pbrt-v3

Reference pbrt-v3 implementation

We provide reference implementations for our proposed LTC sheen BRDF, together with baselines and prior work.

Compilation

1. Clone the pbrt-v3 repository:

git clone --recursive https://github.com/mmp/pbrt-v3/

2. Copy over the contents of src from this repository into the respective cloned directory. Note that the file src/core/api.cpp needs to be overwritten.

3. Compile pbrt-v3 normally, e.g. on Unix:

mkdir build
cd build
cmake ..
make -j

See the original README for details.

List of implemented BRDFs

LTC Sheen

sheenltc.h / sheenltc.cpp Our LTC fits based on either the volumetric SGGX or analytic approximation as references.

Scene format example:

Material "sheenltc" "color Csheen" [1 1 1] "float alpha" [0.5] "string type" [<type>]

where <type> should be replaced with either "volume" or "approx" to select which version should be used.

Volumetric models

sheenvolume.h / sheenvolume.cpp The fiber-like SGGX volumetric model we used as inspiration/reference of our LTC fits.

Scene format example:

Material "sheenvolume" "rgb albedo" [1 1 1] "float density" [1.0] "float sigma" [0.25] "integer maxBounces" [16]

Setting the maxBounces parameter to 1 also gives the interesting single-scattering only case.

Prior work

sheenbaselines.h / sheenbaselines.cpp Various versions are implemented:

• type == "burley"

  The isolated sheen component of the principled BRDF presented in "Physically Based Shading at Disney" by Brent Burley in the Physically-based Shading course at SIGGRAPH 2012.

  Scene format example:

  Material "sheenbaselines" "color Csheen" [1 1 1] "string type" ["burley"]
  

• type == "neubelt_pettineo"

  Sheen model presented in "Crafting a Next-Gen Material Pipeline for The Order: 1886" by Neubelt and Pettineo in the Physically-based Shading course at SIGGRAPH 2013.

  This is a modified version of a previous model from "A Microfacet-based BRDF Generator" by Ashikhmin et al. 2000.

  Scene format example:

  Material "sheenbaselines" "color Csheen" [1 1 1] "float alpha" [0.5] "string type" ["neubelt_pettineo"]
  

• type == "conty_kulla"

  Sheen model presented in "Production Friendly Microfacet Sheen BRDF" by Conty and Kulla in the Physically-based Shading course at SIGGRAPH 2017.

  Scene format example:

  Material "sheenbaselines" "color Csheen" [1 1 1] "float alpha" [0.5] "string type" ["conty_kulla"]
  

• type == "patry"

  Sheen model presented in "Samurai Shading in Ghost of Tsushima" by Jasmin Patry in the Physically-based Shading course at SIGGRAPH 2020.

  Scene format example:

  Material "sheenbaselines" "color Csheen" [1 1 1] "float alpha" [0.5] "string type" ["patry"]
  

Test scenes

Two test scenes are included:

• The draped cloth example scene shown above: cloth.pbrt

• Directionally lit sphere sphere.pbrt

  The parameter <angle> in the scene description line

  Rotate <angle> 0 1 0
  

  can be used to change the angle of the directional light. The value is expected to be in degrees where 0 is front and 180 is back lighting.