BITMAP(7g) BITMAP(7g)
NAME
bitmap - external format for bitmaps
SYNOPSIS
#include <libc.h> #include <libg.h>
DESCRIPTION
Bitmaps are described in graphics(3g). Fonts and bitmaps are stored in
external files in machine-independent formats.
Bitmap files are read and written using rdbitmapfile and wrbitmapfile
(see balloc(3g)). A bitmap file starts with 5 decimal strings: ldepth,
r.min.x, r.min.y, r.max.x, and r.max.y. Each number is right-justified
and blank padded in 11 characters, followed by a blank. The rest of
the file contains the r.max.y-r.min.y rows of bitmap data. A row con-
sists of the byte containing pixel r.min.x and all the bytes up to and
including the byte containing pixel r.max.x-1. A pixel with x-coordi-
nate = x in a bitmap with ldepth = l will appear as w = 2^l contiguous
bits in a byte, with the pixel's high order bit starting at the byte's
bit number w*(x mod 8/w), where bits within a byte are numbered 0 to 7
from the high order to the low order bit. If w is greater than 8, it
is a multiple of 8, so pixel values take up an integral number of
bytes. Rows contain integral number of bytes, so there may be some
unused pixels at either end of a row.
The rdbitmap and wrbitmap functions described in balloc(3g) also deal
with rows in this format, stored in user memory.
Some small images, in particular 48x48 face files and 16x16 cursors,
are stored textually, suitable for inclusion in C source. Each line of
text represents one scan line as a comma-separated sequence of hexadec-
imal bytes, shorts, or words in C format. For cursors, each line
defines a pair of bytes. (It takes two images to define a cursor; each
must be stored separately.) Face files of one bit per pixel are stored
as a sequence of shorts, those of larger pixel sizes as a sequence of
longs. Software that reads these files must deduce the image size from
the input; there is no header. These formats reflect history rather
than design.
SEE ALSO
graphics(3g), bitblt(3g), balloc(3g), font(5g)
BITMAP(7g)
