It really depends on what style you want to achieve but it can get quite hairy pretty fast. Non-photorealistic rendering is actually a whole (fascinating) acad

It really depends on what style you want to achieve but it can get quite hairy pretty fast. Non-photorealistic rendering is actually a whole (fascinating) academic field in itself. Since you have conflicting goals (temporal coherence, spatial coherence, "flatness", relatively constant stroke/feature size, ...) it's full of interesting tradeoffs and techniques. Even simple things like beautiful real-time stylized outlining can be really hard if you are picky about the result.