Visualize Fresnel?

Maximum-Dev

Hello,

How can I visualize Fresnel in UE4? the Specular visualizer doesn't show the Fresnel/specular gain on extreme angles.

Thanks in advance.

Obscura

You can make a blendable postprocess that shows the fresnel, but I'm not sure if its the same fallof that is used in the shading.

To do this, make a new material, set material domain to post process.. Now place "fresnel" node, and just plog that into the emissive slot. Now add this blendable to the array of blendables in the post process volume, and you have a pp that shows the fresnel.

Maximum-Dev

Obscura said:

You can make a blendable postprocess that shows the fresnel, but I'm not sure if its the same fallof that is used in the shading.

To do this, make a new material, set material domain to post process.. Now place "fresnel" node, and just plog that into the emissive slot. Now add this blendable to the array of blendables in the post process volume, and you have a pp that shows the fresnel.

Thanks. But that's not related to the material Fresnel?
What I'm trying to do is to make some adjustments to the material Fresnel i.e Multiplying AO by Fresnel in for a brick material. But there doesn't seem to be any control regarding that?

Obscura

Maximum-Dev said:

Obscura said:

You can make a blendable postprocess that shows the fresnel, but I'm not sure if its the same fallof that is used in the shading.

To do this, make a new material, set material domain to post process.. Now place "fresnel" node, and just plog that into the emissive slot. Now add this blendable to the array of blendables in the post process volume, and you have a pp that shows the fresnel.

Thanks. But that's not related to the material Fresnel?
What I'm trying to do is to make some adjustments to the material Fresnel i.e Multiplying AO by Fresnel in for a brick material. But there doesn't seem to be any control regarding that?

Yes, thats what I said, this will only show you the fresnel on everything...

What you could do however, is to multiply your ao map by inverted fresnel, and then multiply that by 0.5 (default specular value) and plug it into the specular slot. This would make your material have less specular reflections on the fresnel angles, based on your ao map.



You can use the specular slot to control the intensity of the specular reflections. 
When its set to 0.5, that equals to the non-metal reflectance - 0.04 like when you plug nothing into the metallic and specular slot. That 0.5 is also its default value.

Daedalus51

I guess you want to visualize the Schlicks Fresnel Term that happens inside Unreals BRDF Calculation, but as far as I am aware of it, there is no way to visualize it.

The fresnel node in the material editor is just a simple dot product and sadly, by no means close to the Schlick term as modeled in the base BRDF.

There is probably a way to recreate Schlick Fresnel inside the material Editor to just output a grayscale image you can render on objects, but I am not sure if this is possible without custom lighting.

https://en.wikipedia.org/wiki/Schlick's_approximation
https://seblagarde.wordpress.com/tag/fresnel-schlick/

ActionDawg

To make the final term, based on Schlick's:

Get your specular value (if you have one) and multiply it by 0.08. Otherwise use 0.04. Call this x. Then in the material editor do:

x + (1-x)(1-fresnelnode)^5

This will compute almost exactly what UE4 uses for fresnel. They actually do not use a standard Schlick's, but rather a faster gaussian approximation. It's not exactly expensive though so go ahead and just implement the above.

If you need this to support metalness there's an extra step.