VMF Diffuse: A unified rough diffuse BRDF

Abstract

We present a practical analytic BRDF that approximates scattering from a generalized microfacet volume with a von Mises-Fischer NDF. Our BRDF seamlessly blends from smooth Lambertian, through moderately rough height fields with Beckmann-like statistics and into highly rough/porous behaviours that have been lacking from prior models. At maximum roughness, our model reduces to the recent Lambert-sphere BRDF. We validate our model by comparing to simulations of scattering from geometries with randomly-placed Lambertian spheres and show an improvement relative to a rough Beckmann BRDF with very high roughness.