Fixed bug 3309 - SDL_ConvertSurface adds AlphaMod when input surface has ColorKey

Sylvain

Let's you have a SDL_Surface that has ColorKey, but no Alpha Modulation.
When this surface is duplicated with SDL_ConvertSurface function, the result has ColorKey and Alpha Modulation (BLEND, and Opaque 255).

I think SDL_ConvertSurface should strictly keeps the input format.


example
=======

SDL_Surface *input; // ... Set up a surface with ColorKey and no AlphaMod

SDL_Surface *output = SDL_ConvertSurface(input, input->format, input->flags);

// "output" surface has a ColorKey but *also* AlphaMod (BLEND, and Opaque 255).

src/video/SDL_surface.c

@@ -986,7 +986,7 @@ SDL_ConvertSurface(SDL_Surface * surface, const SDL_PixelFormat * format,
     /* Enable alpha blending by default if the new surface has an
      * alpha channel or alpha modulation */
     if ((surface->format->Amask && format->Amask) ||
-        (copy_flags & (SDL_COPY_COLORKEY|SDL_COPY_MODULATE_ALPHA))) {
+        (copy_flags & SDL_COPY_MODULATE_ALPHA)) {
         SDL_SetSurfaceBlendMode(convert, SDL_BLENDMODE_BLEND);
     }
     if ((copy_flags & SDL_COPY_RLE_DESIRED) || (flags & SDL_RLEACCEL)) {