DDISH-GI : Dynamic Distributed Spherical Harmonics Global Illumination

Abstract

We propose a real-time hybrid rendering algorithm that off-loads computationally complex rendering of indirect lighting from mobile client devices to dedicated ray tracing hardware on the server with a hybrid real-time computer graphics rendering algorithm. Spherical harmonics (SH) light probes are updated with path tracing on the server side, and the final frame is rendered with a fast rasterization-based pipeline that uses the light probes to approximate high quality indirect diffuse lighting and glossy specular reflections. That is, the rendering workload can be split to multiple devices across the network with a small bandwidth usage. It also benefits multi-user and multi-view scenarios by separating indirect lighting computation from camera positioning. Compared to simply streaming fully remotely rendered frames, the approach is more robust to network interruptions and latency. Furthermore, we propose a specular approximation for GGX materials via zonal harmonics (ZH). This alleviates the need to implement more computationally complex algorithms, such as screen space reflections, which was suggested in the state-of-the-art dynamic diffuse global illumination (DDGI) method. We show that the image quality of the proposed method is similar to that of DDGI, with a 23 times more compact data structure.