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# Tag Info

## Hot answers tagged microfacet

7 votes
Accepted

### Correct form of the GGX geometry term

TL;DR: Your $G1$ formula is wrong. Just to avoid confusion, I am assuming the isotropic version of the BRDF, the Smith microfacet model (as opposed to the V-cavity model), and the GGX microfacet ...
• 1,464
3 votes

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

The units of the NDF are tricky. For whatever it's worth, Heitz's convention of defining it relative to a 1 m² reference geometric surface is unusual, and although I can see why he would want to ...
• 25k
3 votes
Accepted

### Why can I see the diffuse lighting effect on a perfect mirror?

Dielectric materials (which is what you get when metalness is 0) don't exhibit a mirror-like effect. Think of a sheet of smooth, non-transparent plastic. Real-life mirrors are panes of glass or ...
• 892
3 votes
Accepted

### Can't understand the Importance sampling GGX

In microfacet BRDFs, the half-vector is the same as the microfacet normal. The half-vector is exactly the required normal for a microfacet to reflect light from the incident ray to the outgoing ray, ...
• 25k
3 votes
Accepted

### Relationship between roughness and BRDF

Most normal distribution functions (NDFs) are parametrized by some variable (tipically $m$ or $\alpha$) that determines the "roughness" or "spikiness" of the NDF (this is often meant to be the rms ...
2 votes

### Relationship between roughness and BRDF

for each point $p$ in theory we have a 3D function that tells us the orientation in a given direction You have missunderstood this. $D$ is a Normal Distribution Function (or short NDF), so it doesn't ...
• 1,566
2 votes

### Can microfacet BRDF (including ggx) represent perfect mirror?

If this was correct, $\frac{D(H)G(L,V,H)}{4|N⋅V|}$ should be a dirac delta function. But I don't think so. Actually, you're close to your answer - you just are trying to find out, what the assumption ...
• 1,566
2 votes

### Implementing the example of Walter et al. (2007) paper

Initially and still I'm not so sure how to get the color of the object behind the glass into the formulas. Normal, this was written with path / ray tracers in mind where that part is easy. Your idea ...
• 1,585
2 votes
Accepted

### What does GGX stand for?

According to E. Heitz (Sampling the GGX Distribution of Visible Normals) it stands for "ground glass unknown". I am not sure what the word unknown means though. By the way, it is equivalent ...
2 votes
Accepted

### Importance sampling microfacet BRDF and coordinate frame

The importance sampling methods for the two reflection models you mentioned are different - they pretty much reflect their definition. Cook-Torrance model describes the surface as a collection of ...
1 vote
Accepted

### How is the distribution of normals constructed from the distribution of slopes in 'Understanding the masking-shadowing function' paper?

The "slope space" is a coordinate system that describes unit vectors in the upper hemisphere using their $x$ and $y$ slopes, i.e. $-x/z$ and $-y/z$. It's related to the usual polar ...
• 25k
1 vote
Accepted

• 25k
1 vote
Accepted

### Microfacet BRDF artifacts

It turns out that the ring was happening from a negative divided by a negative, so adding nom = max(nom, 0.0); fixed the problem. The new highlight, amplified:
• 198
1 vote

### Can microfacet BRDF (including ggx) represent perfect mirror?

I actually have stumbled at this same exact problem. I think I have found the solution in the pbr book: https://www.pbr-book.org/3ed-2018/Reflection_Models/Microfacet_Models#...
• 11

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