9/22 Multiple Importance Sampling + GGX

Slight update to mis progression. The individual parts (nee and brdf) render and match the reference. Now the hard part is combining the two into one function. The current renders looks as follows.

NEE
With next event estimation, rough surfaces get rendered better but have an issue when it comes to rendering shiny surfaces.

BRDF
With brdf, shiny sources render better and the reflection is clear. So the goal of mis is to combine the two of these.

While in the process of making these two images, there were a few clamping issues that were fixed which reduced the black spots that appeared for the ggx render.
Due to the domain of arccos function, it just needed to be clamped to [-1, 1] to avoid Nan values.



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