Toward practical real-time photon mapping
Proceedings of the ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games - I3D '13
Figure 1 : A warehouse in which small gaps create a complex, indirect paths for late afternoon sunlight from windows on the far right. The Tiled algorithm computes scattered indirect illumination from traced photons for this scene in 28ms at 1920×1080 on the mid-range NVIDIA GeForce 670 GPU. The inset image with only direct illumination shows the importance of rendering indirect light for this scene. Abstract We describe the design space for real-time photon density estimation, the key step of
... endering global illumination (GI) via photon mapping. We then detail and analyze efficient GPU implementations of four best-of-breed algorithms. All produce reasonable results on NVIDIA GeForce 670 at 1920×1080 for complex scenes with multiple-bounce diffuse effects, caustics, and glossy reflection in real-time. Across the designs we conclude that tiled, deferred photon gathering in a compute shader gives the best combination of performance and quality. Keywords: photon map, global illumination, distribution correct result as more computational power is made available and degrades gracefully (by blurring lighting) on lower-end devices. Other fast GI algorithms [e.g., VPLs, Direct-to-Indirect, Irradiance Volumes] do not provide all of these properties simultaneously. A limitation of photon mapping is that does not capture transport paths that terminate in a series of perfectly-specular scattering events (i.e., eye reflections and refractions). Those must be ray traced or approximated with screen space techniques. Why fast? Offline global illumination takes minutes to hours to render with current tools. Bringing this time down by two orders of magnitude, to around 0.2-1.0s, will be transformative for design applications (i.e., CAD and DCC). It will change workflow from render-and-wait to interactive editing of lighting, materials, and geometry. This will enable efficient workflow for architects, industrial designers, film lighting technicians, and game developers creating design spaces and lighting.