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

SYNOPSIS
pic [ files ]

tpic [ files ]

DESCRIPTION
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
element–list
.PE

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
placename
: element
placename
: position
var
= expr
direction
{ element–list }
[
element–list ]
for
var = expr to expr by expr do { anything }
if
expr then { anything } else { anything }
copy
file,    copy thru macro,    copy file thru macro
sh { commandline }
print
expr
reset optional var–list
troff–command

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
dotted
opt–expr          dashed opt–expr
chop opt–expr            –>    <–    <–>
invis                  same
fill
opt–expr
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:
text–item:
"
..."
positioning ...
sprintf("format", expr, ...) positioning ...
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.
position:
expr, expr
place ±
expr, expr
place ±
( expr, expr )
(
position, position )        x from one, y the other
expr [of the way] between position and position
expr <
position , position >
( position )

place:
placename optional–corner
corner
of placename
nth primitive optional–corner
corner
of nth primitive
Here
An optional–corner is one of the eight compass points or the center or the start or end of a primitive.
optional–corner:
.n    .e    .w    .s    .ne    .se    .nw    .sw    .c    .start    .end
corner:
top    bot    left    right    start    end
Each object in a picture has an ordinal number; nth refers to this.
nth:
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:
expr op expr
expr
! expr
( expr )
variable
number
place .x    place .y    place .ht    place .wid    place .rad
sin(
expr)    cos(expr)    atan2(expr,expr)    log(expr)    exp(expr)
sqrt(
expr)    max(expr,expr)    min(expr,expr)    int(expr)    rand()
op:
+    –    *    /    %    <    <=    >    >=    ==    !=    &&    ||

The define and undef statements are not part of the grammar.
define name { replacement text }
undef
name
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:
\centerline{\box\graph}

EXAMPLES
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 }

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 }

SOURCE
/sys/src/cmd/pic

SEE ALSO
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