Conditional ReSTIR Prototype

Introduction

• This repo includes source code for the following SIGGRAPH Asia 2023 paper

Conditional Resampled Importance Sampling and ReSTIR
Markus Kettunen* (NVIDIA), Daqi Lin* (NVIDIA), Ravi Ramamoorthi (NVIDIA and UC San Diego), Thomas Bashford-Rogers (University of Warwick), Chris Wyman (NVIDIA)
(*Joint first authors)

This prototype application of conditional ReSTIR defers ReSTIR-based path reuse by one or more bounces. It is based on conditional resampled importance sampling (CRIS) theory, an extension of GRIS [Lin et al. 2022] to conditional path spaces that enables reusing subpaths from unidirectional-sampled paths with correct unbiased contribution weights. Our conditional ReSTIR prototype modifies ReSTIR PT [Lin et al. 2022] with a final gather pass. As in photon mapping, such a final gather reduces blotchy artifacts from sample correlation.

• The method is implemented as a rendering component called "ConditionalReSTIR" (Source/Falcor/Rendering/ConditionalReSTIR) in Falcor 5.2. See README-Falcor.md for the original README file provided by Falcor.
• A script runConditionalReSTIRDemo.bat is provided to show how the method works VeachAjar scene (from Benedikt Bitterli's rendering resources) which is contained in the repo.
• Before running the scripts, you need to compile the program and download the scene files following the instruction below.

Licensing

The new conditional resampling code in this repository is licensed under the NVIDIA Source Code License. Included NVIDIA dependencies remain licensed under their existing licenses, including: Falcor, DLSS, RTXGI, RTXDI, and NRD.

Falcor also downloads various 3rd party dependencies as git submodules; these have their own licenses.

Prerequisites

• Windows 10 version 20H2 or newer
• Visual Studio 2022
• Windows 10 SDK version 10.0.19041.1 Or Newer
• We relied on NVIDIA drivers 530.xx and above
  • Though our baseline Falcor only requires NVIDIA driver 466.11 or later
• A GPU supporting DirectX Raytracing
  • Conditional ReSTIR is very costly; we recommend a NVIDIA GeForce RTX 4090 if planning to play with settings much

How to compile

IMPORTANT: We use git submodules to download dependencies! Downloading the git repository as a .zip (rather than using git clone) will ensure you lack required dependencies, and the build scripts will fail.

After cloning the repository:

• Run setup_vs2022.bat
• Open build/windows-vs2022/Falcor.sln and the Build Solution in the Release configuration

Run the demo

• Execute runConditionalReSTIRDemo.bat
• The GUI contains self-explanatory settings for parameter tweaking under "Rendering Presets".
• Not all exposed options under other, more advanced, menus work together in all configurations (e.g., at least Falcor's existing path tracing "Russian roulette" toggle is known buggy).

Testing with more scenes

To run our code more generally requires:

• Running the executable build/windows-vs2022/bin/Release/Mogwai.exe
• Loading the conditional ReSTIR render script scripts/ConditionalReSTIR.py. Options include:
  • Drag and drop the script into a running Mogwai instance
  • Load via a Mogwai menu (File -> Load Script), or
  • Pass to Mogwai as an command line parameter (as in runConditionalReSTIRDemo.bat)
• Loading a scene:
  • The last line of the ConditionalReSTIR.py script already does this
  • Modify this line, if desired, or delete it and load the scene explicity via drag-and-drop or the Mogwai menus.

Mogwai can load a variety of scene types:

• Falcor's native .pyscene format (more details).
• Some simplistic .usd files (support is largely experimental).
• FBX files and GLTF files via the included Assimp module.
  • Many of these lack emissive light surfaces, which are important for ReSTIR renderers.
  • Often we wrap these in a .pyscene file so we can modify material emissive properites via Python on load.
• Many PBRT v4 files:
  • E.g., from Benedikt's resources page
  • Though not all materials match with PBRT.