[AD] interpolating rotation routines

[David Kühling <dkuelhin@xxxxxxxxxx>]

Hallo!

Some days ago I created a set of sprite rotation routines that use
bilinear
interpolation for smoothing the pictures. After 4 days of optimizing
they're
now so fast that my game can actually use them. According to what my
test
program says they have about 40% the speed of the original routines.
That test
program (`exrot_i.c') and the rotation routines are included in the
attached
archive. The makefile should compile them in dos and Unix.  If you like
to add
these routines to the Allegro library, just add the few `AL_FUNC' lines
from
`rotate_i.h' to `allegro.h' and concatenate the contents of `rotate_i.c'
to
Allegro's `src/rotate.c'. Please note that the interpolation is
performed on
RGB values rather than HSV. This is many times faster but it's not
perfect.
Very high contrast pictures may be displayed a little incorrectly.
Another
point to mention is, that edges between transparent pixels and
non-transparent
pixels are smoothed by interpolating with the background pixels. This
kind of
smoothing is not done at the sprite's borders. That's why sprites which
need
smooth edges should be surrounded by a border of transparent pixels.
This
method is necessary to make it possible to use rotated sprites for
tiling.

During development I noticed that `makecol' sometimes returns strange
colors
in 8bit mode. Try the program `maybebug.c', included in the attached
archive
and you'll see what I mean. That program tries to generate gradients
from red,
green and blue to white. For some reason the blue->white gradient
contains
some very dark colors. Note that I'm using Allegro version 3.9.30 (WIP).

Bye,	
							David Kühling

Attachment: rotate_ip.tar.gz
Description: GNU Zip compressed data