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ScriptableRenderPipeline/Core/ShaderLibrary/ImageBasedLighting.hlsl

             // TODO: use a Gaussian-like filter to generate the MIP pyramid.
             float3 val = SAMPLE_TEXTURECUBE_LOD(tex, sampl, L, mipLevel).rgb;
 
-            // Our goal is to use Monte-Carlo integration with importance sampling to evaluate
+            // See "Moving Frostbite to Physically Based Rendering", p 63.
+            // The goal of this function is to use Monte-Carlo integration to evaluate
+            // Note: Integral{CBSDF(L, N, V) dL} is given by the FDG texture.
             // CBSDF  = F * D * G * NdotL / (4 * NdotL * NdotV) = F * D * G / (4 * NdotV).
             // PDF    = D * NdotH / (4 * LdotH).
             // Weight = CBSDF / PDF = F * G * LdotH / (NdotV * NdotH).