fixed bug with copying color key if surfaces have different format

This bug occurs when getting the color key of a surface and setting it
as the color key of another surface that has a surface format that
differs from that of the first surface.

This bug occurs in conjunction with the workaround for the color key
bug in SDL 2.0.12 which prevents transparency in graphics files with
color palette. (See commit 6b6c9eb2 for that workaround.)

Especially, this bug combination occurs on the high score screen of
Alan Bond's "Snake Bite" level set, which then only shows a headline
on a black screen. (This screen uses a trick to show each line on the
screen in a different color by using a background with different
colors and an inverted font with transparent characters and opaque
black surroundings, so missing transparency leads to "black text on
black background".)

diff --git a/src/libgame/sdl.c b/src/libgame/sdl.c
index cbdbdc1cfcac586f1a414bc5e2f3d053a3636d2b..0325c45f038383c8a5e971be60c59dd1d9930906 100644 (file)
--- a/src/libgame/sdl.c
+++ b/src/libgame/sdl.c
@@ -297,6 +297,7 @@ static boolean equalSDLPixelFormat(SDL_PixelFormat *format1,
          format1->Bmask         == format2->Bmask);
 }
 
+#if 0
 static Pixel SDLGetColorKey(SDL_Surface *surface)
 {
   Pixel color_key;
@@ -306,6 +307,31 @@ static Pixel SDLGetColorKey(SDL_Surface *surface)
 
   return color_key;
 }
+#endif
+
+static void SDLCopyColorKey(SDL_Surface *src_surface, SDL_Surface *dst_surface)
+{
+  Pixel color_key;
+  Uint8 r, g, b;
+
+  // check if source surface has a color key
+  if (SDL_GetColorKey(src_surface, &color_key) == 0)
+  {
+    // get RGB values of color key of source surface
+    SDL_GetRGB(color_key, src_surface->format, &r, &g, &b);
+
+    // get color key from RGB values in destination surface format
+    color_key = SDL_MapRGB(dst_surface->format, r, g, b);
+
+    // set color key in destination surface
+    SDL_SetColorKey(dst_surface, SET_TRANSPARENT_PIXEL, color_key);
+  }
+  else
+  {
+    // unset color key in destination surface
+    SDL_SetColorKey(dst_surface, UNSET_TRANSPARENT_PIXEL, 0);
+  }
+}
 
 static boolean SDLHasColorKey(SDL_Surface *surface)
 {
@@ -366,8 +392,7 @@ SDL_Surface *SDLGetNativeSurface(SDL_Surface *surface)
 
   // workaround for a bug in SDL 2.0.12 (which does not convert the color key)
   if (SDLHasColorKey(surface) && !SDLHasColorKey(new_surface))
-    SDL_SetColorKey(new_surface, SET_TRANSPARENT_PIXEL,
-                   SDLGetColorKey(surface));
+    SDLCopyColorKey(surface, new_surface);
 
   return new_surface;
 }
@@ -2269,8 +2294,7 @@ Bitmap *SDLZoomBitmap(Bitmap *src_bitmap, int dst_width, int dst_height)
 
   // set color key for zoomed surface from source surface, if defined
   if (SDLHasColorKey(src_surface))
-    SDL_SetColorKey(dst_surface, SET_TRANSPARENT_PIXEL,
-                   SDLGetColorKey(src_surface));
+    SDLCopyColorKey(src_surface, dst_surface);
 
   // create native non-transparent surface for opaque blitting
   dst_bitmap->surface = SDLGetOpaqueSurface(dst_surface);