there seems to be a bug in the BlitSurface-Routine
of SDL 1.0.8 (which seems fixed in SDL 1.1.3, but
might be interesting as 1.0.8 is marked as “stable”):
When the source and destination surface (SDL_SWSURFACE)
are the same in BlitSurface, the blit messes up when
copying overlapping rectangles when the destination
rectangle is right from or below the source rectangle.
I haven’t looked deeper into the code, but I suppose
that the blit routine always uses “ascending” copying
where “descending” copying would be right in that case –
copying overlapping rectangles where the destination
rectangle is left from or above the source rectangle
are correctly blitted.
Everything’s fine in 1.1.3, but maybe this should also
work right in the stable 1.0.x release.
Holger.Schemel at mediaWays.net ++49 +5241