SDL_ConvertSurface (3) - Linux Manuals
SDL_ConvertSurface: Converts a surface to the same format as another surface.
NAMESDL_ConvertSurface - Converts a surface to the same format as another surface.
Creates a new surface of the specified format, and then copies and maps the given surface to it. If this function fails, it returns NULL.
The flags parameter is passed to SDL_CreateRGBSurface and has those semantics.
This function is used internally by SDL_DisplayFormat.
SDL_CreateRGBSurface, SDL_DisplayFormat, SDL_PixelFormat, SDL_Surface