groff_font - format of groff device and font description files
The groff font format is roughly a superset of the ditroff font format.
The font files for device name are stored in a directory devname.
There are two types of file: a device description file called DESC and
for each font F a font file called F. These are text files; unlike the
ditroff font format, there is no associated binary format.
DESC file format
The DESC file can contain the following types of line as shown below.
Later entries in the file override previous values.
Empty lines are ignored.
This line and everything following in the file are ignored. It
is allowed for the sake of backwards compatibility.
The default font family is fam.
fonts n F1 F2 F3 ... Fn
Fonts F1, ..., Fn are mounted in the font positions
m+1, ..., m+n where m is the number of styles. This command may
extend over more than one line. A font name of 0 causes no font
to be mounted on the corresponding font position.
hor n The horizontal resolution is n machine units.
Needed for grohtml only. It specifies the program to generate
PNG images from PostScript input. Under GNU/Linux this is
usually gs but under other systems (notably cygwin) it might be
set to another name.
The physical vertical dimension of the output medium in machine
units. This isn’t used by troff itself but by output devices.
Deprecated. Use papersize instead.
Select a paper size. Valid values for 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 string if it holds
predefined paper types. Alternatively, string can be a file
name (e.g. ‘/etc/papersize’); if the file can be opened, groff
reads the first line and tests for the above paper sizes.
Finally, string can be a custom paper size in the format
length,width (no spaces before and after the comma). Both
length and width must have a unit appended; valid values are ‘i’
for inches, ‘c’ for centimeters, ‘p’ for points, and ‘P’ for
picas. Example: 12c,235p. An argument which starts with a
digit is always treated as a custom paper format. papersize
sets both the vertical and horizontal dimension of the output
More than one argument can be specified; groff scans from left
to right and uses the first valid paper specification.
The physical horizontal dimension of the output medium in
machine units. Deprecated. Use papersize instead. This isn’t
used by troff itself but by output devices.
Make troff tell the driver the source file name being processed.
This is achieved by another tcommand: F filename.
Use program as the postprocessor.
Call program as a preprocessor.
Use program as the spooler program for printing. If omitted,
the -l and -L options of groff are ignored.
res n There are n machine units per inch.
sizes s1 s2 ... sn 0
This means that the device has fonts at s1, s2, ..., sn scaled
points. The list of sizes must be terminated by a 0. Each si
can also be a range of sizes m-n. The list can extend over more
than one line.
The scale factor for point sizes. By default this has a value
of 1. One scaled point is equal to one point/n. The arguments
to the unitwidth and sizes commands are given in scaled points.
styles S1 S2 ... Sm
The first m font positions are associated with styles
S1, ..., Sm.
This means that the postprocessor can handle the t and u output
Indicate that the output device supports the complete Unicode
repertoire. Useful only for devices which produce character
entities instead of glyphs.
If unicode is present, no charset section is required in the
font description files since the Unicode handling built into
groff is used. However, if there are entries in a charset
section, they either override the default mappings for those
particular characters or add new mappings (normally for
This is used for -Tutf8, -Thtml, and -Txhtml.
Quantities in the font files are given in machine units for
fonts whose point size is n scaled points.
Make the font handling module always return unscaled glyph
widths. Needed for the grohtml device.
This command indicates that troff should encode named glyphs
inside special commands.
vert n The vertical resolution is n machine units.
The res, unitwidth, fonts, and sizes lines are compulsory. Not all
commands in the DESC file are used by troff itself; some of the
keywords (or even additional ones) are used by postprocessors to store
arbitrary information about the device.
Here a list of obsolete keywords which are recognized by groff but
completely ignored: spare1, spare2, biggestfont.
Font file format
A font file has two sections; empty lines are ignored in both of them.
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.
ligatures lig1 lig2 ... lign 
Glyphs lig1, lig2, ..., lign are ligatures; possible ligatures
are ff, fi, fl, ffi, and ffl. For backwards compatibility, the
list of ligatures may be terminated with a 0. The list of
ligatures may not extend over more than one line.
name F The name of the font is F.
The glyphs of the font have a slant of n degrees. (Positive
The normal width of a space is n.
The font is special; this means that when a glyph is requested
that is not present in the current font, it is searched for in
any special fonts that are mounted.
Other commands are ignored by troff but may be used by postprocessors
to store arbitrary information about the font in the font file.
The first section can contain comments which start with the # character
and extend to the end of a line.
The second section contains one or two subsections. It must contain a
charset subsection and it may also contain a kernpairs subsection.
These subsections can appear in any order. Each subsection starts with
a word on a line by itself.
The word charset starts the charset subsection. The charset line is
followed by a sequence of lines. Each line gives information for one
glyph. A line comprises a number of fields separated by blanks or
tabs. The format is
name metrics type code [entity_name] [-- comment]
name identifies the glyph: if name is a single glyph c then it
corresponds to the groff input character c; if it is of the form \c
where c is a single character, then it corresponds to the special
character \[c]; otherwise it corresponds to the groff input character
\[name]. If it is exactly two characters xx it can be entered as \(xx.
Note that single-letter special characters can’t be accessed as \c; the
only exception is ‘\-’ which is identical to ‘\[-]’. The name --- is
special and indicates that the glyph is unnamed; such glyphs can only
be used by means of the \N escape sequence in troff.
The type field gives the glyph type:
1 means the glyph has a descender, for example, ‘p’;
2 means the glyph has an ascender, for example, ‘b’;
3 means the glyph has both an ascender and a descender, for
The code field gives the code which the postprocessor uses to print the
glyph. The glyph can also be input to groff using this code by means
of the \N escape sequence. The code can be any integer. If it starts
with a 0 it is interpreted as octal; if it starts with 0x or 0X it is
intepreted as hexadecimal. Note, however, that the \N escape sequence
only accepts a decimal integer.
The entity_name field gives an ASCII string identifying the glyph which
the postprocessor uses to print that glyph. This field is optional and
is currently used by grops to build sub-encoding arrays for PS fonts
containing more than 256 glyphs. (It has also been used for grohtml’s
entity names but for efficiency reasons this data is now compiled
directly into grohtml.)
Anything on the line after the encoding field or ‘--’ are ignored.
The metrics field has the form (in one line; it is broken here for the
sake of readability):
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 char as they are in ditroff.
The width subfields gives the width of the glyph. The height subfield
gives the height of the glyph (upwards is positive); if a glyph does
not extend above the baseline, it should be given a zero height, rather
than a negative height. The depth subfield gives the depth of the
glyph, that is, the distance below the lowest point below the baseline
to which the glyph extends (downwards is positive); if a glyph does not
extend below above the baseline, it should be given a zero depth,
rather than a negative depth. The italic-correction subfield gives the
amount of space that should be added after the glyph when it is
immediately to be followed by a glyph from a roman font. The left-
italic-correction subfield gives the amount of space that should be
added before the glyph when it is immediately to be preceded by a glyph
from a roman font. The subscript-correction gives the amount of space
that should be added after a glyph before adding a subscript. This
should be less than the italic correction.
A line in the charset section can also have the format
This indicates that name is just another name for the glyph mentioned
in the preceding line.
The word kernpairs starts the kernpairs section. This contains a
sequence of lines of the form:
c1 c2 n
This means that when glyph c1 appears next to glyph c2 the space
between them should be increased by n. Most entries in kernpairs
section have a negative value for n.
Device description file for device name.
Font file for font F of device name.