Walk-on-Boundary on PBRTv3

This is an extension of PBRT version 3 that implements our SIGGRAPH NA 2023 paper, A Practical Walk-on-Boundary Method for Boundary Value Problems by Sugimoto, Chen, Jiang, Batty, and Hachisuka. Specifically, this is the codebase used to generate the figure featured in section 5.3, WoB within MC rendering. This codebase only implements a solver for the interior Dirichlet problem.

Directory structure

All of the relevant extension code is contained within the src/wob subfolder. In particular:

• wob.cpp and wob.h: Main implementation of the extension through the WobIntegrator class (specifically WoBIntegrator::Li)
• scenes: Example scenes used in rendering. The figure in the paper used the bunny scene.
• thirdparty: Dependency libraries

Additional modifications were made to src/core/api.cpp to integrate the new WoBIntegrator class, src/core/film.h to expose private methods, src/core/geometry.h to fix zero vector normalization, and src/core/integrator.h to disable negative luminance checks.

Dependencies

C++ dependencies

As with base PBRT, C++ dependencies are included as git submodules.

git clone --recurse-submodules https://github.com/tyxchen/WoBonPBRTv3.git

There is only one external C++ dependency:

• tinycolormap: a header-only library for colormaps

Python dependencies

Running the turnkey render script (as described below) requires the following:

• Python 3.9+
• matplotlib
• numpy
• pandas

Building and rendering

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make pbrt_exe

Due to how PBRT is architected, the solution must be rendered separately from the scene; the separate renders must then be composited to produce the final image. To render and composite the bunny example:

python3 render.py src/wob/scenes/bunny.pbrt --pbrt build/pbrt --render-scene

This will produce the following files:

• bunny.png: the interior solution as rendered by PBRT
• bunny.png.mask: a mask file for compositing
• bunny.png.txt: the raw numerical solution as rendered by PBRT
• bunny-scene.png: the rendered background scene
• bunny-plt.png: the final composited image

Subsequent runs can skip rendering the background scene by removing the --render-scene flag.

Credits

PBRT version 3 is released by Matt Pharr, Wenzel Jacob, and Greg Humphreys under the BSD license.

The watertight Stanford Bunny model included in this repository is courtesy of Christopher Batty.