PIC(1)

NAME
pic - troff preprocessor for drawing pictures

SYNOPSIS
pic [-SU] [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.

Arbitrary whitespace can be inserted between the dot and the token PS, PE or PF. Macros with these names are ignored by pic if "'" is used instead of ".".

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 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.

The -S command line option will disable execution of `sh' command elements. -U reverts the effect of a previous -S.

SEE ALSO
grap(1), troff(1)
B. W. Kernighan, ``PIC—a Graphics Language for Typesetting'', Unix Research System Programmer's Manual, Tenth Edition, Volume 2