Unity's Smoothness HDRP to UE5 Roughness (RMAO)

armagon · Jan 10 2025

Hello! I'm trying to convert a Unity project to Unreal and stumbled upon assets that are using Smoothness maps in Unity HDRP. It seems that they are just inverted Roughness maps, but I wanted to make sure by asking the pros.

armagon · Jan 10 2025

This seems to be my answer: https://github.com/Unity-Technologies/Graphics/blob/master/Packages/com.unity.render-pipelines.core/ShaderLibrary/CommonMaterial.hlsl#L45

Unity converts Smoothness to roughness inside the shader and defines it as:

real PerceptualSmoothnessToRoughness(real perceptualSmoothness)
{
return (1.0 - perceptualSmoothness) * (1.0 - perceptualSmoothness);
}

Eric Chadwick · Jan 10 2025

Yes, smoothness is the inverse. However it could be that the Unity materials were using Specular Glossiness workflow, which requires a bit more work to convert properly to Metallic Roughness. @EarthQuake has a great walkthrough of that process here: https://marmoset.co/posts/pbr-texture-conversion/

Sage · Jan 10 2025

MetallicSmoothness maps have the roughness maps inverted as mentioned. The packing is a little different to Unreal.

the alpha channel has Smoothness (inverted Roughness map) information
The metalness are the other channels. Usually it's the same information in the R, G and B.

The normal map is openGL and the Green channel has to be flipped for it to look correct in Unreal.

armagon · Jan 11 2025

Unreal is DirectX?

Sage · Jan 12 2025

Yes. Unreal is Direct X by default. You can use the Open GL normals in Unreal, but inside of Unreal there is a check mark that flips the green channel.

Unity's Smoothness HDRP to UE5 Roughness (RMAO)

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