Fast environmental lighting for local-PCA encoded BTFs

Rendering geometric models with complex surface materials in arbitrary lighting environments is a challenging problem. In order to relight and render geometries covered with complex, measured BTFs two problems have to be addressed: the memory problem resulting from the large size of the measured BTF data and the light integration problem resulting from summing up the contributions from all measured light-sources. In this paper we describe how highly efficient BTF compression methods like local-PCA and suitable representations of environmental light based on spherical harmonics can be combined leading to fast environmental lighting for efficiently encoded BTFs. As a side effect the method supports precomputed radiance transfer