Wrong microfacet BTDF formula used in reflection.cpp? #108

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TzuChieh opened this Issue Jan 10, 2017 · 0 comments

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@TzuChieh

I noticed that in the paper written by Walter et al. (Microfacet Models for Reflection through Rough Surfaces), the microfacet BTDF formula (equation 21) has an eta_o^2 term in the numerator; while in PBRT-v3 book P.548 equation 8.20 it has an eta_i^2term instead (source code seems to follow this). Actually some rendering artifacts in my hobby renderer are fixed by using PBRT's formula, but the inconsistency between PBRT and the original paper makes me curious. Or am I missing some impoortant concepts here?

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