How to Use GGX BRDF?

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 :

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?

Thanks in Advance, and sorry for my bad english.



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.