<p>According to E. Heitz (<a href="https://jcgt.org/published/0007/04/01/paper.pdf" rel="nofollow noreferrer">Sampling the GGX Distribution of Visible Normals</a>) it stands for &quot;ground glass unknown&quot;. I am not sure what the word unknown means though.</p>
<p>By the way, it is equivalent to <a href="https://pharr.org/matt/blog/images/average-irregularity-representation-of-a-rough-surface-for-ray-reflection.pdf" rel="nofollow noreferrer">Trowbridge-Reitz distribution</a>, introduced much earlier.</p>

CC BY-SA 4.0
2024-11-11T11:36:55.090Z
Is GGX leading to the use of Cook-Torrance BRDF?
bim
CC BY-SA 4.0
2023-06-19T19:14:24.993Z
2023-06-19T19:14:24.993Z
Aleš Koblížek
<p>Many render engines implement the microfacet model for rendering surfaces that are rough, metallic, and/or transparent, a concept first published in &quot;<a href="https://dl.acm.org/doi/10.1145/357290.357293" rel="nofollow noreferrer">A Reflectance Model for Computer Graphics</a>&quot; This model implies that surfaces comprise a large number of microfacets, each with a random slope. The slopes of all the microfacets on a surface can be categorized with a facet slope distribution function.</p>
<p>Some render engines like EEVEE and Cycles allow users to select such function (called a &quot;light scattering distribution function&quot; in Blender), and the default is <strong>GGX</strong>.</p>
<p><a href="https://i.sstatic.net/GwBkJ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/GwBkJ.png" alt="Blender nodes with GGX" /></a></p>
<p>GGX is presented in the paper &quot;<a href="https://dl.acm.org/doi/10.5555/2383847.2383874" rel="nofollow noreferrer">Microfacet Models for Refraction through Rough Surfaces</a>.&quot;</p>
<p>In this paper's introduction:</p>
<blockquote>
<p>We also introduce a new microfacet distribution, which we call GGX...</p>
</blockquote>
<p>...but they never explain <em>why</em> they call it GGX.</p>
<p>Perhaps it's mentioned somewhere else?</p>

<rendering><specular><microfacet><distribution>
What does GGX stand for?
NullPointerException
# What does GGX stand for?

(Asked by: username_0 on 2023-06-19)

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](https://dl.acm.org/doi/10.1145/357290.357293)" This model implies that surfaces comprise a large number of microfacets, each with a random slope. The slopes of all the microfacets on a surface can be categorized with a facet slope distribution function.

Some render engines like EEVEE and Cycles allow users to select such function (called a "light scattering distribution function" in Blender), and the default is **GGX**.

[![Blender nodes with GGX](https://i.sstatic.net/GwBkJ.png)](https://i.sstatic.net/GwBkJ.png)

GGX is presented in the paper "[Microfacet Models for Refraction through Rough Surfaces](https://dl.acm.org/doi/10.5555/2383847.2383874)."

In this paper's introduction:

> We also introduce a new microfacet distribution, which we call GGX...

...but they never explain *why* they call it GGX.

Perhaps it's mentioned somewhere else?

**Tags:** rendering, specular, microfacet, distribution


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## 1 answers

### Answer by username_1 on 2023-06-19. Score: 4 | Accepted answer

According to E. Heitz ([Sampling the GGX Distribution of Visible Normals](https://jcgt.org/published/0007/04/01/paper.pdf)) it stands for "ground glass unknown". I am not sure what the word unknown means though.

By the way, it is equivalent to [Trowbridge-Reitz distribution](https://pharr.org/matt/blog/images/average-irregularity-representation-of-a-rough-surface-for-ray-reflection.pdf), introduced much earlier.

> **Comments:**
> **username_2**: Is GGX leading to the use of Cook-Torrance BRDF?  

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