+namespace
+{
+ SDL_Surface *apply_alpha(SDL_Surface *src, float alpha_factor)
+ {
+ // FIXME: This is really slow
+ assert(src->format->Amask);
+ int alpha = (int) (alpha_factor * 256);
+ SDL_Surface *dst = SDL_CreateRGBSurface(src->flags, src->w, src->h, src->format->BitsPerPixel, src->format->Rmask, src->format->Gmask, src->format->Bmask, src->format->Amask);
+ int bpp = dst->format->BytesPerPixel;
+ if(SDL_MUSTLOCK(src))
+ {
+ SDL_LockSurface(src);
+ }
+ if(SDL_MUSTLOCK(dst))
+ {
+ SDL_LockSurface(dst);
+ }
+ for(int y = 0;y < dst->h;y++) {
+ for(int x = 0;x < dst->w;x++) {
+ Uint8 *srcpixel = (Uint8 *) src->pixels + y * src->pitch + x * bpp;
+ Uint8 *dstpixel = (Uint8 *) dst->pixels + y * dst->pitch + x * bpp;
+ Uint32 mapped = 0;
+ switch(bpp) {
+ case 1:
+ mapped = *srcpixel;
+ break;
+ case 2:
+ mapped = *(Uint16 *)srcpixel;
+ break;
+ case 3:
+#if SDL_BYTEORDER == SDL_BIG_ENDIAN
+ mapped |= srcpixel[0] << 16;
+ mapped |= srcpixel[1] << 8;
+ mapped |= srcpixel[2] << 0;
+#else
+ mapped |= srcpixel[0] << 0;
+ mapped |= srcpixel[1] << 8;
+ mapped |= srcpixel[2] << 16;
+#endif
+ break;
+ case 4:
+ mapped = *(Uint32 *)srcpixel;
+ break;
+ }
+ Uint8 r, g, b, a;
+ SDL_GetRGBA(mapped, src->format, &r, &g, &b, &a);
+ mapped = SDL_MapRGBA(dst->format, r, g, b, (a * alpha) >> 8);
+ switch(bpp) {
+ case 1:
+ *dstpixel = mapped;
+ break;
+ case 2:
+ *(Uint16 *)dstpixel = mapped;
+ break;
+ case 3:
+#if SDL_BYTEORDER == SDL_BIG_ENDIAN
+ dstpixel[0] = (mapped >> 16) & 0xff;
+ dstpixel[1] = (mapped >> 8) & 0xff;
+ dstpixel[2] = (mapped >> 0) & 0xff;
+#else
+ dstpixel[0] = (mapped >> 0) & 0xff;
+ dstpixel[1] = (mapped >> 8) & 0xff;
+ dstpixel[2] = (mapped >> 16) & 0xff;
+#endif
+ break;
+ case 4:
+ *(Uint32 *)dstpixel = mapped;
+ break;
+ }
+ }
+ }
+ if(SDL_MUSTLOCK(dst))
+ {
+ SDL_UnlockSurface(dst);
+ }
+ if(SDL_MUSTLOCK(src))
+ {
+ SDL_UnlockSurface(src);
+ }
+ return dst;
+ }
+}
+