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Multi-Scale Rendering of Scratched Materials using a Structured SV-BRDF Model

Boris Raymond, Gael Guennebaud, Pascal Barla
ACM Transactions on Graphics (TOG), 2016, , d.o.i. 10.1145/2897824.2925945

We introduce a Spatially-Varying BRDF model tailored to the multi-scale rendering of scratched materials such as metals, plastics or finished woods. Our approach takes advantage of the regular structure of scratch distributions to achieve high performance without compromising visual quality. We provide users with controls over the profile, micro-BRDF, density and orientation of scratches, while updating our material model at interactive rates. The BRDF for a single scratch is simulated using an optimized 2D ray-tracer and compactly stored in a three-component 2D texture. In contrast to existing models, our approach takes into account all inter-reflections inside a scratch, including Fresnel effects. At render time, the SV-BRDF for the scratch distribution under a pixel or ray footprint is obtained by linear combination of individual scratch BRDFs. We show how to evaluate it using both importance and light sampling, in direct and global illumination settings.