All-frequency relighting of glossy objects

Rui Wang, John Tran, David Luebke
2006 ACM Transactions on Graphics  
We present a technique for interactive rendering of glossy objects in complex and dynamic lighting environments that captures interreflections and all-frequency shadows. Our system is based on precomputed radiance transfer and separable BRDF approximation. We factor glossy BRDFs using a separable decomposition and keep only a few low-order approximation terms, each consisting of a purely view-dependent and a purely light-dependent component. In the precomputation step, for every vertex we
more » ... its visibility and compute a direct illumination transport vector corresponding to each BRDF term. We use modern graphics hardware to accelerate this step, and further compress the data using a non-linear wavelet approximation. The direct illumination pass is followed by one or more interreflection passes, each of which gathers compressed transport vectors from the previous pass to produce global illumination transport vectors. To render at run time, we dynamically sample the lighting to produce a light vector, also represented in a wavelet basis. We compute the inner product of the light vector with the precomputed transport vectors, and the results are further combined with the BRDF view-dependent components to produce vertex colors. We describe acceleration of the rendering algorithm using programmable graphics hardware, and discuss the limitations and tradeoffs imposed by the hardware. Recently Liu et al. [2004] and we [Wang et al. 2004] independently proposed a new formulation that combines separable BRDF approximation [Kautz and McCool 1999] with the wavelet-based PRT for interactive relighting of glossy objects. We apply a separable decomposition to approximate glossy BRDFs with a few low-order terms, each consisting of a purely light-dependent and a purely view-dependent component. The key idea is that the light-dependent components are baked into precomputation as part of the transport function definition, and the view-dependent components are accessed during rendering to produce view-dependent effects. However, both papers are limited to direct illumination, ignoring interreflections. In this article we show through derivation that interreflections can be efficiently simulated in the same framework without sacrificing rendering performance. The only additional cost is at precomputation, where the direct illumination pass is followed by one or more interreflection passes. Each interreflection pass gathers transport vectors from the previous pass, producing a new set of vectors carrying bounced illumination. The additional computation simulates both diffuse and glossy interreflections at the same time, and does not increase precomputed data size, allowing us to portray interreflections at the same rendering speed. In general, any precomputation technique is a form of sampling in the 6D space of light direction, view direction and surface location, which must be densely sampled in order to resolve high-frequency illumination effects. For example, high-frequency
doi:10.1145/1138450.1138456 fatcat:f3z65guzf5f2nc4brrvsqfate4