Fonts and subfonts are described in
External fonts are described by a plain text file that can be read using
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
The minimum number of a covered range is mapped to the specified starting position
(default zero) of the
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.
External subfonts are represented in a more rigid format
that can be read and written using
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
The subfont header has 3
ascent. Each number is right-justified and blank padded in 11 characters, followed by a blank.
info consists of
n+1 6-byte entries, each giving the
x (2 bytes, low order byte first),
x field of the last
Fontchar is used to calculate the image width
of the previous character; the other fields in the last
Fontchar are irrelevant.
Note that the convention of using the character with value zero (NUL) to represent
characters of zero width (see
means that fonts should have, as their zeroth character,
one with non-zero width.