RTX Direct Illumination (RTXDI)

Imagine adding millions of dynamic lights to your game environments without worrying about performance or resource constraints. NVIDIA RTX? Direct Illumination (RTXDI) figures out the most important light samples in a scene and renders them physically accurate. Geometry of any shape can emit light, cast appropriate shadows, and move freely and dynamically.

Access RTXDI     Introductory Resources

RTXDI Product Benefits

True Geometry for Lights

RTXDI samples primary and secondary shadow rays and as many continuation rays you want. This allows artists to create photorealistic environments with physically accurate lighting.

Fast Integration. Low Cost.

Quickly implement millions of ray traced dynamic lights without manual tuning. These lights cast accurate shadows with low performance overhead.

Built for Real-Time Path Tracing

RTXDI combines with our suite of RTX and Neural rendering technologies to build a real-time path tracer, handling screen space and world space light sampling and path reuse.

RTXDI Off and On Comparison


  • You can ray trace area light shadows for only a limited number of lights, even with the most powerful GPUs on the market.
  • Typically only 2-16 of the “most important” lights in AAA RTX titles—and up to 100 lights in Quake 2 RTX and Minecraft RTX—can be ray traced.


  • With RTX on, you can ray trace up to millions of dynamic lights in real time.
  • Lights are made of “true geometry.” Any object in a game can emit light and cast dynamic shadows, enabling an entirely new class of content.
  • There’s only one shadowing algorithm: RTXDI replaces all other shadow and ambient occlusion techniques.
Ray trace area light shadows for only a limited number of lights with RTXDI off Ray trace up to millions of dynamic lights in real time with RTXDI on

Importance Sampling Algorithms

ReSTIR or spatiotemporal reservoir resampling samples one-bounce direct lighting from many lights without needing to maintain complex data. ReSTIR DI samples all primary lighting and shadows in the screen space 65x faster than the previous state of the art solution (RIS or resampled importance sampling). This screen space light sampling solution is capable of virtually unlimited lights with a few (1-4) rays per pixel.

This image shows native Path Tracing This image shows ReSTIR DI and Path Tracing together

ReSTIR GI resamples multi-bounce indirect lighting paths. At a single sample per pixel every frame, this solution achieves a mean-square error (MSE) improvement greater than 10x. In conjunction with a denoiser, this offers high quality path tracing at real-time frame rates.

This image shows native Path Tracing This image shows ReSTIR GI and Path Tracing together

Comparing RTXDI to Other State-of-the-Art Techniques

Prior sampling technique in theater sceneRTXDI in theater scene

Photo courtesy of artist GoldSmooth & TurboSquid

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

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

 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, and rectangular lights, 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 don’t need to do anything extra to light their scenes with 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 is also included.

 A: The RTXDI SDK supports DirectX Raytracing (DXR) API versions 1.0 and 1.1 for DirectX12 , as well as Vulkan Ray Tracing via the VK_KHR_ray_query and VK_KHR_ray_tracing_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: Yes, RTXDI is supported in the latest Unreal Engine 4 and 5 NvRTX branches. There are no current plans for Unity.

Ready to start developing with RTXDI?