added workaround for a bug in SDL 2.0.12 which prevents transparency

Unfortunately, the current stable release version 2.0.12 of the SDL
library used by R'n'D has a critical bug that causes all transparent
images in R'n'D to be opaque, which hurts the game graphics at various
places.

The cause of this bug is in SDL_ConvertSurface(), which does not copy
the color key anymore.

The bug is documented in the SDL bug tracking system as follows:
https://bugzilla.libsdl.org/show_bug.cgi?id=2979

The bug will be fixed in the next stable release of the SDL library.

This workaround checks if a converted surface should have a color key,
and explicitly sets it if it is missing in the newly created surface.

diff --git a/src/libgame/sdl.c b/src/libgame/sdl.c
index 7fb650f1b17e9d6070db72855db59cf9c5e34c61..457f567ad59f461b3b90266785d9ec014bfa969d 100644 (file)
--- a/src/libgame/sdl.c
+++ b/src/libgame/sdl.c
@@ -353,6 +353,11 @@ SDL_Surface *SDLGetNativeSurface(SDL_Surface *surface)
   if (new_surface == NULL)
     Error(ERR_EXIT, "SDL_ConvertSurface() failed: %s", SDL_GetError());
 
+  // 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));
+
   return new_surface;
 }