pic

TeX mode

TeX-compatible output is produced when the -t option is specified. You must use a TeX driver that supports tpic version 2 specials. (tpic was a fork of AT&T pic by Tim Morgan of the University of California at Irvine that diverged from its source around 1984. It is best known today for lending its name to a group of \special commands it produced for TeX.)

Lines beginning with \ are passed through unaltered except for a % suffix to avoid unwanted spaces. Use this feature to change fonts or the value of \baselineskip. Other applications may produce undesirable results; use at your own risk. By default, lines beginning with a dot are not treated specially—but see the -c option.

In TeX mode, pic defines a vbox called \graph for each picture. Use GNU pic's figname command to change the name of the vbox. You must print that vbox yourself using the command

\centerline{\box\graph}

\centerline{\raise 1em\box\graph}

\def\gpicbox#1{%
  \vbox{\unvbox\csname #1\endcsname\kern 0pt}}

Commands

Several commands new to GNU pic accept delimiters, shown in their synopses as braces { }. Nesting of braces is supported. Any other characters (except a space, tab, or newline) may be used as alternative delimiters, in which case the members of a given pair must be identical. GNU pic recognizes double-quoted strings within delimiters of either kind; such strings may contain the delimiter character or unbalanced braces.

for variable = expr1 to expr2 [by [*]expr3] do X body X

Set variable to expr1. While the value of variable is less than or equal to expr2, do body and increment variable by expr3; if by is not given, increment variable by 1. expr3 can be negative, in which case variable is then tested whether it is greater than or equal to expr2. A * prefix on variable multiplies it by expr3 (which must be greater than zero) at each iteration rather than incrementing it. If the range constraint on expr3 isn't met, the loop does not execute. X can be any character not in body.

if expr then X if-true X [else Y if-false Y]

Evaluate expr; if it is non-zero then do if-true, otherwise do if-false. X can be any character not in if-true. Y can be any character not in if-false.

print arg ...

Catenate and write arguments to the standard error stream followed by a newline. Each arg must be an expression, a position, or text. This feature is useful for debugging.

command arg ...

.PS
x = 14
command ".ds string x is " x "."
.PE
\*[string]

x is 14.

sh X command X

Pass command to a shell via system(3). Ignored if -U option not specified.

copy "filename"

Include filename at this point in the file.

copy ["filename"] thru X body X [until "word"]

copy ["filename"] thru macro [until "word"]

.PS
copy thru % circle at ($1,$2) % until "END"
1 2
3 4
5 6
END
box
.PE

.PS
circle at (1,2)
circle at (3,4)
circle at (5,6)
box
.PE

reset

reset pvar1[,] pvar2 ...

Reset predefined variables pvar1, pvar2 ... to their default values; if no arguments are given, reset all predefined variables to their default values. Variable names may be separated by commas, spaces, or both. Assigning a value to scale also causes all predefined variables that control dimensions to be reset to their default values times the new value of scale.

plot expr ["text"]

Create a text object by using text as a format string for sprintf(3) with an argument of expr. If text is omitted, "%g" is implied. Attributes can be specified in the same way as for a normal text object. Caution: be very careful that you specify an appropriate format string in text; pic's validation of it is limited. plot is deprecated in favour of sprintf.

var := expr

.PS
x = 3
y = 3
[
x := 5
y = 5
]
print x   y
.PE

5 3

Expressions

The syntax for expressions has been significantly extended.

x ^ y (exponentiation)
sin(x)
cos(x)
atan2(y, x)
log(x) (base 10)
exp(x) (base 10, i.e. 10^x)
sqrt(x)
int(x)
rand() (return a random number between 0 and 1)
rand(x) (return a random number between 1 and x; deprecated)
srand(x) (set the random number seed)
max(e1, e2)
min(e1, e2)
!e
e1 && e2
e1 || e2
e1 == e2
e1 != e2
e1 >= e2
e1 > e2
e1 <= e2
e1 < e2
"str1" == "str2"
"str1" != "str2"

String comparison expressions must be parenthesised in some contexts to avoid ambiguity.

Other changes

A bare expression, expr, is acceptable as an attribute; it is equivalent to “dir expr”, where dir is the current direction. For example, “line 2i” draws a line 2 inches long in the current direction. The ‘i’ (or ‘I’) character is ignored; to use another measurement unit, set the scale variable to an appropriate value.

The maximum width and height of the picture are taken from the variables maxpswid and maxpsht. Initially, these have values 8.5 and 11, respectively.

Scientific notation is allowed for numbers, as with “x = 5e-2”.

Text attributes can be compounded. For example, “"foo" above ljust” is valid.

There is no limit to the depth to which blocks can be nested. For example,

[A: [B: [C: box ]]] with .A.B.C.sw at 1,2
circle at last [].A.B.C

Arcs have compass points determined by the circle of which the arc is a part.

Circles, ellipses, and arcs can be dotted or dashed. In TeX mode, splines can be dotted or dashed as well.

Boxes can have rounded corners. The rad attribute specifies the radius of the quarter-circles at each corner. If no rad or diam attribute is given, a radius of boxrad is used. Initially, boxrad has a value of 0. A box with rounded corners can be dotted or dashed.

Boxes can have slanted sides, generalizing them from rectangles to parallelograms. The xslanted and yslanted attributes specify the x and y offsets of the box's upper right corner from its default position.

The .PS line accepts a second argument specifying a maximum height for the picture. If a width of zero is specified, it is ignored when computing the scaling factor for the picture. GNU pic always scales a picture by the same amount vertically and horizontally. This differs from DWB 2.0 pic, which may change the picture's aspect ratio if a height is specified.

Each text object has an associated invisible box that determines its compass points and implicit motion. The dimensions of the box are taken from its width and height attributes. If the width attribute is not supplied, the value of textwid is assumed. If the height attribute is not supplied, the height defaults to the number of text strings associated with the object times textht. Initially, textwid and textht have values of 0.

In (almost all) places where a quoted text string can be used, an expression of the form

sprintf("format", arg, ...)

can be used instead; it transforms its arguments per format, which should be a string as described in printf(3), and appropriate to the quantity of arguments supplied. GNU pic supports only the conversion specifiers e, E, f, g, G, and %, modifiers “#”, “-”, “+”, and “ ” [space]), a minimum field width, and an optional precision.

The thickness of the lines used to draw objects is controlled by the linethick variable, which is measured in points. A negative value indicates the default thickness. In TeX output mode when the -c option is not given, this means 8 milliinches. In troff and TeX -c output modes, the default thickness corresponds to the type size. (Thus, if the type size is 10 points, a line is 10 points thick.) A linethick value of zero draws the thinnest possible line supported by the output device. Initially, linethick has a value of -1. A thick[ness] attribute is also available. For example, “circle thickness 1.5” draws a circle with a line thickness of 1.5 points. The thickness of lines is not affected by the value of the scale variable, nor by the width or height given in the .PS line.

Boxes (including boxes with rounded corners or slanted sides), circles, and ellipses can be filled by giving them an attribute of fill[ed], which takes an optional expression argument with a value between 0 and 1; 0 fills it with white, 1 with black, and values in between with a proportionally gray shade. A value greater than 1 is interpreted as the shade of gray that is being used for text and lines. Normally this is black, but output devices may provide a mechanism for changing this. Without an argument, the value of the variable fillval is used. Initially, fillval has a value of 0.5. The invisible attribute does not affect the filling of objects. Text associated with a filled object is added after the object is filled, so that the text is not obscured by the filling.

Additional modifiers are available to draw colored objects: outline[d] sets the color of the outline, shaded the fill color, and colo[u]r[ed] sets both. All expect a subsequent string argument specifying the color.

circle shaded "green" outline "black"

To change the name of the vbox in TeX mode, set the pseudo-variable figname (which is actually a specially parsed command) within a picture. For example,

.PS
figname = foobar;
circle "dig here";
.PE

Arrow heads are drawn as solid triangles if the variable arrowhead is non-zero and either TeX mode is enabled or the -n option is not used. Initially, arrowhead has a value of 1. Solid arrow heads are always filled with the current outline (stroke) color.

The troff output of pic is device-independent. The -T option is therefore redundant. Except where noted, all measurements and dimensions use inches implicitly; they are never interpreted as troff basic units.

Objects can have an aligned attribute, but it is supported only by the grops(1) and gropdf(1) output drivers. Any text associated with an aligned object is rotated about the object's center such that it is oriented along a line connecting the start and end points of the object. aligned has no effect on objects whose start and end points are coincident.

In places where nth is allowed, `expr'th is also allowed. “'th” is a single token: no space is allowed between the apostrophe and the “th”. Consider the following example.

for i = 1 to 4 do {
   box
   move right 0.5
}
for i = 1 to 3 do {
   arrow from `i'th box.ne to `i+1'th box.sw
}
    

Arbitrary polygons can be drawn using the polygon keyword followed by a series of n-1 line segments, where n is the number of edges of the polygon. This allows GNU troff to interpret the line segments as a complete object such that the filled and shaded attributes may be used. The last user-specified line segment determines the polygon's final drawing position and direction. For example, draw and fill a triangle with the following.

polygon up 1 then right 1 down 0.5 fill 0.5

Two reference point suffixes permit the positioning of drawing elements relative to a polygon. “.vertex expr” locates the vertices, and “.midpoint expr” for locating the midpoints of edges. GNU pic numbers vertices and midpoints in drawing order starting from 1 . You can abbreviate .vertex as .v or .ver, and .midpoint as .mid.

For example,

arrow down
polygon up 0.5 right 1 \
then down 0.5 right 1 \
then down 0.5 left 1 \
with .v2 at last line.end
arrow down from last polygon.v4
    

creates and correctly places a flowchart decision diamond.

.center (.c) is also available, but compass points do not work as expected and should not be used with polygons.

Converting pic to other image formats

To create a stand-alone graphics file from a pic file, first compose the picture. Bracket your pic code with .PS and .PE tokens. groff requests that don't produce formatted output may precede .PS, but format no text, not even any injected by a macro package, which may include a page number even on the first page, as mm does by default. Consider writing a “raw” roff document that uses no macro package.

Next, convert the roff/pic input into the desired format. groff distributes a simple utility, pic2graph(1), for this purpose. Other possibilities exist, particularly if you first transform your picture into PostScript format with “groff -T ps”. However, such a PostScript file lacks bounding box information; roff formatters produce page-sized output. Several tools with names beginning “psto” or “ps2” exist that can infer the bounding box and perform a format conversion. One of these is the PostScript interpreter Ghostscript (gs(1)), which exposes format converters via its -sDEVICE= option. “gs --help” lists available devices.

Alternatively, produce a PDF with “groff -T pdf”; gropdf(1)'s -p option sets the MediaBox of the file.

The Encapsulated PostScript File (EPS) format is still sometimes seen. The aforementioned Ghostscript offers ps2epsi(1), and a standalone package and command ps2eps(1) is also available.

For raster image formats, use pstopnm(1); the resulting pnm(5) file can be then converted to virtually any image format using the netpbm tools.

GNU plotutils offers a pic2plot(1) utility for converting pic input to a wide variety of other image formats, including SVG.