Questions tagged [microfacet]
The microfacet tag has no usage guidance.
24
questions
2
votes
1
answer
66
views
Lots of bad samples (below the hemisphere) when sampling the GGX VNDF
I've noticed that my implementation of GGX VNDF sampling produces quite a lot of bad samples (below the hemisphere). When such a sample occurs, I terminate the ray, leading to an immediate black pixel....
- 177
0
votes
1
answer
31
views
Microfacet-Based BRDFs general form
In Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs, author said that "we differentiate Equation (17)"
but how to get 2 from 1?
- 1
0
votes
1
answer
799
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
95
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 ...
- 177
1
vote
1
answer
76
views
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 ...
- 57
1
vote
0
answers
94
views
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
151
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
374
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 ...
- 23
3
votes
1
answer
208
views
Confusion of deriving the Jacobian of the reflection transformation in Walter et. al's 2007 paper
When deriving the Jacobian of the reflection transformation in Walter et. al's 2007 paper:
First we have a macrosurface BSDF which is:
$f_{s}(\mathbf{i}, \mathbf{o}, \mathbf{n})=\int\left|\frac{\...
- 31
2
votes
0
answers
111
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 ...
- 151
1
vote
0
answers
72
views
Implementing the derivation of the Smith Shadowing function for arbitrary distributions
I'm trying to implement the derivation of the masking function G_1 by Smith.
The appendix of Walter et al 1, Hammons presentation 2 and this research paper 3 talk in detail about it and I feel as I do ...
- 41
3
votes
1
answer
481
views
Implementing the example of Walter et al. (2007) paper
As the title suggests I'm trying to implement the last images of the "Microfacet Models for Refraction through Rough Surfaces" Paper by Walter et al. in OpenGL
I "think" (I had to ...
- 41
0
votes
1
answer
132
views
Microfacet BRDF artifacts
I've been trying to implement a microfacet specular BRDF based on the equations in Real Shading in UE4, but I'm getting weird ring-shaped artifacts in the highlights of rough surfaces:
Here's the ...
- 198
1
vote
0
answers
47
views
Mitsuba builds targets with scons but throws "undefined symbol" error when trying to render scene
I am trying to implement a custom add-on for Mitsuba, but when I use the Heightfield I have defined in another function call(WaveBrdfAccel) in main.cpp it compiles without any problems but when I try ...
- 11
3
votes
0
answers
266
views
Microfacet GGX not integrating as expected
I'm trying to complete a look-up table for an energy-conserving variation of microfacet GGX as implemented here: https://patapom.com/blog/BRDF/MSBRDFEnergyCompensation/
I have a (pretty standard) GGX ...
- 31