Wraps SDL_GetSurfaceBlendMode which gets the dsdl2.Surface's dsdl2.BlendMode defining blitting
dsdl2.BlendMode of the dsdl2.Surface
dsdl2.SDLException if dsdl2.BlendMode unable to get
See Implementation
Wraps SDL_GetSurfaceBlendMode which gets the dsdl2.Surface's dsdl2.BlendMode defining blitting