R&D: Real-Time Path-Tracing in Unreal Engine 5

We explored the NVIDIA version of Unreal Engine, which incorporates advanced features such as real-time Path Tracing (ReSTIR), DLSS, and more.

Path tracing is one of the most accurate rendering methods, allowing light to be simulated per pixel to achieve exceptional physical realism. However, this technique is extremely resource-intensive, both in terms of computation time and hardware requirements — a single frame can sometimes take several hours or even days to render. That’s why achieving this level of quality in real time represents a major breakthrough in 3D rendering.

According to our research, ReSTIR GI works by tracing the path of a single pixel (or sample) and then approximating neighboring pixels using a spatio-temporal reservoir. All the resulting data is then processed and denoised via DLSS Ray Reconstruction, enabling real-time path tracing.

This ReSTIR GI technique is available on a dedicated Unreal Engine branch developed by NVIDIA. In our tests, there remains a small gap between ReSTIR and full path tracing, but this difference is shrinking rapidly as the technology evolves.

For our tests, we used the Entertainment Pack asset from the Marketplace on an RTX 3080. For reference, the following Unreal Engine 5 CVARs were used:

r.RayTracing.SampledLighting.Denoiser = 1
r.NGX.DLSS.DenoiserMode = 1