DPIC(1)

NAME
dpic - convert pic-language input to LaTeX-compatible and other formats

SYNOPSIS
dpic [ -efghmprstvxz ] [infile] [> outfile]

Typically infile is of the form name[.pic] and outfile is of
the form name[.tex|.eps|.fig|.mp|.svg]

OPTIONS

(none)
    LaTeX drawing output (very limited font-based drawing capability)

-e  pict2e output

-f  Postscript output, strings in psfrag format

-g  TikZ-pgf output

-h  write help message and quit

-m  mfpic output (see mfpic documentation)

-p  PSTricks output

-r  raw Postscript output, no automatic string formatting

-s  MetaPost output

-t  eepicemu output (slightly less limited than LaTeX drawing output)

-v  svg output

-x  xfig 3.2 output

-z  safe mode (access to external files disabled)

DESCRIPTION
dpic accepts a tight subset of the pic drawing language accepted by GNU pic (sometimes named gpic) or AT&T pic, and emits lower-level drawing commands for insertion into LaTeX documents, for processing by the xfig or Inkscape drawing tools, or for direct display as encapsulated Postscript or SVG. Arbitrary text can be inserted into the output for later formatting, and arbitrary commands for the postprocessor (PSTricks, Tikz-pgf, etc.) can be included. Language extensions unique to dpic are also implemented for specific purposes.

LANGUAGE SUMMARY
Input consists of a sequence of lines. The first line of a picture is .PS and the last is .PE, with lines between these two converted into low-level drawing commands for the postprocessor chosen by the option. Lines outside of .PS ... .PE pass through dpic unchanged.

  Coordinates
Coordinate axes in the pic language point to the right and up. The drawing units are inches by default but the statement

   scale = 25.4

at the beginning of the diagram has the effect of changing the units to millimetres.

  Drawn objects
The primitive drawn objects consist of the planar objects box, circle, ellipse; the linear objects line, arrow, move, spline; and arc, which has characteristics of both planar and linear objects. A block is a pair of square brackets enclosing other objects: [ anything ] and is a planar object. The complete diagram is contained implicitly in a block.

A string is a planar object similar to a box, but the pic language also allows strings to be attached to other objects as overlays, in which case they are part of the object.

The current drawing position Here is always defined. Initially and at the beginning of a block, Here is 0,0. Similarly, the current direction, which can be any of up, down, left, right, is set as right initially.

Each drawn object has an entry point and exit point, which depend on the current direction. The entry point is placed by default at the current position. Objects can also be placed explicitly with respect to absolute coordinates or relative to other objects. The exit point becomes the new current position.

  Labels
A label in pic is an alphameric sequence that starts with an uppercase letter. dpic allows variables and labels to be subscripted; thus T and T[5] are distinct labels. The value in brackets can be any expression but it is rounded to the nearest integer value. A label gives a symbolic name to a position or drawn object; for example,

   Post: position.

  Defined points
Once drawn, a linear object has defined points .start, .center, and .end, which can be referenced as known positions, for example,

L: line; line up 0.5 from L.c

where .center has been abbreviated as .c

The defined points for a planar object are the compass points on its periphery given by .n, .s, .e, .w, .nw, .ne, .se, .sw, together with .center, .top, .bottom, .right, .left. For an arc, these points correspond to the circle of which the arc is a part, with the addition of .start and .end.

A block has defined points similar to a box, but can also have others in its interior. Using the example

A: [ circle; Q: [ line; circle ]; T: Q.n ]

the defined points are as follows:

   The points of the outer block as if it were a box, for
   example, A.ne

   A position defined in the block, for example, A.T

   The defined points of labeled objects inside the block,
   preceded by a dot, for example, A.Q (the centre of
   block Q), or A.Q.ne (the northeast corner of Q).

   The defined points of enumerated objects inside the
   block, preceded by a dot (but make sure there is a space
   after the dot if it is followed by a number rather than
   an expression in braces), for example, A.Q. 1st circle.n
   or (better) A.Q.{1}st circle.n

  Language elements
The lines defining a picture are separated by newline characters or semicolons. Newlines are significant except after then, ;, :, {, else, or newline.

A line is continued to the next if the rightmost character is a backslash.

Lines beginning with a period are ignored, except for .PS and .PE lines.

The pic source may be commented by placing each comment to the right of a # character (unless the # is in a string).

The language elements include the following:

   A drawing command with optional label, for example,
box or A: box

   A position-label definition, for example A: position

   An assignment to a variable, for example x = 5

   A direction (to change the default), for example, up

Branching is performed by

if expr then { dotrue } else { dofalse }.

The looping facility is

for variable = expr to expr [by incr[*]] do { anything }.

The number of iterations must be computable in advance, and the repeated statements cannot change the value of variable. The loop variable is incremented by 1 by default, otherwise by incr (which may be negative) unless it is followed by the asterisk, in which case the loop variable is multiplied by incr.

Braces occur in several contexts. When used independently of other language elements, as

   { anything }

the left brace saves the current position and direction, and the right brace restores them to the saved values after the enclosed lines have been obeyed.

Arbitrary postprocessor commands can be generated using

command string,

which inserts the contents of string into the output. The string contents must be compatible with the chosen postprocessor. Similarly, any line that begins with a backslash is copied literally to the output.

The line

exec string

executes the contents of string as if it were a normal input line.

To execute shell commands, use

sh string

and to read lines from an external file, use

copy string

These commands are disabled by the dpic option -z or by a compile-time switch.

The command

print expr|position|string [ > string | >> string ]

prints or appends its argument to the file named in the string on the right, or by default to the standard error. Printing to a file is turned off by the -z option.

  Macros
The pic language includes macro definition and expansion, using

define name { anything },

so that, when name appears alone or with arguments as name(arg,...) then it is replaced by the contents between the braces in the definition. A comma in an argument is ignored if it is in a string or parentheses. In this substitution, occurrences of $1 are replaced by the first argument, and so on for other arguments. The value $+ in a macro is the number of arguments given to the macro. dpic ignores white space (spaces, new lines, and tab characters) that directly precede an argument in a macro invocation. A macro definition can be deleted by

undefine name

Macro definitions are global, which may require judicious undefinition of macros if there is a risk of name clashes.

  Drawing commands
An object is drawn using the following general format:

[Label:] object [attributes] [placement] [strings]

The items following object can occur in any order, but the order can make a difference to the drawn result, since lines are read and interpreted from left to right. Defaults are assumed for all drawing parameters as necessary. For example, the sequence

circle "Chew"; arrow; box "Swallow"
line; arc cw; ellipse "Digest"

draws a simple flow diagram using default sizes for all objects, with centered words in the circle, box, and ellipse.

  Attributes
The size and other parameters control the appearance of objects. An attribute is a keyword or keywords with expressions as appropriate.

The dimension attributes are the following, showing valid abbreviations:

height|ht|width|wid|radius|rad|diameter|diam|scaled expr

When appended to linear objects, height and width apply to arrowhead dimensions. The scaled attribute scales the object by expr.

The postprocessed size of a string is unknown in advance to the pic processor, but once known, the bounding box dimensions can be specified explicitly as for other drawn objects.

The thickness of lines defining an object are modified using the environmental variable linethick or the attribute

thickness|thick expr

expressed in points. Line thickness is independent of any scaling.

Solid lines are drawn by default; this can be modified with

solid|dotted|dashed|invisible|invis

The following attributes are for putting arrowheads at the start, end, or both ends of a linear object:

<-|->|<-> expr

The shape parameter expr may be omitted, in which case the value of the environment variable arrowhead is used. The default for arrow is ->.

The drawing direction of an arc is changed by the attribute

ccw|cw

with ccw the default.

To fill an object or path with a shade of gray, use the attribute

fill expr

where a value of 1 means white, and 0 means black. Paths can be filled where the postprocessor allows.

Line color can be set using

outline|outlined string

where the contents of the string depend on the postprocessor. The predefined colours of LaTeX or Tikz-pdf packages can be specified. The pic language knows no details about color; the string contents must be compatible with the postprocessor. Custom colors have to be defined using the

command string

facility so that the postprocessor will know about them.

Filling by color is similar, using the attribute

shaded string

and, when both the fill and outline colors are the same, the two attributes can be combined as

colour|color|colored|coloured string

in which all four spellings are equivalent.

Finally, the attribute

same

duplicates the properties of the previously drawn object of the same type, but with the current default placement.

In addition to scale changes effected by the scale variable, the size of the complete picture can be set by appending one or two terms to the .PS line as shown:

.PS [x [y]]

where x and y evaluate to constant values. On encountering the .PE line, the picture width w and height h are calculated. If x > 0 then the picture is scaled so that w = x. If h > y > 0 or if x = 0 and y > 0 then the picture is scaled so that h = y. Horizontal and vertical scaling are not independent. Text size, line thickness, and arrowheads are not scaled. The dimensions are inches, so for example,

.PS 100/25.4

sets the final picture width to 100 mm. Printed string text may extend beyond the rectangular boundaries defined by w and h unless the text dimensions have been explicitly set.

If the final diagram width exceeds maxpswid or the height exceeds maxpsht then the diagram is scaled as for x and y above.

  Placement of drawn objects
An object is placed by default so that its entry is at the current point.

Explicit placement is obtained with

object at position

which centers the object at position, or

object with defined point at position

for example,

arc cw from position to position with .c at position

A block can also be positioned by reference to a displacement from its lower left corner, for example,

A: [ contents ] with (0.5,0.2) at position.

Linear objects are placed by default with the .start point placed at the current drawing postion; otherwise linear objects are defined using a linespec, which is of the form

linespec = from position | to position | direction [expr]
| linespec linespec
| linespec then linespec

where the second line means that linespecs can be concatenated, and the third that multisegment linear objects are drawn using multiple linespecs separated by then.

As an example, the following draws a triangle with the leftmost vertex at the current point:

line up 2 right 1.5 then down 3 then to Here

Exceptionally, the linespec

to position to position to ...

is multiple and does not require the then keyword.

A single expr is also an acceptable linespec immediately after a linear object and means that the object is drawn to length expr in the current direction. The exception to this is

spline [expr] linespec

for which the expr is a spline tension parameter. If expr is omitted, a straight line is drawn to the midpoint of the first two spline control points and from the midpoint of the last two to the last point; the spline is tangent to all midpoints between control points. If expr is present, the spline is tangent at the first and last control points and at all other midpoints, and the spline tension can be adjusted. Tension values between 0 and 1 are typical.

In cases where all of the points of a multisegment linear object are not known in advance or inconvenient to calculate, the drawing command

continue linespec

will append a segment to the previously drawn linear object as if continue were then, with two differences. Arbitrary calculations may be done between the previous object and the continue statement, and the current point is the exit point of the previous object.

The construction

line from position to position chop expr

truncates the line at each end by the value of expr or, if expr is omitted, by the current circle radius. Otherwise

line from position to position chop expr1 chop expr2

truncates the line by the two specified distances at the ends. Truncation values can be negative.

The attribute

by position

is for positioning, for example,

move by (5,6)

  Variables and expressions
Variable names are alphameric sequences beginning with a lower-case letter, optionally subscripted as for labels, and are defined by assignment. For example, the following line defines the variable x if it does not already exist in the current scope:

x = expr

The scope of pic variables is the current block in which they are defined, including blocks defined later within the current block. The assignment

x := expr

requires x to have been defined previously.

Expressions consist of floating-point values combined using the unary operator "!" for logical negation and the usual parentheses and binary operators in decreasing order of precedence:

   ^
   * / %
   + -
   == != >= <= < >
   &&
   ||

A floating-point value is obtained as an integer, a number with e syntax, a function value, a size value of a drawn object, for example,

last box.ht,

or the horizontal or vertical coordinate of a position, obtained respectively as

position .x|.y

The one-argument functions are abs, acos, asin, cos, exp, expe, int, log, loge, sign, sin, sqrt, tan, floor. The functions exp and log are base 10. The function rand() delivers a random number between 0 and 1, and rand (expr) initializes the random number generator.

The two-argument functions are atan2, max, min, pmod where pmod is the modulo function delivering a positive value.

  Predefined environment variables
A set of predefined variables establishes the default values of drawing parameters. Their values are inherited from the superior block, but can be changed by assignment. They can be used in expressions like other variables. The variables, their default values, and default uses are given below

arcrad 0.25 arc radius
arrowht 0.1 length of arrowhead
arrowwid 0.05 width of arrowhead
boxht 0.5 box height
boxrad 0 radius of rounded box corners
boxwid 0.75 box width
circlerad 0.25 circle radius
dashwid 0.05 dash length for dashed lines
ellipseht 0.5 ellipse height
ellipsewid 0.75 ellipse width
lineht 0.5 height of vertical lines
linewid 0.5 length of horizontal lines
movewid 0.5 length of horizontal moves
movewid 0.5 length of horizontal moves
textht 0 assumed height of text
textoffset 2.5/72 text justification gap
textwid 0 assumed width of text

When a value is assigned to the variable scale, all of the above values are multiplied by the new value of scale. The drawing units are thereby changed but the default physical sizes of drawn objects remain unchanged since, on final output, dimensions are divided by the scale value. In addition, the following are unchanged by scale:

arrowhead 1 arrowhead shape
fillval 0.5 fill density
linethick 0.8 line thickness in points
maxpsht 11.5 maximum allowed diagram height
maxpswid 8.5 maximum allowed diagram width
scale 1 drawing unit scale factor

The variables maxpswid and maxpsht may have to be redefined for large diagrams or landscape figures, for example.

  Positions
A position is equivalent to a coordinate pair defined in current drawing units, and can be expressed in the following forms:

Here
   The current drawing position.

expr,expr
   A pair of expressions separated by a comma.

(position)
   A position in parentheses for grouping.

(position,position)
   Takes the horizontal value from the first position and
   the vertical value from the second.

position +|- position
   Vector addition.

position *|/ expr
   Scalar postmultiplication.

Label
   The label of a defined position or object. The position
   is the center of the object.

expr [of the way] between position and position
   The example x between A and B is equal to A*(1-x) + B*x.
   Any value of expr is allowed.

expr < position, position >
   An abbreviated equivalent of the previous form.

number st|rd|nd|th [last] object
   An enumerated object within the current block.
   The object is one of line, move, arrow, arc, box,
ellipse, circle, spline, [],"" . The number can be
   replaced by { expr }. For example, last "" means the
   last string, and {2^2}nd [] means the fourth block in the
   current scope. The position is the center of the object.

Parentheses may be required when composite positions or expressions are used in the above forms.

Finally, a position can be expressed as

object . defined point

  Strings
A string is a sequence of characters enclosed in double quotes. To include a double quote in a string, precede it with a backslash. Strings can be concatenated using the + operator. The C-like function

sprintf (format string,expr,...)

is equivalent to a string. Expressions are floating-point values, so the only applicable number formats are e, f, and g.

Multiple strings such as "text1" "text2" are stacked and centered vertically.

A string attached to an object overlays the object at the center, and any height or width attributes apply to the object, not the string. However, the justification attributes ljust and rjust can be applied to the individual strings of a stack overlaying an object.

An independent string is placed with its center at a defined point, which is either the current point or defined by placement as for any object, for example,

"Crunchy crackers" wid 82.3/72 ht 9.7/72 with .sw at Q

The placement qualifiers above, below, ljust, rjust place the string above, below, or justified with respect to the placement point. For example,

"Crunchy crackers" at Q ljust above

places the string above and textoffset units to the right of Q.

EXAMPLES
Source file example.pic:

  \documentclass{article}
  \begin{document}
  .PS
  box dashed "Hello" "World"
  .PE
  \end{document}

The command

dpic -g example.pic > example.tex; pdflatex example produces example.pdf containing a dashed box with Hello and World stacked inside.

Similarly, the picture source

  .PS
  \definecolor{puce}{rgb}{0.8,0.53,0.6}%
  box shaded "puce"
  .PE

produces a box filled with a flea-like color when processed with dpic -g and pdflatex.

To produce a .tex file containing PSTricks drawing commands for insertion into a LaTeX document using the \input command, delete the first, second, and last lines in the first source above and process using the -p option of dpic.

SEE ALSO

E. S. Raymond, E. S., "Making Pictures With GNU PIC," 1995.
In GNU groff source distribution;
http://www.kohala.com/start/troff/gpic.raymond.ps
(A good introduction to the pic language, with elementary illustrations.)

J. D. Aplevich, "Drawing with dpic," 2010,
http://ece.uwaterloo.ca/~aplevich/dpic/dpicdoc.pdf
(Specific discussion of dpic facilities and extensions, with differences between dpic and GNU pic.)

B. W. Kernighan, B. W. and D. M. Richie, "PIC - A Graphics Language for Typesetting, User Manual,", 1991.
AT&T Bell Laboratories, Computing Science Technical Report
116. (The original Unix pic.)

J. D. Aplevich, "M4 Macros for Electric Circuit Diagrams in LaTeX Documents," 2010. File CMman.pdf in the graphics/Circuit_macros section of CTAN repositories. (Extension of the pic language using the m4 macro processor for drawing electric circuits and other diagrams.)

AUTHOR
    Dwight Aplevich <aplevich at uwaterloo dot ca>