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.TH GROFF_FONT @MAN5EXT@ "@MDATE@" "Groff Version @VERSION@"
.
.
.SH NAME
groff_font \- format of groff device and font description files
.
.
.SH DESCRIPTION
The groff font format is roughly a superset of the ditroff
font format.
.
The font files for device
.I name
are stored in a directory
.BI dev name\c
\&.
.
There are two types of file: a
device description file called
.B DESC
and for each font
.I F
a font file called
.IR F .
.
These are text files;
unlike the ditroff font format,
there is no associated binary format.
.
.
.SS DESC file format
.
The DESC file can contain the following types of line as shown below.
.
Later entries in the file override previous values.
.
.TP
.B charset
This line and everything following in the file are ignored.
.
It is allowed for the sake of backwards compatibility.
.
.TP
.BI family\  fam
The default font family is
.IR fam .
.
.TP
.BI fonts\  n\ F1\ F2\ F3\|.\|.\|.\|Fn
Fonts
.I F1\|.\|.\|.\|Fn
will be mounted in the font positions 
.IR m +1,\|.\|.\|., m + n
where
.I m
is the number of styles.
.
This command may extend over more than one line.
.
A font name of
.B 0
will cause no font to be mounted on the corresponding font position.
.
.TP
.BI hor\  n
The horizontal resolution is
.I n
machine units.
.
.TP
.BI image_generator\  string
Needed for
.B grohtml
only.
It specifies the program to generate PNG images from
PostScript input.
Under GNU/Linux this is usually
.I gs
but under other systems (notably cygwin) it might be set to another name.
.
.TP
.BI paperlength\  n
The physical vertical dimension of the output medium in machine units.
.
This isn't used by
.B troff
itself but by output devices.
.
Deprecated.
.
Use
.B papersize
instead.
.
.TP
.BI papersize\  string
Select a paper size.
.
Valid values for
.I string
are the ISO paper types A0-A7, B0-B7, C0-C7, D0-D7, DL, and the US paper
types letter, legal, tabloid, ledger, statement, executive, com10, and
monarch.
.
Case is not significant for
.IR string
if it holds predefined paper types.
.
Alternatively,
.I string
can be a file name (e.g.\& `/etc/papersize'); if the file can be opened,
.B groff
reads the first line and tests for the above paper sizes.
.
Finally,
.I string
can be a custom paper size in the format
.IB length , width
(no spaces before and after the comma).
.
Both
.I length
and
.I width
must have a unit appended; valid values are `i' for inches, `c' for
centimeters, `p' for points, and `P' for picas.
.
Example:
.BR 12c,235p .
.
An argument which starts with a digit is always treated as a custom paper
format.
.
.B papersize
sets both the vertical and horizontal dimension of the output medium.
.
.IP
More than one argument can be specified;
.B groff
scans from left to right and uses the first valid paper specification.
.
.TP
.BI paperwidth\  n
The physical horizontal dimension of the output medium in machine units.
.
Deprecated.
.
Use
.B papersize
instead.
.
This isn't used by
.BR troff
itself but by output devices.
.
.TP
.B pass_filenames
Make troff tell the driver the source file name being processed.
.
This is achieved by another tcommand:
.B F
.IR filename .
.
.TP
.BI postpro\  program
Use
.I program
as the postprocessor.
.
.TP
.BI prepro\  program
Call
.I program
as a preprocessor.
.
.TP
.BI print\  program
Use
.I program
as the spooler program for printing.
.
If omitted, the
.B \-l
and
.B \-L
options of
.B groff
are ignored.
.
.TP
.BI res\  n
There are
.I n
machine units per inch.
.
.TP
.BI sizes\  s1\ s2\|.\|.\|.\|sn\  0
This means that the device has fonts at
.IR s1 ,
.IR s2 ,\|.\|.\|.\| sn
scaled points.
.
The list of sizes must be terminated by a
.BR 0 .
.
Each
.I si
can also be a range of sizes
.IR m \- n .
.
The list can extend over more than one line.
.
.TP
.BI sizescale\  n
The scale factor for pointsizes.
.
By default this has a value of 1.
.
One
.I
scaled point
is equal to
one
.RI point/ n .
.
The arguments to the
.B unitwidth
and
.B sizes
commands are given in scaled points.
.
.TP
.BI styles\  S1\ S2\|.\|.\|.\|Sm
The first
.I m
font positions will be associated with styles
.IR S1\|.\|.\|.\|Sm .
.
.TP
.B tcommand
This means that the postprocessor can handle the
.B t
and
.B u
output commands.
.
.TP
.BI unitwidth\  n
Quantities in the font files are given in machine units
for fonts whose point size is
.I n 
scaled points.
.
.TP
.B unscaled_charwidths
Make the font handling module always return unscaled character widths.
Needed for the
.B grohtml
device.
.
.TP
.B use_charnames_in_special
This command indicates that troff should encode named characters inside
special commands.
.
.TP
.BI vert\  n
The vertical resolution is
.I n
machine units.
.
.LP
The
.BR res ,
.BR unitwidth ,
.BR fonts ,
and
.B sizes
lines are compulsory.
.
Not all commands in the DESC file are used by
.B troff
itself; some of the keywords (or even additional ones) are used by
postprocessors to store arbitrary information about the device.
.
.LP
Here a list of obsolete keywords which are recognized by
.B groff
but completely ignored:
.BR spare1 ,
.BR spare2 ,
.BR biggestfont .
.
.
.SS Font file format
.
A font file has two sections.
The first section is a sequence
of lines each containing a sequence of blank delimited
words; the first word in the line is a key, and subsequent
words give a value for that key.
.
.TP
.BI ligatures\  lig1\ lig2\|.\|.\|.\|lign\ \fR[ 0 \fR]
Characters
.IR lig1 ,
.IR lig2 ,\ \|.\|.\|.,\ lign
are ligatures; possible ligatures are
.BR ff ,
.BR fi ,
.BR fl ,
.B ffi
and
.BR ffl .
.
For backwards compatibility, the list of ligatures may be terminated
with a
.BR 0.
.
The list of ligatures may not extend over more than one line.
.
.TP
.BI name\  F
The name of the font is
.IR F .
.
.TP
.BI slant\  n
The characters of the font have a slant of
.I n
degrees.
.
(Positive means forward.)
.
.TP
.BI spacewidth\  n
The normal width of a space is
.IR n .
.
.TP
.B special
The font is
.IR special ;
this means that when a character is requested that is not present in
the current font, it will be searched for in any special fonts that
are mounted.
.
.LP
Other commands are ignored by
.B troff
but may be used by postprocessors to store arbitrary information
about the font in the font file.
.
.LP
The first section can contain comments which start with the
.B #
character and extend to the end of a line.
.
.LP
The second section contains one or two subsections.
.
It must contain a
.I charset
subsection
and it may also contain a
.I kernpairs
subsection.
.
These subsections can appear in any order.
.
Each subsection starts with a word on a line by itself.
.
.LP
The word
.B charset
starts the charset subsection.
.
The
.B charset
line is followed by a sequence of lines.
.
Each line gives information for one character.
.
A line comprises a number of fields separated
by blanks or tabs.
.
The format is
.
.IP
.I name metrics type code 
.RI [ entity_name ]
.RB [ --
.IR comment ]
.
.LP
.I name
identifies the character:
if
.I name
is a single character
.I c
then it corresponds to the groff input character
.IR c ;
if it is of the form
.BI \[rs] c
where c is a single character, then it
corresponds to the special character
.BI \[rs][ c ]\fR;
otherwise it corresponds to the groff input character
.BI \[rs][ name ]\fR.
.
If it is exactly two characters
.I xx
it can be entered as
.BI \[rs]( xx\fR.
.
Note that single-letter special characters can't be accessed as
.BI \[rs] c\fR;
the only exception is `\[rs]-' which is identical to `\[rs][-]'.
.
The name
.B \-\-\-
is special and indicates that the character is unnamed;
such characters can only be used by means of the
.B \[rs]N
escape sequence in
.BR troff .
.
.LP
Groff supports eight-bit characters; however some utilities
have difficulties with eight-bit characters.
.
For this reason, there is a convention that the name
.BI char n
is equivalent to the single character whose code is
.IR n .
.
For example,
.B char163
would be equivalent to the character with code 163
which is the pounds sterling sign in ISO Latin-1.
.
.LP
The
.I type
field gives the character type:
.
.TP
1
means the character has a descender, for example, p;
.
.TP
2
means the character has an ascender, for example, b;
.
.TP
3
means the character has both an ascender and a descender, for example,
(.
.
.LP
The
.I code
field gives the code which the postprocessor uses to print the character.
.
The character can also be input to groff using this code by means of the
.B \[rs]N
escape sequence.
.
The code can be any integer.
.
If it starts with a
.B 0
it will be interpreted as octal;
if it starts with
.B 0x
or
.B 0X
it will be intepreted as hexadecimal.
.
Note, however, that the
.B \[rs]N
escape sequence only accepts a decimal integer.
.
.LP
The
.I entity_name
field gives an ascii string identifying the glyph which the postprocessor
uses to print the character.
.
This field is optional and has been introduced so that the html device driver
can encode its character set.
.
For example, the character `\[rs][Po]' is represented as `£' in
html\~4.0.
.
.LP
Anything on the line after the encoding field resp. after `-\&-' will
be ignored.
.
.LP
The
.I metrics
field has the form (in one line; it is broken here for the sake of
readability):
.
.IP
.I width\c
.RI [\fB, height\c
.RI [\fB, depth\c
.RI [\fB, italic-correction
.br
.RI [\fB, left-italic-correction\c
.RI [\fB, subscript-correction ]]]]]
.
.LP
There must not be any spaces between these subfields.
.
Missing subfields are assumed to be 0.
.
The subfields are all decimal integers.
.
Since there is no associated binary format, these
values are not required to fit into a variable of type
.B char
as they are in ditroff.
.
The
.I width
subfields gives the width of the character.
.
The
.I height
subfield gives the height of the character (upwards is positive);
if a character does not extend above the baseline, it should be
given a zero height, rather than a negative height.
.
The
.I depth
subfield gives the depth of the character, that is, the distance
below the lowest point below the baseline to which the
character extends (downwards is positive);
if a character does not extend below above the baseline, it should be
given a zero depth, rather than a negative depth.
.
The
.I italic-correction
subfield gives the amount of space that should be added after the
character when it is immediately to be followed by a character
from a roman font.
.
The
.I left-italic-correction
subfield gives the amount of space that should be added before the
character when it is immediately to be preceded by a character
from a roman font.
.
The
.I subscript-correction
gives the amount of space that should be added after a character
before adding a subscript.
.
This should be less than the italic correction.
.
.LP
A line in the charset section can also have the format
.
.IP
.I
name \fB"
.
.LP
This indicates that
.I name
is just another name for the character mentioned in the
preceding line.
.
.LP
The word
.B kernpairs
starts the kernpairs section.
.
This contains a sequence of lines of the form:
.
.IP
.I c1 c2 n
.
.LP
This means that when character
.I c1
appears next to character
.I c2
the space between them should be increased by
.IR n .
.
Most entries in kernpairs section will have a negative value for
.IR n .
.
.
.SH FILES
.
.Tp \w'@FONTDIR@/devname/DESC'u+3n
.BI @FONTDIR@/dev name /DESC
Device description file for device
.IR name .
.
.TP
.BI @FONTDIR@/dev name / F
Font file for font
.I F
of device
.IR name .
.
.
.SH "SEE ALSO"
.
.BR groff_out (@MAN5EXT@),
.BR @g@troff (@MAN1EXT@).
.
.cp \n[groff_font_C]
.
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