# Tag Info

## Hot answers tagged ggx

### Dealing with blown-out highlights in PBR

Using physically based BRDFs only makes sense if your entire pipeline is built for physical units - the extreme range of values can't be displayed properly without some form of tone mapping. You didn'...
Accepted

### Anisotropic GGX BRDF implementation. How is it related to isotropic GGX BRDF?

After coming back to the problem now with a fresh pair of eyes, I have managed to find my mistake. Ad Question 1 Yes, the formula is correct. The problem is hidden in the tangent and bi-tangent . ...
• 121
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, ...
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### 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
Accepted

### Problem sampling uniformly envmap with GGX

How are you randomizing the samples you take? It looks to me like maybe the random values are the same across all pixels in the image, which would explain why you see 10 coherent bright spots when you ...
• 25.1k
Accepted

### What should I do when a new sampled direction is below a normal oriented hemisphere?

Disclaimer: I am assuming that you are implementing a classical Monte Carlo estimator. The Problem Discarding samples will change PDF of your sampling technique. You are cutting off part of the ...
• 1,464
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### How to approach implementing Cook-Torrence microfacet brdf?

Let's take a look at what' going on here. The Monte Carlo estimator is given by: $$\hat{I} = \sum_{i=1}^N\frac{f(X_i)}{p(X_i)}$$ The $f(x)$ (evaluation function) here can be writen as (simplified ...
• 1,002
1 vote
Accepted

### Why do I need to remove the positive charactaristic function for the pdf of the outgoing direction to integrate to 1 with GGX?

Looks like the boundary of the integration changes to positive m.n and so you drop the Heaviside fnc to reflect that. (Actually a sample for m.n<0 is not a valid sample, you ain't taking its value ...
• 302
1 vote

### Ray Tracing, why does the GGX make my rendering result darker and darker for each frame?

http://graphicrants.blogspot.com/2013/08/specular-brdf-reference.htm - here is reference with different geometry shading equations http://jcgt.org/published/0003/02/03/paper.pdf - paper explaining how ...
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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