An algorithm for producing half-tone computer graphics presentations with shadows and movable light sources

In the years since the introduction of SKETCHPAD an increasing number of graphics systems for line drawing have been developed. Software packages are now available to do such things as picture definition, rotation and translation of picture data, and production of animated movies and microfilm. Automatic windowing, three-dimensional figures, depth cueing by intensity, and even stereo line drawing are now feasible and in some cases, available in hardware.