NVIDIA has announced an update to the NvRTX branch of Epic's Unreal Engine 5. The major new feature is the addition of experimental support for ReSTIR Global Illumination, the ray tracing algorithm first discussed by NVIDIA researchers in the seminal paper Spatiotemporal Reservoir Resampling for Real-Time Ray Tracing with Dynamic Direct Lighting released at ACM SIGGRAPH 2020.
ReSTIR GI allows 'direct lighting from millions of moving lights' with ray budgets that are compatible with the demands of real-time rendering for games. The approach also doesn't require complex light structure, baking, or global scene parameterization, while still providing results up to 65x faster than prior techniques. All of the lights cast shadows, everything can move however necessary, and new emitters can be added dynamically.
Since then, ReSTIR GI has been implemented in just two games: DESORDRE: A Puzzle Game Adventure and CD Projekt RED's Cyberpunk 2077 with Patch 2.1, which dropped last December. Modder Pascal Gilcher (also known as Marty McFly) showcased a work-in-progress path tracing ReShade mod featuring lighting based on the ReSTIR GI technique, though the mod is still far from done. Meanwhile, fellow modder NiceGuy also implemented a technique inspired by ReSTIR GI in his Complete RT shader (version 1.3).
The impact of this official addition is, of course, on another level entirely. Unreal Engine 5 is by far the most popular engine among PC and console developers and, as such, the potential adoption is immeasurably greater.
The implementation on the NvRTX branch was handled by NVIDIA's Jiayin Cao, who first joined NVIDIA in 2012 as a Developer Technology Engineer based in Shanghai, China. In 2016, he moved to Singapore to work at Ubisoft on Skull and Bones (which finally launched earlier this year after a very long development), where he filled the role of Senior Graphics Engineer. In August 2019, he moved to the United States to work on The Last of Us Part II as a Graphics Engineer at Naughty Dog. A couple of years later, he moved to Ready at Dawn as a Senior Graphics Engineer on the Oculus VR exclusive game Lone Echo II. He returned to NVIDIA (while staying in the United States) in early 2023, focusing on NvRTX. On Twitter/X, he wrote:
We are making a lot of improvements in UE's rendering pipeline by taking advantage of RTX hardware. It happens on UE NvRTX branch. Here is the latest ReSTIR GI implementation that we've done in Unreal Engine 5, which lights the scene with only emissive materials.
Our GDC update for the nvrtx branch of UE5 is out. Some great work by @Jiayin_Cao in shipping an experimental implementation or ReSTIR GI. Attached video is only lit via emissive surfaces w/ ReSTIR GI. pic.twitter.com/Re75rWdaF3
— Evan Hart (@PixelCurmudgeon) May 1, 2024
Cao then answered a few questions on the popular social media channel. When asked how ReSTIR GI runs in Unreal Engine 5, he said it had some 'limitations' that NVIDIA is trying to improve. The best way to check is simply to access the NvRTX branch and run it on your PC. As a reminder, here's what you need to access that version of UE5:
- Create a GitHub account - Navigate to GitHub and sign up for an account
- Open your Unreal Engine account dashboard
- Connect GitHub
- Link the accounts
- Authorize through the OAuth App Authorization Process
- Accept the email invitation
Moreover, he confirmed there's an option to allow ReSTIR GI to work in tandem with UE5's Lumen. Unreal Engine 5 already supports RTX Direct Illumination, which is also based on a ReSTIR implementation, giving game developers plenty of ray tracing and path tracing options.
To that end, NVIDIA has already scheduled a webinar titled Path Traced Visuals in Unreal Engine. Hosts Richard Cowgill and Zach Lo will discuss what ReSTIR means for the future of real-time lighting, show lighting workflow examples in a demo, and learn how to access the technology through the NvRTX UE5 branch.
