A microfacet-based shadowing function to solve the bump terminator problem

Abstract

We present a technique to hide the abrupt shadow terminator line when strong bump or normal maps are used to emulate micro-geometry. Our approach, based on microfacet shadowing functions, is simple and inexpensive. Instead of rendering detailed and expensive height-field shadows, we apply a statistical solution built on the assumption that normals follow a nearly normal random distribution. We also contribute a useful approximate variance measure for GGX, which is otherwise undefined analytically.