Surface Light Cones: Sharing Direct Illumination for Efficient Multi-viewer Rendering

Even though stochastic methods and hardware supported ray tracing are increasingly used for computing direct illumination, the efficient real-time rendering of dynamic area light sources still forms a challenge. In this paper, we propose a method for representing and caching direct illumination information using a compact multi-cone representation that is stored on the surface of objects. While shading due to direct illumination is typically heavily view-dependent, the incoming radiance for surface points is view-independent. Relying on cones, to represent the projection of the dominant visible light sources, allows to reuse the incoming radiance information across frames and even among multiple cameras or viewers within the same scene. Progressively refining and updating the cone structures not only allows to adapt to dynamic scenes, but also leads to reduced noise levels in the output images compared to sampling based methods. Relying on surface light cones allows to render single viewer setups 2-3x faster than random sampling, and 1.5-2x faster than reservoir-based sampling with the same quality. The main selling point for surface light cones is multi-camera rendering, For stereo rendering, our approach essentially halves the time required for determining direct light visibility. For rendering in the cloud, where multiple viewers are positioned close to another, such as in virtual meetings, gathering locations in games, or online events such as virtual concerts, our approach can reduce overall rendering times by a factor of 20x for as few as 16 viewers in a scene compared to traditional light sampling. Finally, under heavily constraint ray budgets where noise levels typically overshadow bias, surface light cones can dramatically reduce noise.