Questions tagged [ggx]
The ggx tag has no usage guidance.
14
questions
7
votes
1
answer
2k
views
Anisotropic GGX BRDF implementation. How is it related to isotropic GGX BRDF?
Introduction
I am implementing anisotropic GGX BRDF and have encountered strange behaviour of my implementation. I thought that if I compare the microfacet distribution function I have with the one ...
- 101
6
votes
1
answer
641
views
Dealing with blown-out highlights in PBR
I've been writing some custom shaders based around Unity's Standard BRDF, which is uses GGX distribution term and Smith visibility term. It looks great at either end of the smoothness scale (1 and 2 ...
- 2,302
5
votes
1
answer
95
views
What should I do when a new sampled direction is below a normal oriented hemisphere?
I generate random directions from the pdf of D term in GGX BRDF. On the picture, white dots are new directions and the cross is the light direction, with roughness = 1. What should I do with the ...
5
votes
1
answer
586
views
Can microfacet BRDF (including ggx) represent perfect mirror?
Perfect mirror's brdf is simple,
$F\frac{\delta(\omega_i-\omega_r)}{|\cos(\theta_r)|}$
as in http://www.pbr-book.org/3ed-2018/Reflection_Models/Specular_Reflection_and_Transmission.html
As shown in ...
- 51
4
votes
0
answers
1k
views
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 ...
- 2,413
3
votes
0
answers
271
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 ...
- 117
3
votes
0
answers
123
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 ...
- 117
2
votes
0
answers
92
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 ...
- 51
1
vote
1
answer
1k
views
Can't understand the Importance sampling GGX
I've read many articles relating to importance sampling of GGX. However, I still feel confused.
The formula of GGX is :
And many article says we should use this formula to sample:
In the formula, ...
- 177
1
vote
0
answers
50
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 (...
- 11
1
vote
0
answers
581
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:
...
- 177
0
votes
1
answer
51
views
Problem sampling uniformly envmap with GGX
I have made a program that samples uniformly an environment map and computes the lighting using the GGX BRDF.
I have made a small example that reproduces the issue I'm having. You can check it out ...
- 117
0
votes
2
answers
276
views
Ray Tracing, why does the GGX make my rendering result darker and darker for each frame?
I am trying to add GGX and PBR textures to my GPU ray tracer. The result is very strange, it's getting darker for each frame.
...
- 131
0
votes
0
answers
57
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.
...
- 131