SSRT3: Screen Space Ray Tracing (GI)

Real-time global illumination using screen-space information for HDRP. Like our previous implementations (SSRT) the algorithm is based on GTAO and uses a horizon-based method to retrieve GI samples, which makes it a lot less noisy/blurry than HDRP's SSGI. Performance is also better than SSGI, at around 2-3 ms on an RTX 3060 for the entire effect. Our novel method bypasses the infinite thickness limitation typical of horizon-based methods and enables light to pass behind thin surfaces. More details in the paper (open access preprint here).

Fallback to Adaptive Probe Volumes (APV) or Reflection Probes (static or updated every frame) is used to gather lighting that is not present on the screen. This ensures that the illumination is stable no matter where the camera is looking.

Features:

• Multi-bounce indirect diffuse lighting and occlusion
• Support of emissive surfaces as an indirect light source
• Directional occlusion of ambient light (similar to bent normals, but handles thin surfaces better)
• Fallback to HDRP Ambient Probe Volumes (APV) and Reflection Probes for out-of-screen light

Limitations:

• It only works for HDRP
• It only works in deferred mode

Has been tested on Unity 2021.2 and 2022.1 (with HDRP 12 and 13 respectively). Since it's implemented as a custom post-process it should work on most HDRP versions. There are no additional dependencies apart from HDRP.

For questions or support contact us at [email protected].