Microfacet theory concisely models light transport over rough surfaces. Specular reflection is the result of single mirror reflections on each facet, while exact computation of multiple scattering is either neglected, or modeled using costly importance sampling techniques. Practical but accurate simulation of multiple scattering in microfacet theory thus remains an open challenge. In this work, we revisit the traditional V-groove cavity model and derive an analytical, cost-effective solution for multiple scattering in rough surfaces. Our kaleidoscopic model is made up of both real and virtual Vgrooves, and allows us to calculate higher-order scattering in the microfacets in an analytical fashion. We then extend our model to include nonsymmetric grooves, allowing for additional degrees of freedom on the surface geometry, improving multiple reflections at grazing angles with backward compatibility to traditional normal distribution functions. We validate the accuracy of our model against ground-truth Monte Carlo simulations, and demonstrate its flexibility on anisotropic and textured materials. Our model is analytical, does not introduce significant cost and variance, can be seamless integrated in any rendering engine, preserves reciprocity and energy conservation, and is suitable for bidirectional methods.



@article{Lee2018practical, author = {Lee, Joo Ho and Jarabo, Adrian and Jeong, Daniel S. and Gutierrez, Diego and Kim, Min H.}, title = {Practical Multiple Scattering for Rough Surfaces}, journal = {ACM Transactions on Graphics (SIGGRAPH Asia 2018)}, volume = {37}, number = {6}, year = {2018} }



We want to thank Julio Marco for his help with figures, Ibón Guillén for discussions, and the members of the Graphics and Imaging Lab for proofreading. Min H. Kim acknowledges Korea NRF grants (2016R1A2B2013031, 2013M3A6A6073718) and additional support by KOCCA in MCST of Korea, Cross-Ministry Giga KOREA Project (GK17P0200), Samsung Electronics (SRFC-IT1402-02), and an ICT R&D program of MSIT/IITP of Korea (2017-0-00072, 2016-0-00018). Diego Gutierrez and Adrian Jarabo are funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (CHAMELEON project, grant agreement No 682080), DARPA (project REVEAL), and the Spanish Ministerio de Economía y Competitividad (TIN2016-78753-P).