@Deltakosh @Sebavan @PatrickRyan
Hi, Thank you for your kind response to my friend @cx20. I'm impressed that Babylon.js is doing a lot of efforts to verify the reflection model. Recently, I started to add support of PBR to my library (still only punctual light).
Let's say that Cook-Torrance base is good for the model of specular reflection.
I was worried about which specific approximation formula is appropriate (Disney, Unreal Engine, Frostbite, Major companies, each best practice exists). Of course, I was also concerned about the handling of roughness etc.
I immediately looked at the Khronos official PBR sample, and I decided to make the implementation almost the same for the time being. I wanted to avoid the result of my library getting away from other libraries, so I expected each library to reference it as a reference.
But, according to cx20's comparison test (He is comparison test happy! ), The results of each library seem to be very different. And, in actual use of glTF 2.0, differences in PBR results which can be seen even at amateur level among each library seems to cause people a lot of confusion. For the general public, there are no interests in internal mathematics, and the brightness and color taste of what they saw are all.
I think there are some key points of view.
* What is the renderer that each library refers to? (btw, I started to refer Arnold Renderer too. It's unbiased renderer, popular, and default solution in Autodesk DCCs. Of course those do not mean that all results are correct proof...)
* A case where the validity of energy conservation etc collapses as design and implementation become more complicated (such as clear coat support)
* Simply, careless mistake in handling gamma (recently, there was a thing in a major library)
* Difference in approximate expression to select (In a sensitive case, the difference in reflection lobes and spikes may appear in visual results. for example, In Unreal Engine etc, they started to use Height-Correlated Smith Masking and Shadowing function.)
* Difference of IBL implimentation
Even with local reflections, the results differ so much, so in the future, gIobal Illumination results will be more different between each library.