Created attachment 2089 [details]
add SDL_CreateRGBSurfaceWithFormat[From]()

Currently, SDL_CreateRGBSurface() and SDL_CreateRGBSurfaceFrom() take Uint32 masks for RGBA to "describe" the Pixelformat of the surface.
Internally those value are only used to map to one of the SDL_PIXELFORMAT_* enum values that are used for further processing.

I think it would be both handy and more efficient to be able to specify SDL_PIXELFORMAT_* yourself without using SDL_PixelFormatEnumToMasks() to create masks first, so I implemented functions that do that:
SDL_CreateRGBSurfaceWithFormat() and SDL_CreateRGBSurfaceWithFormatFrom() which are like the versions without "WithFormat" but instead of taking 4 Uint32s for R/G/B/A masks, they take one for a SDL_PIXELFORMAT_* enum value.

Together with https://bugzilla.libsdl.org/show_bug.cgi?id=2923 creating a SDL_Surface* from RGBA data (e.g. from stb_image)  is as easy as
  surf = SDL_SDL_CreateRGBSurfaceWithFormat(0, w, h, bppToUse*8, SDL_PIXELFORMAT_RGBA32);