BITMAP(6) Games Manual BITMAP(6)
bitmap - external format for bitmaps
Bitmaps are described in graphics(2). Fonts and bitmaps are stored in
external files in machine-independent formats.
Bitmap files are read and written using rdbitmapfile and wrbitmapfile
(see balloc(2)). 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 = ld will appear as w = 2^ld contigu-
ous 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 num-
bered 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 num-
ber 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(2) also deal
with rows in this format, stored in user memory.
Some small images, in particular 48x48 face files as used by seemail
(see mail(1)) and 16x16 cursors, can be 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 to be pro-
cessed by programs such as tweak(1).) 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.
tweak(1), graphics(2), bitblt(2), balloc(2), face(6), font(6)