How to Use GGX BRDF?

Development Rendering
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1

Hi There,
I have some questions.

I would like playing GGX shader in Unreal, but i have a problem.

I found many GGX hlsl code in BRDF. usf file, and call in custom node.

Here is it :

137381-ggx_node.jpg
137381-ggx_node.jpg1920×1048 304 KB

Code here :

// GGX / Trowbridge-Reitz
// [Walter et al. 2007, "Microfacet models for refraction through rough surfaces"]
float D_GGX( float Roughness, float NoH )
{
	float a = Roughness * Roughness;
	float a2 = a * a;
	float d = ( NoH * a2 - NoH ) * NoH + 1;	// 2 mad
	return a2 / ( PI*d*d );					// 4 mul, 1 rcp

I dont know how to use this node. Where to connect GGX custom node? (Specular? Metallic? Roughness?)

And what should be connected to the Roughness and NoH function?

I would like to use it as it works in Vray. It is possible?

2nd Question:

Is it possible to use Fresnel (Reflection) like in 3dsmax?

137384-fresnelref.jpg
137384-fresnelref.jpg903×1050 175 KB

Thanks in Advance, and sorry for my bad english.

Regards

Adam

2

UE4 already uses GGX. If you want to modify something, you should do it BRDF.usf and/or ShadingModels.usf files.

There is also fresnel material expression that you can use in the editor.