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ReSTIR Path Tracing (ReSTIR PT)

Introduction

This repo includes the source code for the following SIGGRAPH 2022 paper

Generalized Resampled Importance Sampling: Foundations of ReSTIR<br> Daqi Lin* (University of Utah), Markus Kettunen* (NVIDIA), Benedikt Bitterli (NVIDIA), Jacopo Pantaleoni (NVIDIA), Cem Yuksel (University of Utah), Chris Wyman (NVIDIA)<br> (*Joint first authors) <br> https://graphics.cs.utah.edu/research/projects/gris/ (with embedded interactive viewer and video) https://research.nvidia.com/publication/2022-07_generalized-resampled-importance-sampling-foundations-restir

ReSTIR Path Tracing (ReSTIR PT) is a resampling-based path tracing algorithm as the result of applying the GRIS theory to ReSTIR. Compared to ReSTIR GI [Ouyang et al. 2021], ReSTIR PT handles general types of light transport. The path reuse quality is significantly improved by a context-aware shift mapping, allowing interactive rendering of many-bounce diffuse and specular lighting with high quality.

The method is implemented as a render pass called "ReSTIRPTPass" (Source\RenderPasses\ReSTIRPass) in Falcor 4.4. See README_Falcor.md for the original README file provided by Falcor.
A script RunReSTIRPTDemo.bat is provided to show how the method works in an animated version of the 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.

Prerequisites

Windows 10 version 20H2 or newer
Visual Studio 2019
[Windows 10 SDK version 10.0.19041.1 Or Newer] (https://developer.microsoft.com/en-us/windows/downloads/sdk-archive)
NVIDIA driver 466.11 or newer
RTX 2060 or Higher (NVIDIA graphics card with raytracing support)
Get NVAPI, head over to https://developer.nvidia.com/nvapi and download the latest version of NVAPI. Create a folder called .packman under Source/Externals, Extract the content of the zip file into Source/Externals/.packman/ and rename Rxxx-developer to nvapi.

How to compile

Make sure you have NVAPI in Source/Externals/.packman/
Open Falcor.sln and Build Solution in configuration ReleaseD3D12

Run the demo

execute RunReSTIRPTDemo.bat
The GUI contains self-explanatory settings to turn on/off different components of ReSTIR PT or change its quality.

Test with more scenes

You can test your custom scene by running Bin\x64\Release\Mogwai.exe first, then load a scene file.
A Falcor pyscene is recommended. For how to create a pyscene, please check out the Source/RenderPasses/ReSTIRPTPass/Data/VeachAjar/VeachAjar.pyscene as a template. Details can be found in Falcor's documentation
Alternatively, if you have a scene file with well defined lighting, material, and camera information that is supported by Falocr (like FBX), you can also create a one-line pyscene file, e.g. sceneBuilder.importScene(YOUR_SCENE_FILE).

Offline rendering

ReSTIR PT is an unbiased algorithm and can be used for offline rendering. The recommended setting is to disable temporal reuse, use 32 candidate samples per pixel, and set the number of spatial reuse rounds, spatial neighbors, and spatial reuse radius to 3, 6, 10, respectively (more details in the paper).