Chapter 20. GPU-Based Importance Sampling

Because BRDFs are a part of the integration, they serve as a good measure to guide the simpling to produce directions that best approximate the integral. Here, we use a normalized BRDF as the PDF for sampling. To sample this PDF, we convert a random number pair into an important direction for the BRDF.

注意此时求出来的 specular direction 朝向 z 轴

$$ \theta_s = P^{-1}(Uniform Sampling) $$