groff_font - format of groff device and font description files
DESCRIPTION
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.
charset
This line and everything following in the file are ignored.
It is allowed for the sake of backwards compatibility.
family fam
The default font family is
fam.
fonts n F1 F2 F3...Fn
Fonts
F1...Fn
will be 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
will cause no font to be mounted on the corresponding font position.
hor n
The horizontal resolution is
n
machine units.
paperheight n
The physical vertical dimension of the output medium in machine units.
This isn't used by
troff
itself; currently, only
grops
uses it.
paperwidth n
The physical horizontal dimension of the output medium in machine units.
This isn't used by
troff.
Currently, only the
grolbp
output device uses it.
papersize string
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 medium.
More than one argument can be specified;
groff
scans from left to right and uses the first valid paper specification.
pass_filenames
Make troff tell the driver the source file name being processed.
This is achieved by another tcommand:
Ffilename.
postpro program
Use
program
as the postprocessor.
prepro program
Call
program
as a preprocessor.
print program
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.
sizescale n
The scale factor for pointsizes.
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 will be associated with styles
S1...Sm.
tcommand
This means that the postprocessor can handle the
t
and
u
output commands.
unitwidth n
Quantities in the font files are given in machine units
for fonts whose point size is
n
scaled points.
use_charnames_in_special
This command indicates that troff should encode named characters inside
special commands.
vert n
The vertical resolution is
n
machine units.
The
res,
unitwidth,
fonts,
and
sizes
lines are compulsory.
Other commands are ignored by
troff
but may be used by postprocessors to store arbitrary information
about the device in the DESC file.
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.
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 [0]
Characters
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.
slant n
The characters of the font have a slant of
n
degrees.
(Positive means forward.)
spacewidth n
The normal width of a space is
n.
special
The font is
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.
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 character.
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 character:
if
name
is a single character
c
then it corresponds to the groff input character
c;
if it is of the form
[rs]c
where c is a single character, then it
corresponds to the special character
[rs][c];
otherwise it corresponds to the groff input character
[rs][name].
If it is exactly two characters
xx
it can be entered as
[rs](xx.
Note that single-letter special characters can't be accessed as
[rs]c;
the only exception is `[rs]-' which is identical to `[rs][-]'.
The name
---
is special and indicates that the character is unnamed;
such characters can only be used by means of the
[rs]N
escape sequence in
troff.
Groff supports eight-bit characters; however some utilities
have difficulties with eight-bit characters.
For this reason, there is a convention that the name
charn
is equivalent to the single character whose code is
n.
For example,
char163
would be equivalent to the character with code 163
which is the pounds sterling sign in ISO Latin-1.
The
type
field gives the character type:
1
means the character has a descender, for example, p;
2
means the character has an ascender, for example, b;
3
means the character has both an ascender and a descender, for example,
(.
The
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
[rs]N
escape sequence.
The code can be any integer.
If it starts with a
0
it will be interpreted as octal;
if it starts with
0x
or
0X
it will be intepreted as hexadecimal.
Note, however, that the
[rs]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 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.
Anything on the line after the encoding field resp. after `--' will
be 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 character.
The
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
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
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
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
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.
A line in the charset section can also have the format
name "
This indicates that
name
is just another name for the character 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 character
c1
appears next to character
c2
the space between them should be increased by
n.
Most entries in kernpairs section will have a negative value for
n.
FILES
u+3n
/usr/share/groff/1.18.1.1/font/devname/DESC
Device description file for device
name.
