Real-time hatching

Real-time hatching
Emil Praun, Hugues Hoppe, Matthew Webb, Adam Finkelstein.
ACM SIGGRAPH 2001 Proceedings, 581-586.
Fast nonphotorealistic rendering using precomputed tonal art maps.
Abstract: Drawing surfaces using hatching strokes simultaneously conveys material, tone, and form. We present a real-time system for non-photorealistic rendering of hatching strokes over arbitrary surfaces. During an automatic preprocess, we construct a sequence of mip-mapped hatch images corresponding to different tones, collectively called a tonal art map. Strokes within the hatch images are scaled to attain appropriate stroke size and density at all resolutions, and are organized to maintain coherence across scales and tones. At runtime, hardware multitexturing blends the hatch images over the rendered faces to locally vary tone while maintaining both spatial and temporal coherence. To render strokes over arbitrary surfaces, we build a lapped texture parametrization where the overlapping patches align to a curvature-based direction field. We demonstrate hatching strokes over complex surfaces in a variety of styles.
Hindsights: Hatching and other non-photorealistic effects have become popular in a number of computer games. Our NPAR 2002 paper shows how blending is made simpler using volume textures, and describes a per-pixel thresholding scheme for more realistic pen strokes.