In the past period of time, I have been learning about pbr materials.
Based on Cook-Torrance BRDF, we usually assume that when a beam of light collides with the surface of the material for the first time, if it does not enter the observer’s eyes, it disappears and will never enter the observer’s eyes. This is why energy is not conserved when performing the white furnace test.
I have consulted relevant information about multiple scattering and have seen many solutions for the implementation of multiple scattering. In the sharing of A Journey Through Implementing Multiscattering BRDFs and Area Lights at SIGGRAPH2019, I saw the solution used by threejs and the improved solution based on this. However, I found that when calculating IBL multiple scattering, the sharer even calculated the contribution of the diffuse term. This is not done in threejs and filament. Why is this? Is it because his contribution to diffuse reflection is so small that it can be ignored?
This is based on the paper About IBL of Multiple Scattering in THREEJS. In the demo, I saw that he calculated the diffuse contribution of Multiple Scattering, which puzzled me.