Interactive pen-and-ink rendering for implicit surfaces

and implicit function. We have also experimented with sugges- tive contours (radial curvature kr = 0), using a finite-difference ap- proach which does not require third derivatives. Mesh resolution appears to have more effect on suggestive contours, although we have not carefully tuned the various available parameters. Hidden-line removal presents a challenge, as implicit surface ray- intersection is too slow. The coarse mesh can be used, however feature lines will be erroneously clipped in areas of negative curva- ture. Instead, we again utilize the base mesh. Points are distributed on each triangle and projected to the surface. A small tangent disc is rendered into the z-buffer at each point, providing fast and rea- sonably accurate hidden-line removal. In addition, these discs can