipse
circle rad .1 with .w at A.e
circle rad .05 at 0.5 <A.c, A.ne>
circle rad .065 at 0.5 <A.c, A.ne>
spline from last circle.nw left .25 then left .05 down .05
arc from A.c to A.se rad 0.5
for i = 1 to 10 do { line from A.s+.025*i,.01*i down i/50 }


grap(1), doctype(1), troff(1)
B. W. Kernighan, “PIC--a Graphics Language for Typesetting”, Unix Research System Programmer’s Manual, Tenth Edition, Volume 2

Svgpic is only lightly tested. It should handle troff commands in text output.

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