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.
TeXmode
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 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 \baselineskip.
Anything else may well 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 will define 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}
for instance. Since the vbox has a height of zero (it is defined with \vtop) this will produce slightly
more vertical space above the picture than below it;
\centerline{\raise 1em\box\graph}
would avoid this. To give the vbox a positive height and a depth of zero (as used by LaTeX's
graphics.sty, for example) define the following macro in your document.
\def\gpicbox#1{%
\vbox{\unvbox\csname #1\endcsname\kern 0pt}}
You can then simply say \gpicbox{graph} instead of \box\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.
forvariable=expr1toexpr2 [by [*]expr3] doXbodyX
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.
ifexprthenXif-trueX [elseYif-falseY]
Evaluate expr; if it is non-zero then do if-true, otherwise do if-false. X can be any character
not occurring in if-true. Y can be any character not occurring in if-false.
printarg ...
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.
commandarg ...
Concatenate arguments and pass them as a line to troff or TeX. 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
\*[string]
produces
x is 14.
when formatted with troff.
shXcommandX
Pass command to a shell.
copy"filename"
Include filename at this point in the file.
copy ["filename"] thruXbodyX [until "word"]
copy ["filename"] thrumacro [until "word"]
This construct does body once for each line of filename; the line is split into blank-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,
.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.
resetresetpvar1[,] 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.
plotexpr ["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 "%g" 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,
.PSx=3y=3[x:=5y=5]printxy.PE
writes
5 3
to the standard error stream.
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)!ee1&&e2e1||e2e1==e2e1!=e2e1>=e2e1>e2e1<=e2e1<e2"str1"=="str2""str1"!="str2"
String comparison expressions must be parenthesised in some contexts to avoid ambiguity.
Otherchanges
A bare expression, expr, is acceptable as an attribute; it is equivalent to direxpr, where dir is the
current direction. For example
line2i
means draw 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.
Scientific notation is allowed for numbers. For example
x=5e-2
Text attributes can be compounded. For example,
"foo"aboveljust
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 TeX mode splines can be dotted or dashed also.
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. 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("format",arg, ...)
can also be used; this will produce the arguments formatted according to format, which should be a string
as described in printf(3) appropriate for the number of arguments supplied. Only the modifiers “#”, “-”,
“+”, and “ ” [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 TeX output mode, this
means use a thickness of 8 milliinches; in TeX 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,
circlethickness1.5
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 "green" outline "black"
Color is not yet supported in TeX mode. Device macro files like ps.tmac declare color names; you can
define additional ones with the defcolor request (see groff(7)).
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. Example:
.PSfigname=foobar;....PE
The picture is then available in the box \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 non-zero and either TeX 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 device-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 grops(1) or
gropdf(1). 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, 'expr'th is also allowed. “'th“ is a single token: no space is allowed
between the apostrophe and the “th”. For example,
for i = 1 to 4 do {
line from 'i'th box.nw to 'i+1'th box.se
}
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