void make_black ();
void make_transparent ();
void alpha_blend (boost::shared_ptr<const Image> image, Position<int> pos);
void copy (boost::shared_ptr<const Image> image, Position<int> pos);
void make_black ();
void make_transparent ();
void alpha_blend (boost::shared_ptr<const Image> image, Position<int> pos);
void copy (boost::shared_ptr<const Image> image, Position<int> pos);