video: Add a fallback case for creating 16-bit surfaces with bogus ma…

…sks.

Fixes #257.

src/SDL12_compat.c

@@ -5003,12 +5003,19 @@ SDL_CreateRGBSurface(Uint32 flags12, int width, int height, int depth, Uint32 Rm
        a generic blitter that just copied data blindly. SDL2 wants more strict
        pixel formats, so try to detect this case and try again with a standard
        format. */
-    if ((surface20 == NULL) && (depth >= 24) && (SDL20_MasksToPixelFormatEnum(depth, Rmask, Gmask, Bmask, Amask) == SDL_PIXELFORMAT_UNKNOWN)) {
+    if ((surface20 == NULL) && (depth >= 16) && (SDL20_MasksToPixelFormatEnum(depth, Rmask, Gmask, Bmask, Amask) == SDL_PIXELFORMAT_UNKNOWN)) {
         /* I have no illusions this is correct, it just works for the known problem cases so far. */
-        Rmask = SDL_SwapLE32(0x000000FF);
-        Gmask = SDL_SwapLE32(0x0000FF00);
-        Bmask = SDL_SwapLE32(0x00FF0000);
-        Amask = SDL_SwapLE32(Amask ? 0xFF000000 : 0x00000000);
+        if (depth == 16) {
+            Rmask = SDL_SwapLE32(0x0000F800);
+            Gmask = SDL_SwapLE32(0x000007E0);
+            Bmask = SDL_SwapLE32(0x0000001F);
+            Amask = 0;
+        } else {
+            Rmask = SDL_SwapLE32(0x000000FF);
+            Gmask = SDL_SwapLE32(0x0000FF00);
+            Bmask = SDL_SwapLE32(0x00FF0000);
+            Amask = SDL_SwapLE32(Amask ? 0xFF000000 : 0x00000000);
+        }
         surface20 = SDL20_CreateRGBSurface(0, width, height, depth, Rmask, Gmask, Bmask, Amask);
     }