in SDL 1.3 (revision 5508 from SVN), the method used to calculate the
bits per pixel from a “int format” differ between “SDL_ListModes” (which
always uses the “SDL_BITSPERPIXEL” macro) and “SDL_PixelFormatEnumTo-
Masks” (which uses either “SDL_BITSPERPIXEL” or “SDL_BYTESPERPIXEL * 8”,
depending on the value of “SDL_BYTESPERPIXEL”).

Because the values are later compared in “SDL_ListModes” this may lead
to some valid video modes not being returned. In my case the only mode
returned by “SDL_GetNumDisplayModes” was dismissed and NULL was
returned. (This led to the calling application sticking its head in the
sand.)

The attached patch copies the method used within “SDL_PixelFormatEnumTo-
Masks” to “SDL_ListModes”. This solved the problem for me though I don't
fully understand the method used by “SDL_PixelFormatEnumToMasks”.