nvrtx-May2024 — Joe Raasch

NVRTX Tests

I tried to set up a few different tests using the Nvidia build of Unreal Engine 5.3 (which will be referred to as nvRTX).

The main advantage of nvRTX is RTXDI. This allows for hundreds of dynamic lights to be in a scene with little affect to frame times. There’s an initial performance cost, but adding lights after this is essentially free.

It can do this with algorithms called ReSTIR (Reservoir Spatial/Temporal Importance Sampling)

A very recent addition (added in late April ‘24) is a Global Illumination addition that piggy-backs off of the ReSTIR calculations, called ReSTIR GI. This can also be used for Reflections.

There is deep integration with Unreal. At first, they released ReSTIR integration with Lumen for GI and Reflections, but with the April update it seems that they’re expanding their own solution for this.

One thing to keep in mind is that ReSTIR GI and Reflections feel very ‘beta’. ReSTIR DI feels very solid. The Direct Illumination should be very close to the Pathtracer’s illumination and shadows.

Open nvrtx-May2024 — demonstration 1 in a new tab

Rendered with nvRTX

Open nvrtx-May2024 — demonstration 2 in a new tab

Rendered with the Pathtracer

Try to ignore the weirdness of the hair in the pathtraced version (also it wouldn’t render the debris scattered on the floor).

The arms have more accurate reflections in the pathtraced version.

Notice the heavy denoise in the nvRTX version and how it can remove some detail.

Render Time in Minutes: nvRTX 5; Pathtracer 80

Render Time
Renderer	Minutes
nvRTX	5
Pathtracer	80

For this shot I tried to come up with something that would be difficult for any renderer.

This image is lit with a single emissive object. Emissive objects are always noisey, I wanted to see how nvRTX would handle it, especially as it got darker.

Open nvrtx-May2024 — demonstration 3 in a new tab

This is the nvRTX render. The scene is a single emissive mesh. If you full-screen the clip you’ll get a better idea of the amount of noise. Honestly, I was impressed it was able to handle it as good as it did.

Open nvrtx-May2024 — demonstration 4 in a new tab

This is the Pathtraced version. It has the same lighting setup as the above clip (one emissive mesh).

Notice the GI is brighter in this version. Reflections seemed pretty close between the two versions.

No idea why the debris doesn’t show up on this version.

Open nvrtx-May2024 — demonstration 5 in a new tab

I wanted to see how nvRTX would do with a light instead of the emissive mesh. Much cleaner and faster render time.

Render Time in Minutes: nvRTX Light 4; nvRTX Emissive 17; Pathtracer 148

Render Time
Renderer	Minutes
nvRTX Light	4
nvRTX Emissive	17
Pathtracer	148

One area that nvRTX currently struggles with is mirror-like reflections. There can be a lot of flickering. There might be a CVAR that cleans it up but if there is, I didn’t find it.

Open nvrtx-May2024 — demonstration 6 in a new tab

Notice the crazy flickering on the helmet. This is a known issue with nvRTX that is being worked on. Adding a small amount of roughness can usually clear this up.

Open nvrtx-May2024 — demonstration 7 in a new tab

Check the flickering on the right near the fence area. I tried a bunch of CVars but could not get rid of it.

Of course I could have used Lumen GI and Lumen reflections, but I wanted to test as much new stuff as possible.

This last shot was my favorite. I was really surprised at how closely it matched the Pathtraced version. Really the biggest difference is the flickering in the helmet and some of the background shadowing.

Open nvrtx-May2024 — demonstration 8 in a new tab

This is the nvRTX version. You can notice some GI flickering and the mirror reflections on the helmet has a lot of flickering.

Open nvrtx-May2024 — demonstration 9 in a new tab

The Pathtraced version (2048 samples, 128 Spatial and 16 Temporal)

Render Time in Minutes: nvRTX 30; Pathtracer 197

Render Time
Renderer	Minutes
nvRTX	30
Pathtracer	197