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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.
Unlike the ditroff font format, there is no associated binary
format.
The font files for device
.I name
are stored in a directory
.BI dev name.
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;
there is no associated binary format.
.SS DESC file format
The DESC file can contain the following types of line:
.TP
.BI res\  n
There are
.I n
machine units per inch.
.TP
.BI hor\  n
The horizontal resolution is
.I n
machine units.
.TP
.BI vert\  n
The vertical resolution is
.I n
machine units.
.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 unitwidth\  n
Quantities in the font files are given in machine units
for fonts whose point size is
.I n 
scaled points.
.TP
.B tcommand
This means that the postprocessor can handle the
.B t
and
.B u
output commands.
.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
.BI s i
can also be a range of sizes
.IR m \- n .
The list can extend over more than one line.
.TP
.BI styles\  S1\ S2\|.\|.\|.\|Sm
The first
.I m
font positions will be associated with styles
.IR S1\|.\|.\|.\|Sm .
.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 family\  fam
The default font family is
.IR fam .
.TP
.B charset
This line and everything following in the file are ignored.
It is allowed for the sake of backwards compatibility.
.LP
The res, unitwidth, fonts and sizes lines are compulsory.
Other commands are ignored by
.B troff
but may be used by postprocessors to store arbitrary information
about the device in the DESC file.
.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 name\  F
The name of the font is
.IR F .
.TP
.BI spacewidth\  n
The normal width of a space is
.IR n .
.TP
.BI slant\  n
The characters of the font have a slant of
.I n
degrees. (Positive means forward.)
.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 
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
.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 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 \e c
where c is a single character, then it
corresponds to the groff input character
.BI \e c\fR;
otherwise it corresponds to the groff input character
.BI \e[ name ]
(if it is exactly two characters
.I xx
it can be entered as
.BI \e( xx\fR.)
Groff supports eight bit characters; however some utilities
has 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
.I n .
For example,
.B char163
would be equivalent to the character with code 163
which is the pounds sterling sign in ISO Latin-1.
The name
.B \-\-\-
is special and indicates that the character is unnamed;
such characters can only be used by means of the
.B \eN
escape sequence in
.BR troff .
.LP
The
.I type
field gives the character type:
.TP
1
means the character has an 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 \eN
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.
.LP
Anything on the line after the code field will be ignored.
.LP
The
.I metrics
field has the form:
.IP
.IR width [\fB, height [\fB, depth [\fB, italic_correction [\fB, \
left_italic_correction [\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@).