“Fast furry ray gathering” by Neulander

  • ©Ivan 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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