Provided by: sam_4.3-18.2_i386
bitmap - external format for bitmaps
#include <libc.h> #include <libg.h>
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
consists 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-
coordinate = 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 48×48 face files and 16×16 cursors,
are stored textually, suitable for inclusion in C source. Each line of
text represents one scan line as a comma-separated sequence of
hexadecimal 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.
graphics(3g), bitblt(3g), balloc(3g), font(5g)