Commit ID 7a2e0f7b30cb08905820efc1d53878e12674dac6
|Contributor:||Sam Lantinga||Files Modified:||1|
|Date:||21-February-2012 at 01:55||Lines Added:||8|
|Commit Comment:||Fixed bug 1424 - Handling of alpha channel in Altivec accelerated blit functions
evilbite 2012-02-19 09:38:21 PST
There is only one Altivec accelerated blit function
(ConvertAltivec32to32_prefetch() or ConvertAltivec32to32_noprefetch(),
depending on the CPU used) that is supposed to handle all alpha combinations.
This works as follows for every pixel line:
1. Blit single pixels until an aligned address is reached
2. Accelerated blit as far as possible
3. Blit single remaining pixels
Part 2. is set up correctly to handle different combinations of the alpha
channels of the participating surfaces. Parts 1. and 3. only do a simple copy
of all the pixel's components from souce to destination. But when the source
surface has no alpha channel (Amask is 0, e.g. the video surface) the surface's
alpha value must be used instead. Otherwise crap (uninitialized data) is being
copied to the destiniation's alpha channel.
The attached patch is a quick'n'dirty solution to the problem. A more
sophisticated solution might require separate functions for different
combinations of the alpha channels of the participating surfaces.
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