define mat_mult,
       build_world_to_screen,
       find_eye,
       transform_pt,
       build_screen_pts,
       find_pln_eqn,
       order_pts,
       up,
       dn,
       build_screen_triangles,
       aalias_weight,
       dither_weight,
       aalias_and_dither,
       dither,
       find_dir,
       compute_color
