harvey/sys/man/6/font

.TH FONT 6
.SH NAME
font, subfont \- external format for fonts and subfonts
.SH SYNOPSIS
.B #include <libg.h>
.SH DESCRIPTION
Fonts and subfonts are described in
.IR cachechars (2).
.PP
External fonts are described by a plain text file that can be read using
.IR openfont .
The format of the file is a header followed by any number of
subfont range specifications.
The header contains two numbers: the height and the ascent, both in pixels.
The height is the inter-line spacing and the ascent is the distance
from the top of the line to the baseline.  These numbers are chosen
to display consistently all the subfonts of the font.
A subfont range specification contains two or three numbers and a file name.
The numbers are the inclusive range of characters covered by the subfont,
with an optional starting position within the subfont,
and the file name names an external file suitable for
.I readsubfont
(see
.IR graphics (2)).
The minimum number of a covered range is mapped to the specified starting position
(default zero) of the
corresponding subfont.
If the subfont file name does not begin with a slash, it is taken relative to the
directory containing the font file.
Each field must be followed by some white space.
Each numeric field may be C-format decimal, octal, or hexadecimal.
.PP
External subfonts are represented in a more rigid format
that can be read and written using
.I readsubfont
and
.I writesubfont
(see
.IR subfont (2)).
The format for subfont files is: an image containing character glyphs,
followed by a subfont header, followed by character information.
The image has the format for external image files described in
.IR image (6).
The subfont header has 3
decimal strings:
.BR n ,
.BR height ,
and
.BR ascent .
Each number is right-justified and blank padded in 11 characters, followed by a blank.
The character
.B info
consists of
.BR n +1
6-byte entries, each giving the
.B Fontchar
.B x
(2 bytes, low order byte first),
.BR top ,
.BR bottom ,
.BR left ,
and
.BR width .
The
.B x
field of the last
.B Fontchar
is used to calculate the image width
of the previous character; the other fields in the last
.B Fontchar
are irrelevant.
.PP
Note that the convention of using the character with value zero (NUL) to represent
characters of zero width (see
.IR draw (2))
means that fonts should have, as their zeroth character,
one with non-zero width.
.SH FILES
.TF /lib/font/bit/*
.TP
.B /lib/font/bit/*
font directories
.SH "SEE ALSO"
.IR graphics (2),
.IR draw (2),
.IR cachechars (2),
.IR subfont (2)