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%pic

Section: User Commands (1)
Updated: 2 July 2023
Index Return to Main Contents

Name

pic - compile pictures for troff or TeX
.nr d-fallback 1
.nr d-fallback 1

Synopsis

[-CnSU] [file~...] -t [-cCSUz] [file~...] --help -v --version

Description

The GNU implementation of pic is part of the document formatting system. pic is a preprocessor that translates descriptions of diagrammatic pictures embedded in or tx] input files into the language understood by tx] or troff. It copies the contents of each file to the standard output stream, except that lines between .PS and any of .PE, .PF, or .PY are interpreted as picture descriptions in the pic language. End a pic picture with .PE to leave the drawing position at the bottom of the picture, and with .PF or .PY to leave it at the top. Normally, pic is not executed directly by the user, but invoked by specifying the -p option to If no file operands are given on the command line, or if file is [lq]-[rq], the standard input stream is read. It is the user's responsibility to provide appropriate definitions of the PS, PE, and one or both of the PF and PY macros. When a macro package does not supply these, obtain simple definitions with the groff option -mpic; these will center each picture. GNU pic supports PY as a synonym of PF to work around a name space collision with the mm macro package, which defines PF as a page footer management macro. Use PF preferentially unless a similar problem faces your document.

Options

--help displays a usage message, while -v and --version show version information; all exit afterward.

-c: Be more compatible with tpic; implies -t. Lines beginning with [rs] are not passed through transparently. Lines beginning with . are passed through with the initial . changed to [rs]. A line beginning with .ps is given special treatment: it takes an optional integer argument specifying the line thickness (pen size) in milliinches; a missing argument restores the previous line thickness; the default line thickness is 8~milliinches. The line thickness thus specified takes effect only when a no-negative line thickness has not been specified by use of the thickness attribute or by setting the linethick variable.
-C: Recognize .PS, .PE, .PF, and .PY even when followed by a character other than space or newline.
-n: Don't use groff extensions to the troff drawing commands. Specify this option if a postprocessor you're using doesn't support these extensions, described in This option also causes pic not to use zer-length lines to draw dots in troff mode.
-S: Operate in safer mode; sh commands are ignored. This mode, enabled by default, can be useful when operating on untrustworthy input.
-t: Produce tx] output.
-U: Operate in unsafe mode; sh commands are interpreted.
-z: In tx] mode, draw dots using zer-length lines. The following options supported by other versions of pic are ignored.
-D: Draw all lines using the [rs]D escape sequence. GNU pic always does this.
-T~dev: Generate output for the troff device dev. This is unnecessary because the troff output generated by GNU pic is devic-independent.

Usage

This section primarily discusses the differences between GNU pic and the Eighth Edition Research Unix version of AT&T pic (1985). Many of these differences also apply to later versions of AT&T pic.

tx] mode

tx-compatible output is produced when the -t option is specified. You must use a tx] 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 [rs]special commands it produced for tx].) Lines beginning with [rs] are passed through transparently; a % is added to the end of the line to avoid unwanted spaces. You can safely use this feature to change fonts or the value of [rs]baselineskip. Anything else may well produce undesirable results; use at your own risk. By default, lines beginning with a dot are not treated specially[em]but see the -c option. In tx] mode, pic will define a vbox called [rs]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

: [rs]centerline{[rs]box[rs]graph}

for instance. Since the vbox has a height of zero (it is defined with [rs]vtop) this will produce slightly more vertical space above the picture than below it;

: [rs]centerline{[rs]raise 1em[rs]box[rs]graph}

would avoid this. To give the vbox a positive height and a depth of zero (as used by lx]'s graphics.sty, for example) define the following macro in your document.

: [rs]def[rs]gpicbox#1{%
[rs]vbox{[rs]unvbox[rs]csname #1[rs]endcsname[rs]kern 0pt}}

You can then simply say [rs]gpicbox{graph} instead of [rs]box[rs]graph.

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. Strings are recognized within delimiters of either kind; they 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. If expr3 is prefixed by * then variable will instead be multiplied by expr3. The value of expr3 can be negative for the additive case; variable is then tested whether it is greater than or equal to expr2. For the multiplicative case, expr3 must be greater than zero. If the constraints aren't met, the loop isn't executed. X can be any character not occurring in body.

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

Evaluate expr; if it is no-zero then do i-true, otherwise do i-false. X can be any character not occurring in i-true. Y can be any character not occurring in i-false.

print~arg

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

command~arg

~...

Concatenate arguments and pass them as a line to troff or tx]. Each arg must be an expression, a position, or text. command allows the values of pic variables to be passed to the formatter. For example,

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

produces

: x is 14.

when formatted with troff.

sh X command X

Pass command to a shell.

copy ",filename/"

Include filename at this point in the file.

copy~[[dq]

filename[dq]]~thru~X body X~[until~[dq]word[dq]] copy~[[dq]filename[dq]]~thru~macro~[until~[dq]word[dq]]

This construct does body once for each line of filename; the line is split into blan-delimited words, and occurrences of $i in body, for i between 1 and 9, are replaced by the i-th word of the line. If filename is not given, lines are taken from the current input up to .PE. If an until clause is specified, lines will be read only until a line the first word of which is word; that line will then be discarded. X can be any character not occurring in body. For example,

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

and

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

are equivalent. The commands to be performed for each line can also be taken from a macro defined earlier by giving the name of the macro as the argument to thru. The argument after thru is looked up as a macro name first; if not defined, its first character is interpreted as a delimiter.

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"]

This is a text object which is constructed by using text as a format string for sprintf with an argument of expr. If text is omitted a format string of [dq]%g[dq] is used. Attributes can be specified in the same way as for a normal text object. Be very careful that you specify an appropriate format string; pic does only very limited checking of the string. This is deprecated in favour of sprintf.

var~:=~expr

This syntax resembles variable assignment with = except that var must already be defined, and expr will be assigned to var without creating a variable local to the current block. (By contrast, = defines var in the current block if it is not already defined there, and then changes the value in the current block only.) For example,

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

writes

: 5 3

to the standard error stream.

Expressions

The syntax for expressions has been significantly extended. x [ha] y (exponentiation)
sin(x)
cos(x)
atan2(y, x)
log(x) (base 10)
exp(x) (base 10, i.e. 10[ha]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

means draw a line 2 inches long in the current direction. The [oq]i[cq] (or [oq]I[cq]) 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.

Scientific notation is allowed for numbers. For example

: 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 examined. For example,

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

is acceptable.

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

Circles, ellipses, and arcs can be dotted or dashed. In tx] mode splines can be dotted or dashed also.

Boxes can have rounded corners. The rad attribute specifies the radius of the quarte-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. This effectively changes the shape of a box from a rectangle to an arbitrary parallelogram. The xslanted and yslanted attributes specify the x and y~offset of the box's upper right corner from its default position.

The .PS line can have a second argument specifying a maximum height for the picture. If the width of zero is specified the width will be ignored in computing the scaling factor for the picture. GNU pic will always scale a picture by the same amount vertically as well as horizontally. This is different from DWB 2.0 pic which may scale a picture by a different amount vertically than horizontally if a height is specified.

Each text object has an invisible box associated with it. The compass points of a text object are determined by this box. The implicit motion associated with the object is also determined by this box. The dimensions of this box are taken from the width and height attributes; if the width attribute is not supplied then the width will be taken to be textwid; if the height attribute is not supplied then the height will be taken to be the number of text strings associated with the object times textht. Initially, textwid and textht have a value of 0.

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

: sprintf([dq]format[dq],~arg,~...)

can also be used; this will produce the arguments formatted according to format, which should be a string as described in appropriate for the number of arguments supplied. Only the modifiers [lq]#[rq], [lq]-[rq], [lq]+[rq], and [lq]~[rq] [space]), a minimum field width, an optional precision, and the conversion specifiers %e, %E, %f, %g, %G, and %% are supported.

The thickness of the lines used to draw objects is controlled by the linethick variable. This gives the thickness of lines in points. A negative value means use the default thickness: in tx] output mode, this means use a thickness of 8 milliinches; in tx] output mode with the -c option, this means use the line thickness specified by .ps lines; in troff output mode, this means use a thickness proportional to the pointsize. A zero value means draw the thinnest possible line supported by the output device. Initially, it has a value of -1. There is also a thick[ness] attribute. For example,

: circle thickness 1.5

would draw a circle using a line with a 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]. This takes an optional argument of an expression with a value between 0 and 1; 0 will fill it with white, 1 with black, values in between with a proportionally gray shade. A value greater than 1 can also be used: this means fill with the shade of gray that is currently being used for text and lines. Normally this will be black, but output devices may provide a mechanism for changing this. Without an argument, then the value of the variable fillval will be used. Initially, this has a value of 0.5. The invisible attribute does not affect the filling of objects. Any text associated with a filled object will be added after the object has been filled, so that the text will not be 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 [dq]green[dq] outline [dq]black[dq]

Color is not yet supported in tx] mode. Device macro files like ps.tmac declare color names; you can define additional ones with the defcolor request (see

To change the name of the vbox in tx] mode, set the pseud-variable figname (which is actually a specially parsed command) within a picture. Example:

: .PS
figname = foobar;
...
.PE

The picture is then available in the box [rs]foobar.

pic assumes that at the beginning of a picture both glyph and fill color are set to the default value.

Arrow heads will be drawn as solid triangles if the variable arrowhead is no-zero and either tx] mode is enabled or the -n option has not been given. Initially, arrowhead has a value of 1. Solid arrow heads are always filled with the current outline color.

The troff output of pic is devic-independent. The -T option is therefore redundant. All numbers are taken to be in inches; numbers are never interpreted to be in troff machine units.

Objects can have an aligned attribute. This will only work if the postprocessor is or Any text associated with an object having the aligned attribute will be rotated about the center of the object so that it is aligned in the direction from the start point to the end point of the object. This attribute will have no effect on objects whose start and end points are coincident.

In places where nth is allowed, [aq]expr[aq]th is also allowed. [lq][aq]th[lq] is a single token: no space is allowed between the apostrophe and the [lq]th[rq]. For example,

: for i = 1 to 4 do {
line from [aq]i[aq]th box.nw to [aq]i+1[aq]th box.se }

Conversion

To obtain a stan-alone picture from a pic file, enclose your pic code with .PS and .PE requests; roff configuration commands may be added at the beginning of the file, but no roff text.

It is necessary to feed this file into groff without adding any page information, so you must check which .PS and .PE requests are actually called. For example, the mm macro package adds a page number, which is very annoying. At the moment, calling standard groff without any macro package works. Alternatively, you can define your own requests, e.g., to do nothing:

: .de PS .. .de PE ..

groff itself does not provide direct conversion into other graphics file formats. But there are lots of possibilities if you first transform your picture into PostScript® format using the groff option -Tps. Since this ps-file lacks BoundingBox information it is not very useful by itself, but it may be fed into other conversion programs, usually named ps2other or pstoother or the like. Moreover, the PostScript interpreter Ghostscript (gs(1)) has buil-in graphics conversion devices that are called with the option

: gs -sDEVICE=<devname>

Call

: gs --help

for a list of the available devices.

An alternative may be to use the -Tpdf option to convert your picture directly into PDF format. The MediaBox of the file produced can be controlled by passing a -P-p papersize to groff.
As the Encapsulated PostScript File Format EPS is getting more and more important, and the conversion wasn't regarded trivial in the past you might be interested to know that there is a conversion tool named ps2eps which does the right job. It is much better than the tool ps2epsi packaged with gs.

For bitmapped graphic formats, you should use pstopnm; the resulting (intermediate) file can be then converted to virtually any graphics format using the tools of the netpbm package.