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.