/*  call-seq:
 *     flip()
 *
 *  If the Rubygame display is double-buffered (see Screen.new), flips
 *  the buffers and updates the whole screen. Otherwise, just updates the
 *  whole screen.
 */
VALUE rbgm_screen_flip(VALUE self)
{
  SDL_Surface *screen;
  Data_Get_Struct(self, SDL_Surface, screen);
  SDL_Flip(screen);
  return self;
}