# Questions tagged [microfacet]

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### Does sampling GGX VNDF take into account the cosine incidene of outgoing ray?

Could sampling GGX VNDF sampling, based on: "Sampling Visible GGX Normals with Spherical Caps" and "Sampling the GGX Distribution of Visible Normals" produce a normal that (based ...
• 720
0 votes
1 answer
129 views

### What does GGX stand for?

Many render engines implement the microfacet model for rendering surfaces that are rough, metallic, and/or transparent, a concept first published in "A Reflectance Model for Computer Graphics&...
1 vote
1 answer
63 views

### Importance sampling microfacet BRDF and coordinate frame

I'm trying to importance sample the Cook Torrance BRDF for my path tracer but I'm not sure about the part where you have to change the sample from one coordinate frame to another. This resource states ...
• 113
1 vote
1 answer
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### How is the distribution of normals constructed from the distribution of slopes in 'Understanding the masking-shadowing function' paper?

Recently I'm reading Eric Heitz's paper 'Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs', in section 5, 5.2, the paper defines the distribution of slopes and then says the ...
1 vote
0 answers
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### Why my bsdf can not pass Chi2test?

I implemented a MicrofacetTransmission in nori. But it can not pass all Chi2test when alpha is large(>= 0.4 or ?),part of chi2test is passed.And I can not found the problem.Can someone help me? ...
• 31
1 vote
1 answer
132 views

### Conflicting definitions for the distribution of normals $D$ in microfacet BSDFs

Please do not confuse this question with this one. In Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs, Eric Heitz defines the distribution of normals as. There, the footnote. ...
2 votes
1 answer
233 views

### How is the maximum value for alpha (roughness == 1) decided for microfacet models?

Recently I have been looking at pbrt, and was looking at their remapping from roughness to $\alpha$ values: https://github.com/mmp/pbrt-v3/blob/master/src/core/microfacet.h#L86 I understand that it is ...
3 votes
1 answer
170 views

• 526
12 votes
1 answer
5k views

### Correct form of the GGX geometry term

I'm trying to implement a microfacet BRDF in my raytracer but I'm running into some issues. A lot of the papers and articles I've read define the partial geometry term as a function of the view and ...
• 123
11 votes
1 answer
878 views

### Compensation for energy loss in single-scattering microfacet BSDF models

Single-scattering microfacet-based surface models like the original Torrance-Sparrow BRDF or derived models like the BSDF for rough dielectric surfaces by Walter et al. neglect inter-reflection of ...
• 1,424
10 votes
1 answer
473 views

### How does Smith multiple scattering interact with diffuse subsurface scattering?

The Multiple Scattering Microfacet BSDFs with the Smith Model paper describes a statistical model for replacing the masking-shadowing functions in microfacet BSDFs (which account for paths with more ...
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