Light Sampling in Quake 2 Using Subset Importance Sampling

Abstract

In the context of path tracing, to compute high-quality lighting fast, good stochastic light sampling is just as important as light culling is in the context of raster graphics. In order to enable path tracing in Quake 2, multiple solutions were evaluated. Here, we describe the light sampling solution that ended up in the public release. We also discuss its relation to more recent approaches like ReSTIR [4], real-time path guiding [11], and stochastic lightcuts [19]. Finally, we leverage the power of variance reduction techniques known from offline rendering, by providing an extension of our stochastic light sampling technique that allows use of multiple importance sampling (MIS). The resulting algorithm can be seen as a variant of stochastic MIS, which was recently proposed in the framework of continuous MIS [34]. To this end, we derive additional theory to introduce pseudo-marginal MIS, allowing for effective variance reduction by marginalization with respect to only parts of the sampling process.