X-Toon: An Extended Toon Shader
Author(s): Pascal Barla, Joëlle Thollot, Lee Markosian.
Proceedings: NPAR '06: Proceedings of the 4th international symposium on Non-photorealistic animation and rendering, pp. 127--132, New York, NY, USA, June, ACM Press,
2006.
[BibTeX] [DOI] 
Abstract:
Traditional toon shading uses a 1D texture that describes how tone varies with surface orientation relative to a given light source. In this paper we describe two extensions to the basic algorithm that support view-dependent effects. First, we replace the 1D texture with a 2D texture whose second dimension corresponds to the desired ``tone detail'', which can vary with depth or surface orientation. This supports effects such as levels-of-detail, aerial perspective, depth-of-field, backlighting, and specular highlights. Second, to control the amount of surface detail depicted by the shader, we further extend the toon shader to use a modified normal field that can range from the original normals to a simpler set of normals taken from an ``abstracted shape.'' A global shape detail parameter determines the degree of interpolation used between the original and abstracted normal fields. We explain how to implement these ideas efficiently on the GPU via vertex and fragment shaders, and discuss ways to extend our approach to alternative tone and shape detail maps.