Friday, April 16th, 2021 Posted by Jim Thacker

Check out Nvidia’s RTXDI and RTXGI GPU ray tracing demos

Nvidia has released demos showcasing its new GPU ray tracing SDKs, including real-time direct illumination system RTXDI and indirect illumination system RTXGI, at its GTC 2021 technology conference.

The RTX Boulevard demo (above) is a pre-rendered video showing RTXDI (RTX Direct Illumination), which Nvidia describes as making it possible to use millions of area lights in a real-time scene.

The Attic demo is a downloadable executable built on Unreal Engine 4.26 showcasing several Nvidia technologies, including RTXGI (RTX Global Illumination), NRD (Nvidia Realtime Denoisers) and DLSS.

The RTX Boulevard demo: thousands of dynamic, shadow-casting area lights rendered using RTXDI
Announced at GTC last year, RTXDI is described as enabling artists to “render scenes with millions of dynamic area lights in real time” without the need to bake lighting.

The RTX Boulevard demo, recorded running on a top-of-the-range GeForce RTX 3090 gaming GPU, isn’t actually quite that ambitious: it features only “thousands” of lights.

However, they are pretty varied, with geometry including neon billboards, brake lights, apartment windows and even wet roads acting as independent, dynamic, shadow-casting and reflection-generating light sources.

In its simplest implementation, Nvidia descibes RTXDI as a straight replacement for a game engine or real-time renderer’s existing direct lighting system.

Rather than an artist having to select a small number of hero lights for a scene, it removes “all costs associated with culling and identifying important lights, shadow mapping, and ambient occlusion”.

The system is based on a new deep learning algorithm, ReSTIR (Reservoir-based Spatio-Temporal Importance Resampling). You can read a more detailed dive into the technology on Nvidia’s developer blog.

As well as DirectX Raytracing (DXR), the RTXDI SDK supports the new ray tracing extensions for the Vulkan API, making it one of the first new technologies capable of making use of Vulkan ray tracing.

It’s also one of relatively few Nvidia graphics technologies that doesn’t actually require a Nvidia GPU: supported cards includes AMD’s new Radeon RX 6000 Series GPUs.

The Attic demo: turn technologies like RTXGI, NRD and DLSS on and off in real time
While the RTXDI video is technically impressive, it’s very much a programmer’s demo. For a greater degree of visual polish – and for something you can actually play with – check out The Attic scene.

It’s a standalone executable built on Nvidia’s experimental RTX branch of Unreal Engine, and enables users to navigate Nvidia’s beautiful USD Attic sample scene in real time.

Anyone with a compatible GPU can toggle individual ray tracing effects, including RTXGI and NRD, on and off, making it possible to see their effects on the scene in isolation.

Nvidia describes RTXGI as a high-performance multi-bounce – or even infinite-bounce – indirect lighting system that avoids the technical issues created by the need to bake GI.

NRD is an API-agnostic spatio-temporal denoising library designed to work with low-ray-per-pixel signals.

As well as the new SDKs, The Attic demo also shows off effects available in public builds of Unreal Engine, including real-time ray traced shadows and reflections, plus deep-learning-based anti-aliasing technology DLSS, available as a free plugin for UE 4.26.

System requirements and availability
The Attic demo is available as a both a standalone executable and project files.

You will need a compatible Nvidia GPU to run it: ideally an RTX card, although it will run – albeit slowly – on GPUs as old as the GeForce GTX 10 Series.

The RTXDI and RTXGI SDKs are available via the Nvidia Developer program, and are integrated into the RTX Branch of Unreal Engine.

The RTXDI SDK is compatible with Windows 10 and any GPU supporting DXR 1.0+ or Vulkan with the Vulkan KHR_ray_query or KHR_ray_tracing_pipeline APIs.

The RTXDI SDK is compatible with Windows 10 and requires a Nvidia DXR-enabled GPU.

Download Nvidia’s The Attic GPU ray tracing tech demo

Read more about RTXDI on Nvidia’s Developer website

Read more about RTXGI on Nvidia’s Developer website