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hdRstr ray traces thousands of area lights in real time

Tuesday, September 14th, 2021 | Posted by Jim Thacker

A scene with mesh lights totalling over 27,000 emissive triangles, rendered in the Houdini viewport on a Nvidia GeForce RTX 2070 GPU via new render plugin hdRstr. See a more typical real-world set-up here.

Tools developer Stefan Krake has unveiled hdRstr, an interesting new add-on that enables artists to work with “tens of thousands” of area lights in real time in the viewport of Maya or Houdini.

The software, which is based on RTXDI, Nvidia’s new direct illumination system for GPU ray tracing, is currently available in free open beta.

Edit complex lighting set-ups inside Maya and Houdini in real time
hdRstr makes it possible to edit very complex lighting set-ups for visual effects or animation work interactively inside the viewports of DCC applications.

The software uses a number of new Nvidia GPU ray tracing SDKs to compute the illumination generated by “tens of thousands” of mesh-based lights in real time.

The main one is RTXDI, Nvidia’s implementation of its ReSTIR sampling algorithm, which handles the direct illumination in a scene, along with NRD to denoise the result.

We covered both technologies they were demoed at GTC 2021, so check out this story for more details.

Displays direct lighting, with some limited support for indirect illumination
hdRstr is primarily intended to provide a high-speed preview when editing a lighting set-up, providing a “good approximation” of the final direct lighting in a scene in real time.

Although it can display indirect lighting to some extent – users have the option to enable a single light bounce – that’s really a job for other viewport renderers, with which it is designed to be used in parallel.

Implemented as a Hydra render delegate, but not just for USD workflows
The software is implemented as a Hydra render delegate and supports key features of Pixar’s Universal Scene Description (USD), of which Hydra is the rendering framework.

That includes the UsdPreviewSurface preview material with a metallic/roughness PBR workflow, and “most” UsdLux light types.

In Houdini, hdRstr can really only be used as part of a USD workflow, since Hydra render delegates are only supported inside Solaris, the software’s new USD-based lighting and lookdev environment.

However, in Maya, it can be used as a replacement for Viewport 2.0, even for non-USD-based workflows, providing that you have the Maya USD plugin installed.

Works with both Nvidia and AMD GPUs, but currently only on Windows
hdRstr uses Microsoft’s DXR API for hardware-accelerated ray tracing, so it currently only works in Windows.

Support for the Vulkan and its new Ray Tracing extensions is “technically possible and doable”, so Krake plans to release a Linux version, but a macOS edition is less likely.

Pricing and system requirements
hdRstr is currently available as a free open beta for Houdini 18.5 and Maya 2022+ on Windows 10 only.

It requires a GPU that supports DXR, which includes AMD’s Radeon RX 6000 and Radeon Pro W6000 cards, although it has mainly been tested with Nvidia’s RTX GPUs.

The commercial release of the Houdini edition is scheduled for later this month, while the Maya edition is scheduled for a commercial release early in October 2021.

Read more about hdRstr for Maya and Houdini on Stefan Krake’s website

Download the free open beta of hdRstr from GitHub

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