Since I wrote that tutorial, I may as well try to answer your questions :) I have a few cel-shaded images in project. I am stumbling on a major limitation of the cel-shading as explained in the tutorial... so right now, I am pretty much stuck. The cel-shading effect in the tutorial relies on the 'incident angle' to trace the outline of an object. This works reasonably well for smooth, curved objects. It does not work on sharp edges, such as a cube. For that, we would need a parameter such as 'local curvature' or maybe 'local angle between two edges of a polygon'. To answer your second question, the effect in the tutorial works well with ecosystems. The flowers in the final scene with the 'bunny' are generated with an ecosystem.

• agiel - www.linfa.net