Get the color key (transparent pixel) for a surface.
int SDL_GetColorKey(SDL_Surface * surface, Uint32 * key);
|surface||the SDL_Surface structure to query|
|key||a pointer filled in with the transparent pixel|
Returns 0 on success or a negative error code on failure; call SDL_GetError() for more information.
The color key is a pixel of the format used by the surface, as generated by SDL_MapRGB().
If the surface doesn't have color key enabled this function returns -1.
This function is available since SDL 2.0.0.