.TH groff_out @MAN5EXT@ "@MDATE@" "groff @VERSION@"
.SH Name
groff_out \- GNU
.I roff
intermediate output format
.
.
.\" XXX: This page needs review and editing.
.\" ====================================================================
.\" Legal Terms
.\" ====================================================================
.\"
.\" Copyright (C) 1989-2023 Free Software Foundation, Inc.
.\"
.\" This file is part of groff, the GNU roff type-setting system.
.\"
.\" Permission is granted to copy, distribute and/or modify this
.\" document under the terms of the GNU Free Documentation License,
.\" Version 1.3 or any later version published by the Free Software
.\" Foundation; with no Invariant Sections, with no Front-Cover Texts,
.\" and with no Back-Cover Texts.
.\"
.\" A copy of the Free Documentation License is included as a file
.\" called FDL in the main directory of the groff source package.
.
.
.\" Save and disable compatibility mode (for, e.g., Solaris 10/11).
.do nr *groff_groff_out_5_man_C \n[.cp]
.cp 0
.
.\" Define fallback for groff 1.23's MR macro if the system lacks it.
.nr do-fallback 0
.if !\n(.f           .nr do-fallback 1 \" mandoc
.if  \n(.g .if !d MR .nr do-fallback 1 \" older groff
.if !\n(.g           .nr do-fallback 1 \" non-groff *roff
.if \n[do-fallback]  \{\
.  de MR
.    ie \\n(.$=1 \
.      I \%\\$1
.    el \
.      IR \%\\$1 (\\$2)\\$3
.  .
.\}
.rr do-fallback
.
.
.\" ====================================================================
.\" Setup
.\" ====================================================================
.
.\" ================= Document configuration
.
.\" Number register to decide whether the commands '{' and '}' are used
.\" 0: disable (current default); 1: enable
.nr @USE_ENV_STACK 0
.
.ig
Unfortunately, old versions of groff used an illogical position change
after some D\~commands (Dp, DP, Dt).  If the register
@STUPID_DRAWING_POSITIONING is 1 (current default) then change position
after these commands, otherwise the position is not changed.
..
.nr @STUPID_DRAWING_POSITIONING 1
.
.\" ================= Semantical definitions
.
.nr @maxcolor 65536
.ds @backslash \[rs]\"
.ds @linebreak \fR\[la]line-break\[ra]\fP\"
.
.\" Begin of macro definitions
.
.de offset
.RI ( \,\\$1\/ ,\  \,\\$2\/ )\\$3
..
.de indexed_offset
.offset \fI\\$1\/\fP\d\s-3\\$2\s+3\u\x'\n[.v]/4' \fI\\$3\/\fP\
\d\s-3\\$4\s+3\u\x'\n[.v]/4' \\$5\x'\n[.v]/4'
..
.\" format: .command <name> "<arguments>" <punctuation>
.de command
\fB\\$1\fP\ \fI\,\\$2\/\fP\\$3
..
.\" format: .D-command <subcommand> "<arguments>"
.de D-command
\fBD\\$1\fP\ \fI\,\\$2\/\fP\|\*[@linebreak]
..
.
.\" We set these as troff micromotions rather than eqn because \d and \u
.\" can be lifted to XML subscript/superscript tags.  Don't change
.\" these to a parameterized string, man2html won't handle that.
.ds hv1 \fIh\d\s-3\&1\s+3\u\~v\d\s-3\&1\s+3\u\fP\x'\n[.v]/4'
.ds hv2 \fIh\d\s-3\&2\s+3\u\~v\d\s-3\&2\s+3\u\fP\x'\n[.v]/4'
.ds hvn \fIh\d\s-3\&n\s+3\u\~v\d\s-3\&n\s+3\u\fP\x'\n[.v]/4'
.
.de Da-command
\fBDa\fP\ \*[hv1] \*[hv2]\|\*[@linebreak]
..
.\" graphics command .D with a variable number of arguments
.\" format: .D-multiarg <subcommand>
.de D-multiarg
\fBD\\$1\fP\ \*[hv1] \*[hv2] \&.\|.\|.\& \*[hvn]\|\*[@linebreak]
..
.\" format: .x-command <subname> "<arguments>"
.de x-command
\fBx\\$1\fP\ \fI\\$2\fP\|\*[@linebreak]
..
.de xsub
.RI "(" "\\$1" " control command)"
.br
..
.\" End of macro definitions
.
.
.\" ====================================================================
.SH Description
.\" ====================================================================
.
The fundamental operation of the
.MR @g@troff @MAN1EXT@
formatter is the translation of the
.MR groff @MAN7EXT@
input language into a series of instructions concerned primarily with
placing glyphs or geometric objects at specific positions on a
rectangular page.
.
In the following discussion,
the term
.I command
refers to this intermediate output language,
never to the
.MR groff @MAN7EXT@
language intended for use by document authors.
.
Intermediate output commands comprise several categories:
glyph output;
font,
color,
and text size selection;
motion of the printing position;
page advancement;
drawing of geometric primitives;
and device control commands,
a catch-all for other operations.
.
The last includes directives to start and stop output,
identify the intended output device,
and embed URL hyperlinks in supported output formats.
.
.
.P
Because the front-end command
.MR groff @MAN1EXT@
is a wrapper that normally runs the
.I @g@troff
formatter to generate intermediate output
and an output driver (\[lq]postprocessor\[rq]) to consume it,
users normally do not encounter this language.
.
The
.I groff
program's
.B \-Z
option inhibits postprocessing such that this intermediate output is
sent to the standard output stream as when
.I @g@troff
is run manually.
.
.
.P
.IR groff 's
intermediate output facilitates the development of output drivers and
other postprocessors by offering a common programming interface.
.
It is an extension of the page description language developed by Brian
Kernighan for AT&T device-independent
.I troff \" AT&T
circa 1980.
.
Where a distinction is necessary,
we will say
.RI \[lq] @g@troff
output\[rq] to describe the output of GNU
.IR troff , \" GNU
and \[lq]intermediate output\[rq] to denote the language accepted by
the parser implemented in
.IR groff 's
internal C++ library used by most of its output drivers.
.\" XXX GBR leaves off here.
.
.
.\" ====================================================================
.SH "Language concepts"
.\" ====================================================================
.
During the run of
.IR @g@troff ,
the
.I roff
input is cracked down to the information on what has to be printed at
what position on the intended device.
.
So the language of the
.I intermediate output
format can be quite small.
.
Its only elements are commands with or without arguments.
.
In this document, the term \[lq]command\[rq] always refers to the
.I intermediate output
language, never to the
.I roff
language used for document formatting.
.
There are commands for positioning and text writing, for drawing, and
for device controlling.
.
.
.\" ====================================================================
.SS Separation
.\" ====================================================================
.
.I Classical troff output
had strange requirements on whitespace.
.
The
.I groff
output parser, however, is smart about whitespace by making it
maximally optional.
.
The whitespace characters, i.e., the
.IR tab ,
.IR space ,
and
.I newline
characters, always have a syntactical meaning.
.
They are never printable because spacing within the output is always
done by positioning commands.
.
.
.P
Any sequence of
.I space
or
.I tab
characters is treated as a single
.I syntactical
.IR space .
.
It separates commands and arguments, but is only required when there
would occur a clashing between the command code and the arguments
without the space.
.
Most often, this happens when variable length command names,
arguments, argument lists, or command clusters meet.
.
Commands and arguments with a known, fixed length need not be
separated by
.I syntactical
.IR space .
.
.
.P
A line break is a syntactical element, too.
.
Every command argument can be followed by whitespace, a comment, or a
newline character.
.
Thus a
.I syntactical line break
is defined to consist of optional
.I syntactical space
that is optionally followed by a comment, and a newline character.
.
.
.P
The normal commands, those for positioning and text, consist of a
single letter taking a fixed number of arguments.
.
For historical reasons, the parser allows stacking of such commands on
the same line, but fortunately, in
.I groff intermediate
.IR output ,
every command with at least one argument is followed by a line break,
thus providing excellent readability.
.
.P
The other commands \[em] those for drawing and device controlling \[em]
have a more complicated structure; some recognize long command names,
and some take a variable number of arguments.
.
So all
.B D
and
.B x
commands were designed to request a
.I syntactical line break
after their last argument.
.
Only one command,
.RB \[oq] x\ X \[cq]
has an argument that can stretch over several lines, all other
commands must have all of their arguments on the same line as the
command, i.e., the arguments may not be split by a line break.
.
.P
Lines containing only spaces and/or a comment are treated as empty and
ignored.
.
.
.\" ====================================================================
.SS "Argument units"
.\" ====================================================================
.
Some commands accept integer arguments that represent measurements,
but the scaling units of the formatter's language are never used.
.
Most commands assume a scaling unit
.RB of\~\[lq] u \[rq]
(basic units),
and others
.RB use\~\[lq] z \[rq]
(scaled points);
.
These are defined by the parameters specified in the device's
.I DESC
file;
see
.MR groff_font @MAN5EXT@
and,
for more on scaling units,
.MR groff @MAN7EXT@
and
.IR "Groff: The GNU Implementation of troff" ,
the
.I groff
Texinfo manual.
.
Color-related commands use dimensionless integers.
.
.
.P
Note that single characters can have the eighth bit set, as can the
names of fonts and special characters (this is, glyphs).
.
The names of glyphs and fonts can be of arbitrary length.
.
A glyph that is to be printed will always be in the current font.
.
.
.P
A string argument is always terminated by the next whitespace
character (space, tab, or newline); an embedded
.B #
character is regarded as part of the argument, not as the beginning of
a comment command.
.
An integer argument is already terminated by the next non-digit
character, which then is regarded as the first character of the next
argument or command.
.
.
.\" ====================================================================
.SS "Document parts"
.\" ====================================================================
.
A correct
.I intermediate output
document consists of two parts, the
.I prologue
and the
.IR body .
.
.P
The task of the
.I prologue
is to set the general device parameters using three exactly specified
commands.
.
The
.I groff prologue
is guaranteed to consist of the following three lines (in that order):
.RS
.P
.B x\ T
.I device
.br
.B x\ res
.I n\ h\ v
.br
.B x init
.RE
.P
with the arguments set as outlined in subsection \[lq]Device Control
Commands\[rq] below.
.
However, the parser for the
.I intermediate output
format is able to swallow additional whitespace and comments as well.
.
.
.P
The
.I body
is the main section for processing the document data.
.
Syntactically, it is a sequence of any commands different from the
ones used in the
.IR prologue .
.
Processing is terminated as soon as the first
.B x\ stop
command is encountered; the last line of any
.I groff intermediate output
always contains such a command.
.
.
.P
Semantically, the
.I body
is page oriented.
.
A new page is started by a
.BR p \~command.
.
Positioning, writing, and drawing commands are always done within the
current page, so they cannot occur before the first
.BR p \~command.
.
Absolute positioning (by the
.B H
and
.BR V \~commands)
is done relative to the current page, all other positioning
is done relative to the current location within this page.
.
.
.\" ====================================================================
.SH "Command reference"
.\" ====================================================================
.
This section describes all
.I intermediate output
commands, the classical commands as well as the
.I groff
extensions.
.
.
.\" ====================================================================
.SS "Comment command"
.\" ====================================================================
.
.TP
.BI # anything\c
\[la]line-break\[ra]
A comment.
.
Ignore any characters from the
.BR # \~character
up to the next newline.
.
Each comment can be preceded by arbitrary
.I syntactical
.IR space ;
every command can be terminated by a comment.
.
.
.\" ====================================================================
.SS "Simple commands"
.\" ====================================================================
.
The commands in this subsection have a command code consisting of a
single character, taking a fixed number of arguments.
.
Most of them are commands for positioning and text writing.
.
These commands are smart about whitespace.
.
Optionally,
.I syntactical space
can be inserted before, after, and between the command letter and its
arguments.
.
All of these commands are stackable, i.e., they can be preceded by
other simple commands or followed by arbitrary other commands on the
same line.
.
A separating
.I syntactical space
is necessary only when two integer arguments would clash or if the
preceding argument ends with a string argument.
.
.
.if \n[@USE_ENV_STACK]=1 \{\
.TP
.command {
Open a new environment by copying the current device configuration data
to the environment stack.
.
The current environment is setup by the device specification and
manipulated by the setting commands.
.
.
.TP
.command }
Close the current environment
(opened by a preceding
.BR { \~command)
and restore the previous environment from the environment
stack as the current device configuration data.
.
.\}              \" endif @USE_ENV_STACK
.
.
.TP
.command C id \[la]white-space\[ra]
Typeset the glyph of the special character
.IR id .
.
Trailing syntactical space is necessary to allow special character names
of arbitrary length.
.
The drawing position is not advanced.
.\" XXX: Why does it matter that we read its size if we don't advance
.\" the drawing position?
.\" its size is read from the font description file.
.
.
.TP
.command c c
Typeset the glyph of the ordinary character
.RI character\~ c .
.
The drawing position is not advanced.
.\" XXX: Why does it matter that we read its size if we don't advance
.\" the drawing position?
.\" its size is read from the font description file.
.
.
.TP
.command f n
Select the font mounted at
.RI position\~ n .
.
.IR n\~ cannot
be negative.
.
.
.TP
.command H n
Horizontally move the drawing position to
.IR n\~ basic
units from the left edge of the page.
.
.IR n\~ cannot
be negative.
.
.
.TP
.command h n
Move the drawing position right
.I n
basic units.
.
AT&T
.I troff \" AT&T
allowed negative
.I n;
GNU
.I troff \" GNU
does not produce such values,
but
.IR groff 's
output driver library handles them.
.
.
.TP
.command m "scheme \f[R][\f[]component\f[R] .\|.\|.]"
Select the stroke color using the
.IR component s
in the color space
.IR scheme .
.
Each
.I component
is an integer between 0 and \n[@maxcolor].
.
The quantity of components and their meanings vary with each
.IR scheme .
.
This command is a
.I groff
extension.
.
.
.RS
.TP
.command mc "cyan magenta yellow"
Use the CMY color scheme with components
cyan,
magenta,
and yellow.
.
.
.TP
.command md
Use the default color
(no components;
black in most cases).
.
.
.TP
.command mg gray
Use a grayscale color scheme with a component ranging
between 0 (black) and \n[@maxcolor] (white).
.
.
.TP
.command mk "cyan magenta yellow black"
Use the CMYK color scheme with components
cyan,
magenta,
yellow,
and black.
.
.
.TP
.command mr "red green blue"
Use the RGB color scheme with components
red,
green,
and blue.
.RE
.
.
.TP
.command N n
Typeset the glyph with
.RI index\~ n
in the current font.
.
.IR n\~ is
normally a non-negative integer.
.
The drawing position is not advanced.
.
The
.B html
and
.B xhtml
devices use this command with
.RI negative\~ n
to produce unbreakable space;
the absolute value of
.I n
is taken and interpreted in basic units.
.
.
.TP
.command n b\~a
Indicate a break.
.
No action is performed;
the command is present to make the output more easily parsed.
.
The integers
.I b
.RI and\~ a
describe the vertical space amounts before and after the break,
respectively.
.
GNU
.I troff \" GNU
issues this command but
.IR groff 's
output driver library ignores it.
.
See
.B v
and
.BR V .
.
.
.TP
.command p n
Begin a new page,
setting its number
.RI to\~ n .
.
Each page is independent,
even from those using the same number.
.
The vertical drawing position is set to\~0.
.
All positioning,
writing,
and drawing commands are interpreted in the context of a page,
so a
.BR p \~command
must precede them.
.
.
.TP
.command s n
Set type size to
.I n
scaled points
.RB (unit\~ z
in GNU
.IR troff ). \" GNU
.
AT&T
.I troff \" AT&T
used unscaled points
.RB ( p )
instead;
see section \[lq]Compatibility\[rq] below.
.
.
.TP
.command t xyz\f[R]\|.\|.\|.\& \f[R]\[la]white-space\[ra]
.TQ
.command t "xyz\f[R]\|.\|.\|.\&\f[] dummy-arg" \[la]white-space\[ra]
Typeset word
.IR xyz ;
that is,
set a sequence of ordinary glyphs named
.IR x ,
.IR y ,
.IR z ,
\&.\|.\|.\|,
terminated by a space or newline;
an optional second integer argument is ignored
(this allows the formatter to generate an even number of arguments).
.\" XXX: Why?
.
Each glyph is set at the current drawing position,
and the position is then advanced horizontally by the glyph's width.
.
A glyph's width is read from its metrics in the font description file,
scaled to the current type size,
and rounded to a multiple of the horizontal motion quantum.
.
Use the
.B C
command to emplace glyphs of special characters.
.
The
.BR t \~command
is a
.I groff
extension and is output only for devices whose
.I DESC
file contains the
.B tcommand
directive;
see
.MR groff_font @MAN5EXT@ .
.
.
.TP
.command u "n xyz"\f[R]\|.\|.\|.\& \f[R]\[la]white-space\[ra]
.TQ
.command u "xyz\f[R]\|.\|.\|.\&\f[] dummy-arg" \[la]white-space\[ra]
Typeset word
.I xyz
with track kerning.
.
As
.BR t ,
but after placing each glyph,
the drawing position is further advanced horizontally
.RI by\~ n
basic units.
.
The
.BR u \~command
is a
.I groff
extension and is output only for devices whose
.I DESC
file contains the
.B tcommand
directive;
see
.MR groff_font @MAN5EXT@ .
.
.
.TP
.command V n
Vertically move the drawing position to
.IR n\~ basic
units from the top edge of the page.
.
.IR n\~ cannot
be negative.
.
.
.TP
.command v n
Move the drawing position down
.I n
basic units.
.
AT&T
.I troff \" AT&T
allowed negative
.I n;
GNU
.I troff \" GNU
does not produce such values,
but
.IR groff 's
output driver library handles them.
.
.
.TP
.command w
Indicate an inter-word space.
.
No action is performed;
the command is present to make the output more easily parsed.
.
Only adjustable,
breakable inter-word spaces are thus described;
those resulting from
.B \[rs]\[ti]
or horizontal motion escape sequences are not.
.
GNU
.I troff \" GNU
issues this command but
.IR groff 's
output driver library ignores it.
.
See
.B h
and
.BR H .
.
.
.\" ====================================================================
.SS "Graphics commands"
.\" ====================================================================
.
Each graphics or drawing command in the
.I intermediate output
starts with the letter\~\c
.B D
followed by one or two characters that specify a subcommand; this
is followed by a fixed or variable number of integer arguments that
are separated by a single space character.
.
A
.BR D \~command
may not be followed by another command on the same line (apart from a
comment), so each
.BR D \~command
is terminated by a
.I syntactical line
.IR break .
.
.
.P
.I @g@troff
output follows the classical spacing rules (no space between command
and subcommand, all arguments are preceded by a single space
character), but the parser allows optional space between the command
letters and makes the space before the first argument optional.
.
As usual, each space can be any sequence of tab and space characters.
.
.
.P
Some graphics commands can take a variable number of arguments.
.
In this case, they are integers representing a size measured in basic
units\~\c
.BR u .
.
The
.I h
arguments
stand for horizontal distances where positive means right, negative
left.
.
The
.I v
arguments
stand for vertical distances where positive means down, negative up.
.
All these distances are offsets relative to the current location.
.
.
.P
Unless indicated otherwise, each graphics command directly corresponds
to a similar
.I groff
.B \*[@backslash]D
escape sequence; see
.MR groff @MAN7EXT@ .
.
.
.P
Unknown
.BR D \~commands
are assumed to be device-specific.
.
Its arguments are parsed as strings; the whole information is then
sent to the postprocessor.
.
.
.P
In the following command reference, the syntax element
.I \[la]line-break\[ra]
means a
.I syntactical line break
as defined in subsection \[lq]Separation\[rq] above.
.
.
.TP
.D-multiarg \[ti]
Draw B-spline from current position to offset
.indexed_offset h 1 v 1 ,
then to offset
.indexed_offset h 2 v 2
if given, etc., up to
.indexed_offset h n v n .
This command takes a variable number of argument pairs; the current
position is moved to the terminal point of the drawn curve.
.
.
.TP
.Da-command
Draw arc from current position to
.indexed_offset h 1 v 1 \|+\|\c
.indexed_offset h 2 v 2
with center at
.indexed_offset h 1 v 1 ;
then move the current position to the final point of the arc.
.
.
.TP
.D-command C d
.TQ
.D-command C "d dummy-arg"
Draw a solid circle using the current fill color with diameter\~\c
.I d
(integer in basic units\~\c
.BR u )
with leftmost point at the current position; then move the current
position to the rightmost point of the circle.
.
An optional second integer argument is ignored (this allows the
formatter to generate an even number of arguments).
.
This command is a
.I groff
extension.
.
.
.TP
.D-command c d
Draw circle line with diameter\~\c
.I d
(integer in basic units\~\c
.BR u )
with leftmost point at the current position; then move the current
position to the rightmost point of the circle.
.
.
.TP
.D-command E "h v"
Draw a solid ellipse in the current fill color with a horizontal
diameter of\~\c
.I h
and a vertical diameter of\~\c
.I v
(both integers in basic units\~\c
.BR u )
with the leftmost point at the current position; then move to the
rightmost point of the ellipse.
.
This command is a
.I groff
extension.
.
.
.TP
.D-command e "h v"
Draw an outlined ellipse with a horizontal diameter of\~\c
.I h
and a vertical diameter of\~\c
.I v
(both integers in basic units\~\c
.BR u )
with the leftmost point at current position; then move to the
rightmost point of the ellipse.
.
.
.TP
.D-command F "color-scheme \fR[\fPcomponent\fR .\|.\|.]\fP"
Set fill color for solid drawing objects using different color
schemes; the analogous command for setting the color of text, line
graphics, and the outline of graphic objects is
.BR m .
.
The color components are specified as integer arguments between 0 and
\n[@maxcolor].
.
The number of color components and their meaning vary for the
different color schemes.
.
These commands are generated by the
.I groff
escape sequences
.BR \*[@backslash]D\[aq]F\  .\|.\|. '
and
.B \*[@backslash]M
(with no other corresponding graphics commands).
.
This command is a
.I groff
extension.
.
.
.RS
.
.TP
.D-command Fc "cyan magenta yellow"
Set fill color for solid drawing objects using the CMY color scheme,
having the 3\~color components cyan, magenta, and yellow.
.
.
.TP
.D-command Fd
Set fill color for solid drawing objects to the default fill color value
(black in most cases).
.
No component arguments.
.
.
.TP
.D-command Fg "gray"
Set fill color for solid drawing objects to the shade of gray given by
the argument, an integer between 0 (black) and \n[@maxcolor] (white).
.
.
.TP
.D-command Fk "cyan magenta yellow black"
Set fill color for solid drawing objects using the CMYK color scheme,
having the 4\~color components cyan, magenta, yellow, and black.
.
.TP
.D-command Fr "red green blue"
Set fill color for solid drawing objects using the RGB color scheme,
having the 3\~color components red, green, and blue.
.
.RE
.
.
.TP
.D-command f n
The argument
.I n
must be an integer in the range \-32767 to 32767.
.
.RS
.TP
.RI 0\|\[<=]\| n \|\[<=]\|1000
Set the color for filling solid drawing objects to a shade of gray,
where 0 corresponds to solid white, 1000 (the default) to solid black,
and values in between to intermediate shades of gray; this is
obsoleted by command
.BR DFg .
.
.TP
.IR n "\|<\|0 or " n \|>\|1000
Set the filling color to the color that is currently being used for
the text and the outline, see command
.BR m .
For example, the command sequence
.
.RS
.IP
.EX
mg 0 0 \n[@maxcolor]
Df \-1
.EE
.RE
.
.IP
sets all colors to blue.
.
.P
This command is a
.I groff
extension.
.
.RE
.
.
.TP
.D-command l "h v"
Draw line from current position to offset
.offset h v
(integers in basic units\~\c
.BR u );
then set current position to the end of the drawn line.
.
.
.TP
.D-multiarg p
Draw a polygon line from current position to offset
.indexed_offset h 1 v 1 ,
from there to offset
.indexed_offset h 2 v 2 ,
etc., up to offset
.indexed_offset h n v n ,
and from there back to the starting position.
.
.ie \n[@STUPID_DRAWING_POSITIONING]=1 \{\
For historical reasons, the position is changed by adding the sum of
all arguments with odd index to the current horizontal position and the
even ones to the vertical position.
.
Although this doesn't make sense it is kept for compatibility.
.
.\}
.el \{\
As the polygon is closed, the end of drawing is the starting point, so
the position doesn't change.
.\}
.
This command is a
.I groff
extension.
.
.
.TP
.D-multiarg P
The same macro as the corresponding
.B Dp
command with the same arguments, but draws a solid polygon in the
current fill color rather than an outlined polygon.
.
.if \n[@STUPID_DRAWING_POSITIONING]=1 \{\
The position is changed in the same way as with
.BR Dp .
.\}
.
This command is a
.I groff
extension.
.
.
.TP
.D-command t n
Set the current line thickness
.RI to\~ n
(an integer in basic
.RB units\~ u )
if
.IR n \|>\|0;
if
.IR n \|=\|0
select the smallest available line thickness;
otherwise,
the line thickness is made proportional to the type size,
which is the default.
.
.if \n[@STUPID_DRAWING_POSITIONING]=1 \{\
For historical reasons,
the horizontal position is changed by adding the argument to the current
horizontal position,
while the vertical position is not changed.
.
Although this doesn't make sense,
it is kept for compatibility.
.\}
.
This command is a
.I groff
extension.
.
.
.\" ====================================================================
.SS "Device control commands"
.\" ====================================================================
.
Each device control command starts with the letter
.B x
followed by a space character (optional or arbitrary space/\:tab in
.IR groff )
and a subcommand letter or word; each argument (if any) must be
preceded by a
.I syntactical
.IR space .
.
All
.B x
commands are terminated by a
.IR "syntactical line break" ;
no device control command can be followed by another command on the same
line (except a comment).
.
.P
The subcommand is basically a single letter, but to increase
readability, it can be written as a word, i.e., an arbitrary sequence
of characters terminated by the next tab, space, or newline character.
.
All characters of the subcommand word but the first are simply ignored.
.
For example,
.I @g@troff
outputs the initialization command
.B x\ i
as
.B x\ init
and the resolution command
.B x\ r
as
.BR "x\ res" .
.
But writings like
.B x\ i_like_groff
and
.B x\ roff_is_groff
are accepted as well to mean the same commands.
.
.P
In the following, the syntax element
.I \[la]line-break\[ra]
means a
.I syntactical line break
as defined in subsection \[lq]Separation\[rq] above.
.
.TP
.x-command F name
.xsub Filename
Use
.I name
as the intended name for the current file in error reports.
.
This is useful for remembering the original file name when
.I groff
uses an internal piping mechanism.
.
The input file is not changed by this command.
.
This command is a
.I groff
extension.
.
.
.TP
.x-command f "n\ s"
.xsub font
Mount font position\~\c
.I n
(a non-negative integer) with font named\~\c
.I s
(a text word);
see
.MR groff_font @MAN5EXT@ .
.
.
.TP
.x-command H n
.xsub Height
Set character height to\~\c
.I n
(a positive integer in scaled points\~\c
.BR z ).
.
.I Classical troff
used the unit points (\c
.BR p )
instead;
see section \[lq]Compatibility\[rq] below.
.
.
.TP
.x-command i
.xsub init
Initialize device.
.
This is the third command of the
.IR prologue .
.
.
.TP
.x-command p
.xsub pause
Parsed but ignored.
.
The classical documentation reads
.I pause device, can be
.IR restarted .
.
.
.TP
.x-command r "n\ h\ v"
.xsub resolution
Resolution is\~\c
.IR n ,
while
.I h
is the minimal horizontal motion, and
.I v
the minimal vertical motion possible with this device; all arguments
are positive integers in basic units\~\c
.B u
per inch.
.
This is the second command of the
.IR prologue .
.
.
.TP
.x-command S n
.xsub Slant
Set slant to\~\c
.I n
degrees (an integer in basic units\~\c
.BR u ).
.
.
.TP
.x-command s
.xsub stop
Terminates the processing of the current file; issued as the last
command of any
.I intermediate @g@troff
.IR output .
.
.
.TP
.x-command t
.xsub trailer
Generate trailer information, if any.
.
In
.BR groff ,
this is currently ignored.
.
.
.TP
.x-command T xxx
.xsub Typesetter
.
Set the name of the output driver to
.IR xxx ,
a sequence of non-whitespace characters terminated by whitespace.
.
The possible names correspond to those of
.IR groff 's
.B \-T
option.
.
This is the first command of the prologue.
.
.
.TP
.x-command u n
.xsub underline
Configure underlining of spaces.
.
If
.I n
is\~1, start underlining of spaces;
if
.I n
is\~0, stop underlining of spaces.
.
This is needed for the
.B cu
request in
.B @g@nroff
mode and is ignored otherwise.
.
This command is a
.I groff
extension.
.
.
.TP
.x-command X anything
.xsub X-escape
Send string
.I anything
uninterpreted to the device.
.
If the line following this command starts with a
.B +
character this line is interpreted as a continuation line in the
following sense.
.
The
.B +
is ignored, but a newline character is sent instead to the device, the
rest of the line is sent uninterpreted.
.
The same applies to all following lines until the first character of a
line is not a
.B +
character.
.
This command is generated by the
.I groff
escape sequence
.BR \*[@backslash]X .
.
The line-continuing feature is a
.I groff
extension.
.
.
.\" ====================================================================
.SS "Obsolete command"
.\" ====================================================================
.
In
.I classical troff
output, emitting a single glyph was mostly done by a very
strange command that combined a horizontal move and the printing of a
glyph.
.
It didn't have a command code, but is represented by a 3-character
argument consisting of exactly 2\~digits and a character.
.
.TP
.I ddc
Move right
.I dd
(exactly two decimal digits) basic units\~\c
.BR u ,
then print glyph with single-letter name\~\c
.IR c .
.
.
.RS
.P
In
.IR groff ,
arbitrary
.I syntactical space
around and within this command is allowed to be added.
.
Only when a preceding command on the same line ends with an argument
of variable length a separating space is obligatory.
.
In
.I classical
.IR troff ,
large clusters of these and other commands were used, mostly without
spaces; this made such output almost unreadable.
.
.RE
.
.
.P
For modern high-resolution devices, this command does not make sense
because the width of the glyphs can become much larger than two
decimal digits.
.
In
.IR groff ,
it is used only for output to the
.BR X75 ,
.BR X75\-12 ,
.BR X100 ,
and
.B X100\-12
devices.
.
For others,
the commands
.B t
.RB and\~ u
provide greater functionality and superior troubleshooting capacity.
.
.
.\" ====================================================================
.SH Postprocessing
.\" ====================================================================
.
The
.I roff
postprocessors are programs that have the task to translate the
.I intermediate output
into actions that are sent to a device.
.
A device can be some piece of hardware such as a printer, or a software
file format suitable for graphical or text processing.
.
The
.I groff
system provides powerful means that make the programming of such
postprocessors an easy task.
.P
There is a library function that parses the
.I intermediate output
and sends the information obtained to the device via methods of a
class with a common interface for each device.
.
So a
.I groff
postprocessor must only redefine the methods of this class.
.
For details,
see the reference in section \[lq]Files\[rq] below.
.
.
.\" ====================================================================
.SH Example
.\" ====================================================================
.
This section presents the
.I intermediate output
generated from the same input for three different devices.
.
The input is the sentence
.I hell world
fed into
.I groff
on the command line.
.
.
.IP \[bu] 2m
High-resolution device
.I ps
.
.
.RS
.P
.EX
.RB "shell>\~" "echo \[dq]hell world\[dq] | groff \-Z \-T ps"
.EE
.
.
.P
.EX
x T ps
x res 72000 1 1
x init
p1
x font 5 TR
f5
s10000
V12000
H72000
thell
wh2500
tw
H96620
torld
n12000 0
x trailer
V792000
x stop
.EE
.RE
.
.
.P
This output can be fed into the postprocessor
.MR grops @MAN1EXT@
to get its representation as a PostScript file, or
.MR gropdf @MAN1EXT@
to output directly to PDF.
.
.
.IP \[bu] 2m
Low-resolution device
.I latin1
.
.
.RS
.P
This is similar to the high-resolution device except that the
positioning is done at a minor scale.
.
Some comments (lines starting with
.IR # )
were added for clarification; they were not generated by the
formatter.
.
.
.P
.EX
\fBshell>\fP "hell world" | groff \-Z \-T latin1
.EE
.
.
.P
.EX
.I # prologue
x T latin1
x res 240 24 40
x init
.I # begin a new page
p1
.I # font setup
x font 1 R
f1
s10
.I # initial positioning on the page
V40
H0
.I # write text \[aq]hell\[aq]
thell
.I # inform about a space, and do it by a horizontal jump
wh24
.I # write text \[aq]world\[aq]
tworld
.I # announce line break, but do nothing because ...
n40 0
.I # ... the end of the document has been reached
x trailer
V2640
x stop
.EE
.RE
.
.
.P
This output can be fed into the postprocessor
.MR grotty @MAN1EXT@
to get a formatted text document.
.
.
.IP \[bu] 2m
Classical style output
.
.
.RS
.P
As a computer monitor has a very low resolution compared to modern
printers the
.I intermediate output
for the X\~devices can use the jump-and-write command with its 2-digit
displacements.
.
.
.P
.EX
\fBshell>\fP "hell world" | groff \-Z \-T X100
.EE
.
.
.P
.EX
x T X100
x res 100 1 1
x init
p1
x font 5 TR
f5
s10
V16
H100
.I # write text with old-style jump-and-write command
ch07e07l03lw06w11o07r05l03dh7
n16 0
x trailer
V1100
x stop
.EE
.RE
.
.
.P
This output can be fed into the postprocessor
.MR xditview 1x
or
.MR gxditview @MAN1EXT@
for displaying in\~X.
.
.
.P
Due to the obsolete jump-and-write command, the text clusters in the
classical output are almost unreadable.
.
.
.\" ====================================================================
.SH Compatibility
.\" ====================================================================
.
The
.I intermediate output
language of the
.I classical troff
was first documented in
[CSTR\~#97].
.
The
.I groff intermediate output
format is compatible with this specification except for the following
features.
.
.
.IP \[bu] 2m
The classical quasi device independence is not yet implemented.
.
.
.IP \[bu] 2m
The old hardware was very different from what we use today.
.
So the
.I groff
devices are also fundamentally different from the ones in
.I classical
.IR troff .
.
For example, the classical PostScript device was called
.I post
and had a resolution of 720 units per inch,
while
.IR groff 's
.I ps
device has a resolution of 72000 units per inch.
.
Maybe, by implementing some rescaling mechanism similar to the
classical quasi device independence, these could be integrated into
modern
.IR groff .
.
.
.IP \[bu] 2m
The B-spline command
.B D\[ti]
is correctly handled by the
.I intermediate output
parser, but the drawing routines aren't implemented in some of the
postprocessor programs.
.
.
.IP \[bu] 2m
The argument of the commands
.B s
and
.B x H
has the implicit unit scaled point\~\c
.B z
in
.IR groff ,
while
.I classical troff
had point (\c
.BR p ).
.
This isn't an incompatibility, but a compatible extension, for both
units coincide for all devices without a
.I sizescale
parameter, including all classical and the
.I groff
text devices.
.
The few
.I groff
devices with a sizescale parameter either did not exist, had a
different name, or seem to have had a different resolution.
.
So conflicts with classical devices are very unlikely.
.
.
.ie \n[@STUPID_DRAWING_POSITIONING]=1 \{\
.IP \[bu] 2m
The position changing after the commands
.BR Dp ,
.BR DP ,
and
.B Dt
is illogical, but as old versions of groff used this feature it is
kept for compatibility reasons.
.\}             \" @STUPID_DRAWING_POSITIONING
.el \{\
.IP \[bu] 2m
Temporarily, there existed some confusion on the positioning after the
.B D
commands that are
.I groff
extensions.
.
This has been clarified by establishing the classical rule for all
groff drawing commands:
.
.
.RS
.P
.ft I
The position after a graphic object has been drawn is at its end;
for circles and ellipses, the "end" is at the right side.
.ft
.RE
.
.
.P
From this, the positionings specified for the drawing commands above
follow quite naturally.
.\}             \" @STUPID_DRAWING_POSITIONING
.
.P
The differences between
.I groff
and
.I classical troff
are documented in
.MR groff_diff @MAN7EXT@ .
.
.
.\" ====================================================================
.SH Files
.\" ====================================================================
.
.TP
.IR @FONTDIR@/\:\%dev name /\:DESC
describes the output device
.IR name .
.
.
.br
.ne 4v
.\" ====================================================================
.SH Authors
.\" ====================================================================
.
James Clark wrote an early version of this document,
which described only the differences between AT&T
device-independent
.IR troff 's
output format and that of GNU
.IR roff .
.
The present version was completely rewritten in 2001 by
.MT groff\-bernd\:.warken\-72@\:web\:.de
Bernd Warken
.ME .
.
.
.\" ====================================================================
.SH "See also"
.\" ====================================================================
.
.P
.IR "Groff: The GNU Implementation of troff" ,
by Trent A.\& Fisher and Werner Lemberg,
is the primary
.I groff
manual.
.
You can browse it interactively with \[lq]info groff\[rq].
.
.
.P
\[lq]Troff User's Manual\[rq]
by Joseph F.\& Ossanna,
1976
(revised by Brian W.\& Kernighan,
1992),
AT&T Bell Laboratories Computing Science Technical Report No.\& 54,
widely called simply \[lq]CSTR\~#54\[rq],
documents the language,
device and font description file formats,
and device-independent output format
referred to collectively in
.I groff
documentation as
.RI \[lq]AT&T\~ troff \[rq].
.
.
.P
\[lq]A Typesetter-independent TROFF\[rq]
by Brian W.\& Kernighan,
1982,
AT&T Bell Laboratories Computing Science Technical Report No.\& 97,
provides additional insights into the
device and font description file formats
and device-independent output format.
.
.
.TP
.MR groff @MAN1EXT@
documents the
.B \-Z
option and contains pointers to further
.I groff
documentation.
.
.
.TP
.MR groff @MAN7EXT@
describes the
.I groff
language,
including its escape sequences and system of units.
.
.
.TP
.MR groff_font @MAN5EXT@
details the device scaling parameters of device
.I DESC
files.
.
.
.TP
.MR @g@troff @MAN1EXT@
generates the device-independent intermediate output documented here.
.
.
.TP
.MR roff @MAN7EXT@
presents historical aspects and the general structure of
.I roff
systems.
.
.
.TP
.MR groff_diff @MAN7EXT@
enumerates differences between the intermediate output produced by AT&T
.I troff \" AT&T
and that of
.IR groff .
.
.
.TP
.MR gxditview @MAN1EXT@
is a viewer for intermediate output.
.
.
.TP
.UR https://\:github.com/\:Alhadis/\:Roff\:.js/
.I Roff.js
.UE
is a viewer for intermediate output written in JavaScript.
.
.
.P
.MR grodvi @MAN1EXT@ ,
.MR grohtml @MAN1EXT@ ,
.MR grolbp @MAN1EXT@ ,
.MR grolj4 @MAN1EXT@ ,
.MR gropdf @MAN1EXT@ ,
.MR grops @MAN1EXT@ ,
and
.MR grotty @MAN1EXT@
are
.I groff
postprocessors.
.
.
.\" Restore compatibility mode (for, e.g., Solaris 10/11).
.cp \n[*groff_groff_out_5_man_C]
.do rr *groff_groff_out_5_man_C
.
.
.\" Local Variables:
.\" fill-column: 72
.\" mode: nroff
.\" End:
.\" vim: set filetype=groff textwidth=72: