Matrix row-column sampling for the many-light problem

Abstract

2.2m triangles: 300 rows, 900 columns, 16.9 s 388k triangles: 432 rows, 864 columns, 13.5 s 869k triangles: 100 rows, 200 columns, 3.8 s Figure 1: In the above images, over 1.9 million surface samples are shaded from over 100 thousand point lights in a few seconds. This is achieved by sampling a few hundred rows and columns from the large unknown matrix of surface-light interactions. AbstractRendering complex scenes with indirect illumination, high dynamic range environment lighting, and many direct light sources remains a challenging problem. Prior work has shown that all these effects can be approximated by many point lights. This paper presents a scalable solution to the many-light problem suitable for a GPU implementation. We view the problem as a large matrix of samplelight interactions; the ideal final image is the sum of the matrix columns. We propose an algorithm for approximating this sum by sampling entire rows and columns of the matrix on the GPU using shadow mapping. The key observation is that the inherent structure of the transfer matrix can be revealed by sampling just a small number of rows and columns. Our prototype implementation can compute the light transfer within a few seconds for scenes with indirect and environment illumination, area lights, complex geometry and arbitrary shaders. We believe this approach can be very useful for rapid previewing in applications like cinematic and architectural lighting design.

Making Imperfect Shadow Maps View‐Adaptive: High‐Quality Global Illumination in Large Dynamic Scenes

“…Such an idea was pursued in [DGR*09], but temporal coherence remained a major challenge. The same holds for [HPB07] where light groups are established by sampling light–receiver relationships. Only if the entire sequence is known, temporally coherent results are possible [HVAPB08].…”

Virtual spherical lights for many-light rendering of glossy scenes

“…We use matrix row-column sampling [Hašan et al 2007] to achieve scalability with large numbers of lights. The VSL is implemented simply as a new GPU shader.…”

“…Laine et al [2007] propose incremental instant radiosity for animated sequences, where only a subset of shadow maps is recomputed in each frame. Matrix row-column sampling [Hašan et al 2007] samples a small number of rows and columns from the large matrix of lightsurface connections. Lightcuts [Walter et al 2005;Walter et al 2006] use a hierarchy on the set of lights and/or surface samples to improve the scalability of connection computations.…”

“…Many-light methods [Keller 1997;Walter et al 2005;Laine et al 2007;Hašan et al 2007;Ritschel et al 2008] provide good performance, but are incorrect for two reasons. First, the generated virtual point lights (VPLs) are diffuse-only, so light bouncing off glossy surfaces is ignored.…”

Fast, realistic lighting and material design using nonlinear cut approximation

“…These techniques typically rely on offline renderers to sample visibility and achieve high quality. The matrix row-column sampling algorithm [Hašan et al 2007] exploits the GPU to sample and cluster many lights, improving the speed to a few seconds per frame. In contrast, our method aims at exploiting precomputed visibility to support realtime lighting and material changes.…”