RTX Direct Illumination (RTXDI)

Imagine adding millions of dynamic lights to your game environments without worrying about performance or resource constraints. RTXDI makes this possible while rendering in real time.

Geometry of any shape can now emit light and cast appropriate shadows: Tiny LEDs. Times Square billboards. Even exploding fireballs. RTXDI easily incorporates lighting from user-generated models. And all of these lights can move freely and dynamically.

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  • You can ray trace area light shadows for only a limited number of lights, even with the most powerful GPUs on the market.
  • Typically 2-16 of the “most important” lights in AAA RTX titles, up to 100 lights in Quake 2 RTX and Minecraft RTX.
  • Up to millions of dynamic lights in real-time.
  • Lights made of ‘true geometry’. Any object in a game can emit light and cast dynamic shadows. Enables entire new class of content.
  • One shadowing algorithm: RTXDI replaces all other shadow and ambient occlusion techniques.

True Geometry For Lights

No more need for fake proxies. A more realistic simulation allows artists to create environments that approach photorealism. Lights with complex shapes, such as neon signs, work as they do in the real world.

Works as an Oracle for Shadow Rays

RTXDI tells the renderer where to send rays. Reducing the manual tuning required to light scenes will improve the efficiency of any art pipeline.

No More Hero Lights

Every light is a shadow caster. Scenes look richer and more grounded. Real-time renderings now reach the complexity level that only baked backgrounds previously allowed.

Built to be Paired with RTXGI

Can be combined with RTXGI for fast and scalable global illumination with many lights. RTXDI provides great results on its own, while amplifying the value of other NVIDIA ray tracing SDKs.

RTXDI Comparison to Prior State of the Art Techniques

Photo courtesy of artist GoldSmooth & TurboSquid

The image on the left uses prior state-of-the-art technique sampling techniques. The image on the right uses RTXDI, which can generate a finished image with the same level of overhead. Both images were constructed with equal time, using an equal number of rays per pixel.

Player Benefits

  • Environments that are directly lit by a vast array of sources can be simulated in a manner that feels grounded and looks realistic. Imagine capturing every direct light in a city night scene, a carnival scene, etc.
  • Having more lights to work with allows players and NPCs to turn on/turn off/shoot out lights to affect visibility in regions of the game.
  • RTXDI helps real-time ray traced games reach visual parity with CG animated film scenes that use 8M+ lights simultaneously.

Game Artist Benefits

  • Brilliant real-time ray tracing results, even when working with a very limited ray-per-pixel count.
  • Artists are no longer limited by the number of lights they can use to author a real-time environment.
  • RTXDI automatically determines where to send rays.


 A: RTXDI is a software development kit that leverages the power of GPU ray tracing to provide a scalable solution for the computation of direct illumination and shadows for scenes involving millions of light sources in real-time.

 A: Yes! The ability to trace arbitrary rays is critical for rendering scenes with shadows from millions of lights without the use of shadow maps.

 A: RTXDI supports thousands to millions of dynamic area light sources in real time without requiring a high-maintenance data structure or offline preprocessing. Support for millions of area lights means that any mesh can be broken down into triangles, and each triangle can emit light into the scene. Such mesh would cast realistic lighting and shadows onto the objects around it, including self-illumination and self-shadowing if some parts of the mesh are not emissive.

 A: RTXDI supports mesh lights as well as regular “primitive” lights, such as spheres, spot lights, rectangular lights etc, as well as "infinite" lights, such as environment maps and directional lights like the sun. Mesh lights are just any objects in the scene that have an emissive component in their material that can be evaluated before rendering the scene. So, artists do not need to do anything extra in order to make their scenes lit by mesh lights (depending on the RTXDI implementation in a particular engine).

 A: The RTXDI SDK is a full source distribution. The SDK includes the complete C++ and HLSL source code of the SDK, as well as documentation for the SDK code. A full source sample application that demonstrates how to use the SDK will also be included.

 A: The RTXDI SDK supports the DirectX Raytracing (DXR) API version 1.0 and 1.1 for DirectX12 , and Vulkan Ray Tracing via the VK_KHR_ray_query and VK_KHR_ray_triacing_pipeline APIs on Windows.

 A: RTXDI works on any GPU with support for the DirectX Raytracing or Vulkan Ray Tracing, including all NVIDIA RTX 30 series and RTX 20 series GPUs.

 A: RTXDI will be made available as part of the NvRTX UE 4.26 branch. No current plans regarding Unity.


Ready to get started developing with RTXDI?

Get Started with RTXDI