Just for grins I did some benchmarking on using convert_alpha() and
RLEACCEL. These are blitting a 32bpp 70x70 surface with per pixel
alpha on a 2GHz MacBook pro with pygame 1.7 and SDL 1.2.11.
I used the python timeit module, and blitted the image 100k times on
an 800x600 32bpp SW screen surface (default flags). These times are
averaged over several runs.
Time to blit unoptimized (straight from image.load):
23.7 sec
Time to blit with convert_alpha():
3.0 sec
Time to blit with convert_alpha() and set_alpha(0, pygame.RLEACCEL):
2.8 sec
This is just one image which has large areas that are completely
transparent and completely opaque and blended transparency around the
edges.
For grins I also tried it with a fullscreen surface (FULLSCREEN |
HWSURFACE | DOUBLEBUF) (which on macosx is a sw surface, but I use
the HWSURFACE flag hack to get SDL to use its experimental high perf
fullscreen macosx mode). The results are generally faster, but the
lesson is the same:
no optimization: 22.0 sec
convert_alpha() only: 2.7 sec
convert_alpha() and RLEACCEL: 2.0 sec
So convert_alpha() is a huge win, and RLEACCEL is some icing on the
cake. Granted this is just one example image, but I thought it was
worth sharing.
-Casey
On Sep 14, 2007, at 2:05 AM, Ulf Ekström wrote:
If you do software surface blitting you can speed up the alpha
blending a lot by using RLE encoding of the transparent surface. I
suppose there is special code in there for the case of completely
transparent or completely opaque pixels. You can use it with by doing
something like surface.set_alpha(0, pygame.RLEACCEL), but I must admit
I have only used this with the C SDL functions, so perhaps someone can
fill in the details. The '0' is ignored when the the surface has per
pixel alpha.
Transparent edges of sprites really look much much better than hard
edges, compare for example
http://offload2.icculus.org/airstrike/screenshots/ohmygod.png (no
alpha)
with
http://offload2.icculus.org/airstrike/screenshots/screenshot5.png (per
pixel alpha)
You can generate the soft edges by asking your artist to draw the
sprites in high resolution, on a transparent background, and then
scale them down.
Regards,
Ulf
