hdRstr will become open source! (but no ETA yet...) Learn more
Check out the brand new blRstr for Blender with shading network support! Learn more
Coming soon: MaterialX support! And more bounces (like blRstr)!

hdRstr: A ReSTIR/RTXDI-based Hydra Render Delegate.

Direct lighting from tens of thousands of lights with real-time frame rates directly inside the viewport.

  • ReSTIR[1]-based direct lighting. Uses Nvidia's RTXDI[2] implementation for maximum speed and quality.
  • High quality real-time denoising using ReLAX from Nvidia's NRD[3] SDK.
  • Optional 1-bounce indirect lighting accelerated with ReSTIR.
  • Arbitrary emissive geometry ("mesh lights") and emissive textures.
  • UsdPreviewSurface with metallic and specular workflow. Most UsdLuxLight types*.
  • Works with SideFX's Houdini 18.5 and Autodesk Maya 2022
  • Requires Windows 10 with DXR 1.1 (Linux/Vulkan planned).
  • DXR-capable GPU required. RTX 2070 or higher recommended.
For updates follow @stkrake on github or twitter or blog.stkrake.net.
The sources will be published on github when ready.


  1. What's the use case?

    The primary intent is a very fast viewport renderer, that is able to show a good approximation of the final direct (and more limited indirect) lighting in real-time. It is designed to be used alongside other viewport renderers.

  2. Is it for USD only?

    Maya: No. Hydra render delegates can be used as VP2 replacement. Only the official maya-usd plugin is needed. There may be limitations for some materials and lights.
    Houdini: Sort of. Hydra render delegates are only active in the Solaris view (/stage). It can not be used to directly render non-LOP nodes.

  3. Could it be used for production rendering?

    Maybe. If the quality is good enough for a production it could certainly be used as a final renderer. People are using game engines for production rendering now, and they seem to be happy with the very limited lighting capabilities. Expect game engine quality with much, much better lighting.

  4. Why is it so much faster than anything before?

    Call it scientific and/or technical progress. Without real-time ray tracing there was no real need for very fast light sampling. Then the inventors of ReSTIR[1] looked at Monte Carlo methods previously not used in path tracing and found a way to improve it vastly (at the expense of some precision). And the RTXDI[2] and NRD[3] developers made it production-ready.

  5. Is it Nvidia only?

    No. It should run on any hardware supporting DXR 1.1 (or the Vulkan Ray Tracing Extensions, see below). Practically there are currently not much devices from other vendors available or in use, so this is not really tested.

  6. Does it run on Linux?

    This is planned. A Vulkan-based version is technically possible and doable.

  7. Will it run on macOS?

    Tricky. One would need to use Vulkan with MoltenVK, which does not seem to support ray tracing. But in theory it could go like this: Most shaders are just compute shaders working on buffers. This part should work with MoltenVK. The ray tracing part just fills a G-Buffer. This could be separately done with Metal (indirect lighting currently traces rays "on the fly" from a compute shader, but this could be redesigned). So, if there is enough demand (and ray tracing hardware), it may be worth a try. But at the moment there a no plans.


1. Benedikt Bitterli, Chris Wyman, Matt Pharr, Peter Shirley, Aaron Lefohn, Wojciech Jarosz. Spatiotemporal reservoir resampling for real-time ray tracing with dynamic direct lighting. ACM Transactions on Graphics (Proceedings of SIGGRAPH), 39(4), July 2020. DOI:https://dl.acm.org/doi/10.1145/3386569.3392481. Link to author's version.

2. RTX Direct Illumination (RTXDI).

3. NVIDIA Real-Time Denoisers.

* UsdLuxCylinderLight, UsdLuxDiskLight, UsdLuxDistantLight, UsdLuxDomeLight, UsdLuxRectLight, UsdLuxSphereLight and UsdLuxGeometryLight.
hdRstr: A ReSTIR/RTXDI-based Hydra Render Delegate (maya demo, RTX 2070)
hdRstr: A ReSTIR/RTXDI-based Hydra Render Delegate (colorful demo, RTX 2070)
hdRstr: A ReSTIR/RTXDI-based Hydra Render Delegate (serious demo, RTX 2070)
Scene: Amazon Lumberyard Bistro, Open Research Content Archive (ORCA)