“Fast furry ray gathering” by Neulander




    Fast furry ray gathering



    We present several techniques for efficiently gathering diffuse and specular reflection rays originating from hair, recently put in production at Rhythm & Hues. We refine the hair BRDFs from [Neulander 2004] into a new cone-shell model that is more generally applicable and realistic, yet remains simple and fast to evaluate. Next, we address the chief shortcoming of [Neulander 2004]’s hair occlusion model by coupling it with rigorous occlusion-testing of skin geometry. Finally, we deploy a per-strand shading cache to improve performance, adopting a filtering technique in the spirit of trilinear mip-mapping.


    1. Kajiya, J. T., and Kay, T. L. 1989. Rendering fur with three dimensional textures. SIGGRAPH Comput. Graph. 23, 3, 271–280.
    2. Neulander, I. 2004. Quick image-based lighting of hair. In SIGGRAPH 2004 Sketches, 43.

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