Questions tagged [ggx]

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Explanation of math of the Smith G1 term

In appendix A of the paper Microfacet Models for Refraction through Rough Surfaces there is a derivation provided for $\Lambda(w)$ but the mathematics is very confusing. Could somebody help me by ...
3
votes
0answers
94 views

IBL looks too dark with uniform sampling

I'm making a program that illuminates a sphere using an environment map. For each fragment in the sphere, I compute a many random directions in the hemisphere along the surface normal (no importance ...
2
votes
0answers
86 views

Do all microfacet brdf models diverge at grazing angle?

My question follows directly this one. Reading the famous paper of Walter, it comes that the plotted curves of figure 13 (in question in the related topic) are not directly the brdf but rather the ...
2
votes
0answers
115 views

Comparing different sampling methods for GGX IBL

I have made a demo that shades a sphere with an environment map. I wanted to compare 3 different ways of sampling the environment. Uniform sampling. Importance sampling with the NDF as suggested in ...
1
vote
0answers
48 views

How to handle negative reflection directions in raytracing?

I got a function that generates samples from a GGX visible normal distribution function. When I use it to calculate reflection directions obviously some of these intersect with the surface agin (...
1
vote
0answers
465 views

GGX BRDF is greater than 1?

I am implementing a GGX BRDF, this is the formula I used is from:https://schuttejoe.github.io/post/ggximportancesamplingpart1/ And this is my implementation: ...
0
votes
0answers
44 views

Raytracing, divide by PDF neutralized the effect of D and G terms, what is the problem?

Following some documents on internet, I divide my ray tracing result by PDF. Then it seem the D and G terms disappeared. Only F term is still visible, it looks like Fresnel only. ...