[SDL] Per-Surface alpha and SDL_DisplayFormatAlpha

[Jonathan Dearborn]

Hi,
 
When I IMG_Load() a .png I get a per-surface alpha of 255.  This means that the surface is definitely using 255 as fully opaque.  If I blit this surface using SDL_BlitSurface(), it works fine.  Now if I use SDL_DisplayFormatAlpha() on the surface, the per-surface alpha becomes 0.  This apparently means that 0 is fully opaque now.  If I blit it with SDL_BlitSurface(), it still works correctly.  Is there a way that I can use to emulate this functionality of SDL_BlitSurface()?  What can I use to determine if a surface uses 0 or 255 as fully opaque?
 
Jonny D
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