RTX Direct Illumination (RTXDI)

RTXDI offers realistic lighting of dynamic scenes that require computing shadows from millions of area lights. Until now, this has not been possible in video games. Traditionally, game developers have baked most lighting and supported a small number of “hero” lights that are computed at runtime.

With RTXDI, lighting artists can render scenes with millions of dynamic area lights in real-time without complex computational overheads or disruptive changes to the artist’s workflow. Imagine a night city scene from a 10th story view with streets full of moving cars, moving people, moving bicycles, etc: Millions of lights visible through windows, street lights, traffic lights, landscape/building lights, etc. All of that can now be captured in real-time with RTXDI.

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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.

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. 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, other than maybe tag some important lights in the scene (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 1.1 for DirectX12 on Windows.

 A: RTXDI works with any DXR enabled GPU. This includes all NVIDIA RTX 30 series and RTX 20 series.

 A: We’re aiming at the first release in 2021.

 A: We plan to develop and release a UE4 implementation of RTXDI. No current plans regarding Unity.

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