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researchv10 Dan Cross

.TH prtx 5G "WH" MARX
.SH NAME
prtx \- format of prtx commands
.SH DESCRIPTION
.P
Commands are in ascii characters and
are terminated by either a ";" or a newline character.
Besides commands there are "prefixes" that modify the 
following a command.
.P
Most commands and prefixes take arguments.  
These are often numbers or
point positions. 
The latter being a pair of numbers.
Numbers can be arbitrary
arithmetic expressions involving "+", "-", "*" or "/", numeric
constants, and parenthesis.  
A numeric constant is a decimal number (optionally  
including a decimal point and fraction) followed by a scale.  
A scale is "i", for inches,
"c" for characters, or "d" for dots.  (A dot is the smallest resolution
on the printer.) If the scale is omitted "c" is assumed.  Constants
used in multiplication or division should omit the scale.
.PP
Point positions are specified by a row position and a column position, 
separated by white space (blanks or tabs).  
The upper left hand corner of the
page is 0 0.  Positions increase to the right and downward.
If a page contains 60 characters vertically and 80 horizontally.
the last horizontal dot is at 80c-1d and the last
vertical dot is at 60c-1d.
.PP
The commands are:
.TP 10
# comment
This command has no effect.  Note that it is terminated by a ";"
just like any other command.
.TP 10
line  point1 point2 ... 
Line Command: 
Straight lines are drawn starting at 
.I point1 
going to 
.I point2 
and then to further points.
At least two points must be given but there is no maximum.
Points may be separated by a "," for readability.
.TP 10
interp point1 point2 ...
Interpolate command:  
A curved line is drawn determined by the points. 
A point may be surrounded by curly braces ( '{' and '}' )
in which case it is a "guide" point.
The curve is a second degree spline that 
satisfies the following constraints:
.RS 10 
.IP
It passes through all normal points.
.IP
If two guide points are adjacent in the list it passes through
the point midway between them and is tangent to the line connecting
them.
.IP 
If a normal point is adjacent in the list to a guide point the
curve as it passes through the normal point is tangent to
the line connecting it to the guide. 
.IP 
If a normal point is not adjacent on the list to a guide point
the curve, as it passes through the normal point, has the same tangent
as the circle that goes through that point and two neighboring points
on the list. This will be the preceding and the following
points for a point in the middle of the list. 
.P
Unfortunately these rules can result in cusps.  They seem to
work best in the cases where there are three normal points
(an approximation to a circular segment) or in 
the case where guide points are used to connect two normal
points.
.RE
.TP 10
ellipse center radius
Ellipse Command: An ellipse is drawn centered at
.I center,
with its shape determined by 
.I radius.
The ellipse's axes are parallel to the picture's.
.I radius
is two expressions.  The first determines the "vertical radius"
(i.e. half the length  of the ellipse's vertical axis) and the
second determines the "horizontal radius".  If they are equal
(as distances, not as number of dots or characters) the ellipse
is a circle.


.TP 10
text point text
Text Command:
Characters specified by 
.I text 
are placed on the output starting at 
.I point.
(The position is the upper left hand corner of the first character.)
.I  text 
begins at the first non blank character following the point
and continues to the end of the line. Embedded ";" are allowed,
and "C" type escapes are processed.  
An escaped newline (i.e. one immediately preceded by a backslash)
is treated as text and does not end the command.
A leading ":" is stripped off.
This is necessary if the first character desired is a space or 
arithmetic operator. 
.TP 10
stext point point text
Slanted text command: 
Text is placed in the output as with the simple text command except
the base line (the line running across the top of the characters)
is the line through the two points.
The text starts at the first point and may proceed any 
distance towards or beyond the second point.  
The second point provides a direction only, the characters are 
not stretched or compressed.
.TP 10
mtext point terminator
Multi line text command:
Lines following the one containing the command upto (but not including)
the first line that begins with the terminator character (default '.') 
are put in the output, with the first line positioned at \fIpoint\fR
and the following lines positioned vertically below the first.
.TP 10
smtext point [point] [ terminator ] [text ]
General form of the text command: 
The modifiers "s", "m", and "N" may be combined.  
If both "s" and "m" are present "s" must come first.
The second point is required present if "s" is present and "terminator"
is required if "m" is present. Otherwise they must be omitted.
If "m" is omitted then text must be present.
.TP 10
$X [ point ]
Macro Command: Invoke macro 
.I X. 
The the body of macro
.I X
is executed with an offset of
.I point. 
That is, positions in the body of the macro are taken as relative
to 
.I point. 
If 
.I point
is omitted it is take to be the origin.
The color and solidity in effect at the point invocation are
used in drawing unless they are explicitly overridden by a prefix
within the macro body.
An invoke command is legal within a macro body but care should be
taken to avoid a macro invoking itself.
.PP
Prefixes modify the following command, which is separated
from the prefix by white space only. 
However, commands can be grouped with braces 
(i.e the characters '{' and '}').
If the opening brace is in the same line as the prefix, 
commands my be on different lines, and the prefix applies to
all commands within the braces ;
Braces can be nested.
More than one prefix can modify a single command
The following prefixes are defined:
.TP 10
at point
Translation Prefixes:
Locations in the prefixed command are 
taken as relative to the argument of 
.I at.
.TP 10
expand factor
Expand Prefix:
The prefix command is expanded about the origin by 
.I factor, 
which is an unscaled numeric expression.  
That is, all positions and shapes are multiplied by 
.I factor.
.TP 10
rotate angle
Rotation Prefix:  
Locations in the prefixed command are rotated about the origin by 
.I angle
degrees.  
Text will still be horizontal, unless created with an \fIstext\fR 
command.
.TP 10
size N
Character Size Prefix: 
Characters in the prefixed command have their size multiplied
by N.  N must be and integer.
.TP 10
style solidity
Line Style Prefix:
The line drawing commands (line, ellipse, interp) will normally
draw solid lines but this can be changed by a \fIstyle\fR prefix.
Solidity is one of the following literals: solid, longdashed, dashed, 
dotdashed, dotted, invisible. 
Invisible lines are not drawn at all, so this style is useful in
taking up space in connection with the stack and shelf prefixes.
.TP 10
color colorname
Color prefix:
Every thing drawn by the following command will be in the named color.
Legal colors are: yellow, orange, red, green, blue, violet.
If the output device does not have colors this prefix is ignored.
.TP 10
boxit space 
Boxit Prefix:
Space consists of two numeric expressions, a row and a column spacing.
Boxit draws the prefixed command and an enclosing box.  The box is
drawn to leave the specified spaces at the top and bottom (row space),
and sides (column space) around the prefixed command.
.TP 10 ;
define X 
Define macro:
.I X
is any alphabetic character (lower and upper case are considered
identical) and the macro is defined as equivalent to the following
command.
The prefixed command, which must be a block 
(i.e. surrounded by braces),
becomes the body of the macro
and is not executed until the macro is invoked.
Once defined a macro character may not be redefined.
More elaborate macros can be obtained using a general 
macro processor such as 
.I m4
and the general arithmetic expressions provided by
.I prtx.
.TP 10 
stack
Stack commands:
The prefixed command must be a block.  Each command of the 
block is interpreted as if the origin had been moved to below
the earlier commands.  The effect is what would be achieved
if each command were prefixed by "at max 0", where max is the
maximum row contained in previous commands.  A row is contained
in a command if the command puts a dot in the row.  Text
commands also contain some blank space below the characters.
(In some circumstances, e.g. slanted text, 
\fIprtx\fR cannot easily compute the contained rows and
makes a guess.
But, arbitrary lines, and horizontal text work 
properly.)
.TP 10
shelf
Lay commands left to right.  This is like the
stack prefix except cammands are moved to the right rather than down.
.SH HISTORY
The current version of prtx also accepts an old form of the
command language.  It is compatibility with this old form
that makes the macro prefix require the prefixed command to
be a block.  In the future this restriction will disappear.
.SH FUTURE PLANS
.SH SEE ALSO
.I prtx(1)
.SH AUTHOR
Jerry Schwarz (harpo!jerry)

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