Talk by Tomasz Stachowiak at SIGGRAPH 2015 in the Advances in Real-time Rendering course.
We present an algorithm for efficiently calculating glossy screenspace reflections in real-time. Our technique robustly handles spatially-varying material properties, such as roughness and normals. It faithfully reproduces specular elongation of microfacet BRDFs, and seamlessly blends with other physically-based rendering techniques. To accomplish this, we use Monte Carlo importance sampling, and reduce the resultant noise using specialized spatial and temporal filtering methods. In order to reduce the number of rays needed, we ray-trace at half-resolution, and reuse the rays shot from adjacent pixels in Monte Carlo integration. We can resolve to full resolution using several rays per pixel, but pay a small fraction of the ray-tracing.