+ int transparent = 0;
+ int opaque = 0;
+ int semitransparent = 0;
+ int alphasum = 0;
+ int squaredalphasum = 0;
+ bool colors[(1 << 12)];
+ memset(colors, 0, (1 << 12) * sizeof(bool));
+
+ int bpp = src->format->BytesPerPixel;
+ if(SDL_MUSTLOCK(src))
+ {
+ SDL_LockSurface(src);
+ }
+ for(int y = 0;y < src->h;y++) {
+ for(int x = 0;x < src->w;x++) {
+ Uint8 *pixel = (Uint8 *) src->pixels + y * src->pitch + x * bpp;
+ Uint32 mapped = 0;
+ switch(bpp) {
+ case 1:
+ mapped = *pixel;
+ break;
+ case 2:
+ mapped = *(Uint16 *)pixel;
+ break;
+ case 3:
+#if SDL_BYTEORDER == SDL_BIG_ENDIAN
+ mapped |= pixel[0] << 16;
+ mapped |= pixel[1] << 8;
+ mapped |= pixel[2] << 0;
+#else
+ mapped |= pixel[0] << 0;
+ mapped |= pixel[1] << 8;
+ mapped |= pixel[2] << 16;
+#endif
+ break;
+ case 4:
+ mapped = *(Uint32 *)pixel;
+ break;
+ }
+ Uint8 red, green, blue, alpha;
+ SDL_GetRGBA(mapped, src->format, &red, &green, &blue, &alpha);
+ if(alpha < 16)
+ {
+ transparent++;
+ }
+ else if (alpha > 240)
+ {
+ opaque++;
+ alphasum += alpha;
+ squaredalphasum += alpha * alpha;
+ }
+ else
+ {
+ semitransparent++;
+ squaredalphasum += alpha * alpha;
+ }
+ if(alpha != 0)
+ {
+ colors[((red & 0xf0) << 4) | (green & 0xf0) | ((blue & 0xf0) >> 4)] = true;
+ }
+ }
+ }
+ if(SDL_MUSTLOCK(src))
+ {
+ SDL_UnlockSurface(src);
+ }
+ int avgalpha = (opaque + semitransparent) ? alphasum / (opaque + semitransparent) : 0;
+ int avgsquaredalpha = (opaque + semitransparent) ? squaredalphasum / (opaque + semitransparent) : 0;
+ int alphavariance = avgsquaredalpha - avgalpha * avgalpha;
+ if(semitransparent > ((transparent + opaque + semitransparent) / 8) && alphavariance > 16)
+ {
+ return SDL_DisplayFormatAlpha(src);
+ }
+ int keycolor = -1;
+ for(int i = 0;i < (1 << 12);i++)
+ {
+ if(!colors[i])
+ {
+ keycolor = i;
+ }
+ }
+ if(keycolor == -1)
+ {
+ return SDL_DisplayFormatAlpha(src);
+ }
+ SDL_Surface *dst = SDL_CreateRGBSurface(src->flags & ~(SDL_SRCALPHA), src->w, src->h, src->format->BitsPerPixel, src->format->Rmask, src->format->Gmask, src->format->Bmask, 0);
+ bpp = dst->format->BytesPerPixel;
+ Uint32 key = SDL_MapRGB(dst->format, (((keycolor & 0xf00) >> 4) | 0xf), ((keycolor & 0xf0) | 0xf), (((keycolor & 0xf) << 4) | 0xf));
+ 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 red, green, blue, alpha;
+ SDL_GetRGBA(mapped, src->format, &red, &green, &blue, &alpha);
+ if(alpha < (avgalpha / 4))
+ {
+ mapped = key;
+ }
+ else
+ {
+ mapped = SDL_MapRGB(dst->format, red, green, blue);
+ }
+ 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);
+ }
+ if(avgalpha < 240)
+ {
+ SDL_SetAlpha(dst, SDL_SRCALPHA | SDL_RLEACCEL, avgalpha);
+ }
+ SDL_SetColorKey(dst, SDL_SRCCOLORKEY | SDL_RLEACCEL, key);
+ SDL_Surface *convert = SDL_DisplayFormat(dst);
+ SDL_FreeSurface(dst);
+ return convert;