[SDL] BUG[?]: 32bpp RGBA->RGB colorkey blit, no SDL_SRCALPHA

Alex Volkov avcp-sdlmail at usa.net
Thu Nov 10 18:53:40 PST 2005


It seems there is either a documentation vs. reality mismatch or a real bug
in SDL_blit_N.c:BlitNtoNKey().
The exact blit in question is a 32bpp RGBA->RGB, where RGBA has SDL_COLORKEY
and *no* SDL_SRCALPHA flags. The doc in SDL_video.h states:
* RGBA->RGB:
*     SDL_SRCALPHA not set:
* 	copy RGB.
* 	if SDL_SRCCOLORKEY set, only copy the pixels matching the
* 	RGB values of the source colour key, ignoring alpha in the
* 	comparison. 

BlitNtoNKey(), however, forgets to "ignore alpha in the comparison". The
documentation makes perfect sense, so I think it is the code that is faulty.

The attached patch corrects the code.

-Alex.
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