This section describes only the differences between GNU pic and
the original version of pic. Many of these differences also
apply to newer versions of Unix pic. A complete documentation is
available in the file
/usr/local/share/doc/groff-1.23.0/pic.ms
TeX mode
TeX mode is enabled by the -t option. In TeX mode, pic will
define a vbox called \graph for each picture. Use the figname
command to change the name of the vbox. You must yourself print
that vbox using, for example, the command
\centerline{\box\graph}
Actually, 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 make the vbox having a positive height and a depth of zero (as
used e.g., by LaTeX's graphics.sty), define the following macro
in your document:
\def\gpicbox#1{%
\vbox{\unvbox\csname #1\endcsname\kern 0pt}}
Now you can simply say \gpicbox{graph} instead of \box\graph.
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 to change the value of
\baselineskip. Anything else may well produce undesirable
results; use at your own risk. Lines beginning with a period are
not given any special treatment.
Commands
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 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
occurring in if-true. Y can be any character not
occurring in if-false.
print arg...
Concatenate the arguments and print as a line on the
standard error stream. Each arg must be an expression, a
position, or text. This is useful for debugging.
command arg...
Concatenate the arguments and pass them through as a line
to troff or TeX. Each arg must be an expression, a
position, or text. This has a similar effect to a line
beginning with . or \, but allows the values of variables
to be passed through. For example,
.PS
x = 14
command ".ds string x is " x "."
.PE
\*[string]
prints
x is 14.
sh X command X
Pass command to a shell. X can be any character not
occurring in command.
copy "filename"
Include filename at this point in the file.
copy ["filename"] thru X body X [until "word"]
copy ["filename"] thru macro [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
is equivalent to
.PS
circle at (1,2)
circle at (3,4)
circle at (5,6)
box
.PE
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.
reset
reset variable1[,] variable2 ...
Reset pre-defined variables variable1, variable2 ... to
their default values. If no arguments are given, reset
all pre-defined variables to their default values.
Assigning a value to scale also causes all pre-defined
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 "%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.
variable := expr
This is similar to = except variable must already be
defined, and expr will be assigned to variable without
creating a variable local to the current block. (By
contrast, = defines the variable in the current block if
it is not already defined there, and then changes the
value in the current block only.) For example, the
following:
.PS
x = 3
y = 3
[
x := 5
y = 5
]
print x y
.PE
prints
5 3
Arguments of the form
X anything X
are also allowed to be of the form
{ anything }
In this case anything can contain balanced occurrences of { and
}. Strings may contain X or imbalanced occurrences of { and }.
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
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" 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 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 flags '#', '-', '+', and ' ' [sp]ace), a minimum field width,
an optional precision, and the conversion specifications %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,
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.
Three additional modifiers are available to specify colored
objects: outline[d] sets the color of the outline, shaded the
fill color, and colo[u]r[ed] sets both. All three keywords
expect a suffix specifying the color, as shown below.
circle shaded "green" outline "black"
Currently, color support isn't available in TeX mode. Predefined
color names for groff are in the device macro files, for example
ps.tmac; additional colors can be defined with the .defcolor
request (see the manual page of troff(1) for more details).
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:
.PS
figname = 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, 'exprth' 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
}
