Textures and radiosity: controlling emission and reflection with texture maps

Abstract

In this paper we discuss the efficient and accurate incorporation of texture maps into a hierarchical Galerkin radiosity algorithm. This extension of the standard algorithm allows the use of textures to describe complex reflectance and emittance patterns over surfaces, increasing the realism and complexity of radiosity images. Previous approaches to the inclusion of textures have either averaged the texture to yield a single color for the radiosity computations, or exhaustively generated detail elements—possibly as many as one per texture pixel. The former does not capture important lighting effects due to textures, while the latter is too expensive computationally to be practical. To handle texture maps requires a detailed analysis of the underlying operator equation. In particular we decompose the radiosity equation into two steps: (i) the computation of irradiance on a surface from the radiosities on other surfaces, and (ii) the application of the reflectance operator &rgr; to compute radiosities from irradiances. We then describe an algorithm that maintains hierarchical representations of both radiosities and textures. The numerical error involved in using these approximations is quantifiable and a time/error tradeoff is possible. The resulting algorithm allows texture maps to be used in radiosity computations with very little overhead.