[SDL] Alpha blending bug in SDL 1.2.11 not present in 1.2.9

[Gabriel Gambetta]

I've run into a strange alpha blending bug in SDL 1.2.11 in Linux. I
used LD_LIBRARY_PATH to load a local copy of 1.2.9 and the bug goes
away. I haven't tested 1.2.10 yet.

The bug involves blitting a RGBA surface over another RGBA surface. I
get transparent pixels that shouldn't be there (see attached image). I'm
not sure about which conditions trigger the bug, but I have a feeling it
has something to do with precision or rounding since storing the alpha
channel as a PNG removes the bug, and when storing the alpha channel in
a JPEG the problem becomes worse as I lower the quality of the JPEG.
However the images *are* loaded correctly, as just rendering the surface
as opposed to blitting it over another one gives the correct result.

Before I dig into the code, is this fixed in CVS or has anyone seen
this?

I'm on Fedora Core 6 in an Atlhon64 3500+.

Thanks,
	--Gabriel


________________________________________________________________________
Gabriel Gambetta
Mystery Studio - http://www.mysterystudio.com
Gabriel on Graphics - http://gabrielongraphics.blogspot.com
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