Toon shading

Left: with toon shader
Right: Painted textures







I modified a version of a cel/toon shader from the "Advanced Renderman" book by stripping away the fill-color functions and replacing them with an opacity and color texture map read function.  I had to add some texture manipulation functionality since my maps kept appearing upside down.  The outline function was largely left the same, with some slight modifications to thickness.

The results are interesting.  I'm not sure if I like the outline effect as it seems a bit distracting to the eye.  Below you can see two test renders.
On the left is the toon outline shader over a texture that has outlines manually painted on the map.  On the right is just the fill color with the toon outline shader applied.