Efficient rendering of outline characters

Resolution-independent windowing systems and raster image processors require efficient and precise rendering of outline characters. Rendering of typographic outline characters involves outline grid fitting, outline scan conversion, and filling. For the purpose of character-outline scan conversion, a highly accurate Bezier spline subdivision stopping criteria is introduced. Recursive Bezier spline subdivision is optimized by maintaining a dedicated Bezier control polygon stack. Scan conversion of contour parts generates in raster memory starting pixels for interior and exterior horizontal spans. Interior horizontal spans are filled very quickly by table accesses. Thanks to the improved recursive subdivision algorithm, character-outline scan conversion speed is increased three-fold. The new subdivision stopping criterion ensures that the produced raster characters are perfectly correct. Respective processing times for grid fitting, outline scan conversion, and filling are given as a function of character size.