Depicting shape features with directional strokes and spotlighting

This work presents a new algorithm and technique for rendering triangular surfaces in pen-and-ink edge-based strokes. Our technique integrates two very important illustration strategies for depicting shape features: selection of drawing direction and the use of light. Drawing direction is given by four stroke directional fields. For lighting, we introduce the idea of "spotlight silhouettes" for fast illumination computation, with target tone matched by adaptive stroke length adjustment. Stroke style is achieved by path perturbation and noise-based weight control. Our technique also allows visual effects of reverse tone values and depth cueing. Examples with models from anatomy and archeology demonstrate the capabilities of our system.