subfalloc, subffree, rdsubfontfile, wrsubfontfile, mkfont - subfont manipulation
Subfont* subfalloc(int n, int height, int ascent,
Fontchar *info, Bitmap *b, ulong q0, ulong q1)
void subffree(Subfont *f)
Subfont* rdsubfontfile(int fd, Bitmap *b)
void wrsubfontfile(int fd, Subfont *f)
Font* mkfont(Subfont *f, Rune min);
Subfonts are the components of fonts that hold the character images. A font comprises an
array of subfonts; see cachechars(2). A new Subfont is allocated and initialized with
subfalloc. See cachechars(2) for the meaning of n, height, ascent, and info, and the
arrangement of characters in bitmap b. The fields of the returned Subfont structure are
set to the passed arguments, and the id field is set to the identifying number used by
/dev/bitblt (see bit(3)). After a successful subfalloc, b is attached to the subfont and
is unavailable to the application; it should not be used. Subfalloc returns 0 on failure.
The q0 and q1 arguments are used as tags in a cache of subfonts (see below). If all ones,
they disable caching.
Subffree frees a subfont and all its associated structure including the associated bitmap.
Since subffree calls free on f->info, if f->info was not allocated by malloc(2) it should
be zeroed before calling subffree.
A number of subfonts are kept in external files. The convention for naming subfont files
where size is approximately the height in pixels of the lower case letters (without ascen-
ders or descenders). If there is only one version of the subfont, the .ldepth extension
is elided. Class describes the range of runes encoded in the subfont: ascii, latin1,
The format of a subfont file is described in font(6)). Briefly, it contains a bitmap with
all the characters in it, followed by a subfont header, followed by character information.
Rdsubfontfile reads a subfont from the file descriptor fd. If b is zero, rdsubfontfile
reads the bitmap as well as the character information from the file and allows the result-
ing subfont and bitmap to be cached in the server for sharing with other applications.
The first thing such an rdsubfontfile call does is check to see if the subfont can be
recovered directly from the server: if the qid (see intro(5)) of the file pointed to by fd
matches q0 and q1 of a cache entry, the subfont is read from the server instead of from
fd. This is the normal use of rdsubfontfile.
Unusual applications such as font editors may choose to have uncached (hence unshared)
subfonts or to associate arbitrary bitmaps with the character data. If the b argument to
rdsubfontfile is non-null, rdsubfontfile reads only the character information from fd
(which must be positioned after the bitmap in the file) and the resulting subfont is
uncached. Nonetheless, rdsubfontfile calls subfalloc with b and hence b is unusable
afterwards; make a copy first if necessary. Rdsubfontfile returns 0 on error.
Wrsubfontfile writes on fd the part of a subfont file that comes after the bitmap.
Because the bitmap of a cached subfont is unavailable to the application, without extraor-
dinary measures only uncached subfonts may be written whole to files.
Mkfont takes as argument a Subfont s and returns a pointer to a Font that maps the charac-
ter images in s into the Runes min to min+s->n-1.
bitmap font file tree
graphics(2), balloc(2), bitblt(2), cachechars(2), bitmap(6), font(6)
All of the functions use the graphics error function (see graphics(2)).
Subfonts can contain no more than about 1300 characters.