X-Toon: The Extended Toon Shader

The X-Toon shader is a cartoon shading technique created by two French researchers at Artis in collaboration with Lee Marosian. X-Toon extends traditional cartoon shading one-dimensional texture mapping by using a two-dimensional texture map instead. This allows the artist to create depth, lighting, and viewpoint effects instead of being constrained to only lighting effects.

Traditional cartoon shading using a one-dimensional texture map is indexed with dot(norm, lightDir) where norm is the surface normal of the object being rendered at the current point and lightDir is the direction of the light from this point.

X-Toon extends this one-dimensional texture look up into two dimensions by using not only the previous dot product as an index but also a second parameter. The second parameter can be anything required to achieve the desired effect. In the paper they describe both an orientation based look up (based on the dot product between the normal and the view vectors) and a depth based look up. See their paper and website for details and results of the implementation.

The following is a video of the orientation and depth based effects created by the X-Toon shader. I created this application as a mini-project in a course at school using that same textures the original authors use. The first effect simulates varying opacity while the second simulates varying lighting based on orientation and view. The red texture on the car simulates backlighting, an effect normally faked by rendering a scene twice, rendered with one pass using the X-Toon texture mapping. The rest of the video shows depth-based effects and focuses on level of abstraction at far distances.


The best thing about this technique is that it's fast, simple, and new effects can easily be created by any artist. It's also an effective way to blend two different styles of rendering, which is an area of NPR I am currently looking into.