MeshPhysicalMaterial: clearcoat should not use underlying normal map

[RenateOnVizoo3d]

I have recognized that the PhyscialMaterialShader is taking the perturbed normal of the material into consideration.
Seeing how the effect is implemented elsewhere (e.g. in Blender using the Principled BSDF shader node), I would expect the clearcoat to behave like a "flat additional coating" on top of the material and not being perturbed by the underlying normal map. Thus as a change request, I would suggest to conserve the "original" normal which should be fed into the calculation of the clearcoat reflection.

In order to achieve this getLightProbeIndirectRadiance needs to distinguish between specular and clearcoat reflection mapping; see Pseudocode:

vec3 getLightProbeIndirectRadiance( const in GeometricContext geometry, const in float blinnShininessExponent, const in int maxMIPLevel ) {

      vec3 reflectVec;
      if ( specular_reflections ) {
            reflectVec = reflect( -geometry.viewDir, geometry.normal );
       } 
      else {      // clearcoat reflections
      reflectVec = reflect( -geometry.viewDir, geometry.clearCoatNormal );
      }
[...]
}

Alternativley passing the respective normals via the the function parameters (or adding the .originalNormal to the GeometricContext structure) could help too,

Cheers,
Renate

img attachment: glossy leather with clearcoat on top

Three.js version

• Dev
• r88
• ...

Browser

• All of them
• Chrome
• Firefox
• Internet Explorer

OS

• All of them
• Windows
• macOS

• Linux
• Android
• iOS

Hardware Requirements (graphics card, VR Device, ...)

[WestLangley]

Can you hack a live example as a proof of concept?

[RenateOnVizoo3d]

In the package attached you'll find the modified three.js file as well as some notes, what I did to achieve the effect. For SURE, there are better ways to do this.
As I am new to this: pls let me know if other files/ implementation is expected.

[-> removed zip file and replaced with online demo on Jan 18]

[WestLangley]

If you could include a live example in the zip file that would be helpful...

If we were to implement this, I expect we would allow the clearCoat to have a separate normal map, that way, clearCoat surface scratches can be modeled. It is also a more general solution.

[RenateOnVizoo3d]

Here is our test environment. Please unzip and run index.html (ideally in Firefox as we have not tested it elsewhere). Then browse (top left corner) for /materials/Green Leather/Green Leather.xtex
Let me know if this works.

[-> removed zip file and replaced with online demo on Jan 18]

Totally agree. An (optional) separate clearcoat normal would be the most meaningful solution. Thus clearcoat would be specified by intensity, roughness and normal.

[WestLangley]

I think your demo is going to have to show a side-by-side comparison of two spheres to be able to see the subtlety you are trying to implement.

Thus clearcoat would be specified by intensity, roughness and normalMap.

... and normalScale.

[RenateOnVizoo3d]

Please see the original version of the webGl_testenvironment attached.
[-> removed zip file and replaced with online demo on Jan 18]

You should see the difference compared to the implementation in my last post when playing with normal, clearcoat / clearcoat roughness and environment intensity. here (webGl_testenvironment - originalClearCoatBehaviour.zip) the clearcoat gets perturbed by the normals and here (webGl_testenvironment.zip) the clearcoat stays as a flat reflection layer.

See more explanation on the clearcoat behaviour here:
https://docs.blender.org/manual/ru/dev/render/cycles/nodes/types/shaders/principled.html

[WestLangley]

Your demos throw console errors for me. Sorry, I am not able to invest the time to debug this.

I am still interested in your suggestion, however.

[mrdoob]

/cc @bhouston

[bhouston]

Unreal Engine 4 does this:

https://docs.unrealengine.com/latest/INT/Engine/Rendering/Materials/HowTo/ClearCoatDualNormal/

I've wanted this as well.

Basically the main way to do this is to add a second normal map and have it used for either the top layer or the bottom layer. I would prefer to have the second normal map be used for the surface because then we can call it clearCoatNormalMap and it is part of the clear coat top layer.

If it isn't specified, then we would use the underlying normalMap for both? Or we could allow for a scalar parameter, clearCoatNormalWeight, that would scale between the clearCoatNormalMap and the underlying normalMap - normally it would be 0 and thus favor the underlying normalMap/bumpMap, but if you set it to 1 it would use the clearCoatNormalMap completely or it would be perfectly smooth if the clearCoatNormalMap isn't set.

Does that logic work?

[WestLangley]

It is probably sufficient to keep it simple and just to add two properties:

material.clearCoatNormalMap
material.clearCoatNormalScale

If clearCoatNormalMap is null, the clear coat uses no normal map.

[bhouston]

It is probably sufficient to keep it simple and just to add two properties:

Sure, I am fine with your suggestion. Just to be clear, this is for the top layer normal and not the bottom layer as it is with UE4? I think that is the more logical choice. clearCoatNormalMAp == null leads to a smooth surface for clearcoat but normal/bump affect the underlying layer.

[WestLangley]

@bhouston Correct.

[RenateOnVizoo3d]

@WestLangley First, apologies for the example throwing errors. This should not have happened.

@bhouston I just wanted to confirm from our side that a clearCoatNormalMap == null should lead to a completely smooth, unperturbed clear coat layer. As if the materials has an additional transparent painting.
To keep it simple I would use the second normal map only for the clearcoat (top) layer. The bottom layer should not be affected.

For a comprehensive implementation a
material.clearCoatNormalMap
material.clearCoatNormalScale
would be needed to control the normals of the clearcoat. Moreover the intensity and roughness of this layer would be tweaked by:
material.clearCoat [0 = off, 1 = on]
material.clearCoatRoughness [0 = smooth, 1 = rough]

[RenateOnVizoo3d]

@WestLangley

Your demos throw console errors for me. Sorry, I am not able to invest the time to debug this.

Did you try in Mozilla Firefox? The demo is not running in any other browser yet