/* 
 *  call-seq:
 *     alpha
 *
 *  Return the per-surface alpha (opacity; non-transparency) of the surface.
 *  It can range from 0 (full transparent) to 255 (full opaque).
 */
VALUE rbgm_surface_get_alpha(VALUE self)
{
        SDL_Surface *surf;
        Data_Get_Struct(self, SDL_Surface, surf);
        return INT2NUM(surf->format->alpha);
}