Expected Substrate-Hair-BSDF to have double-layer highlights and anisotropic properties

Development Rendering
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A single layer of highlights often does not meet the needs in film and television production, For example, a layer of hair material highlights, a layer of water moistened highlights，while double-layer highlights like Substrate Slab are good.

We also need anisotropy parameters to control the direction of hair highlights. We found that the Tangent attribute in Substrate-Hair-BSDF already controls the rotation angle, but without anisotropy, Tangent would not be effective.

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2

Hi there,

I spoke with the owners of the Substrate feature, and they have said that it is unlikely we will add anisotropy parameters to art-direct hair highlights. However, we already have a large set of features available for use in Substrate, which could help you achieve your look. Could you share an example of what look you are going for with your hair? That way, we can give you some alternate suggestions.

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The key is the double-layer highlight, as shown in the attached image, which clearly shows two layers of highlights with different roughness. When used in combination, it could look more dimensional material.

As for the fact that anisotropy is not very important, I just don’t understand how the Tangent parameter would function without anisotropy parameter.

I used a substrate rotation-to-tangent and nothing happened, so I guess if there is an anisotropic parameter and the angle is adjusted with the substrate rotation-to-tangent, the highlight position should shift. But this doesn’t matter.

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4

Hello,

The hair shading is achieve using what is shown in that presentation with parameterization from slice 43 specifically:

  • The R lob can be controlled using the Specular and roughness attribute. It is white specular
  • The TT and TRT lobes are deduced form those parameters, with transmittance related to BaseColor also. TRT is the second lobe you are talking about and it is there, its longitudinal shift and roughness cannot be authored specifically. I do not think we have any plan to expose that in the short term, at least since the GBuffer is already full. I believe you will have to update the current input to what you need and modifying the code as you see fit.
  • Multiple scattering is approximated using the BaseColor and Scatter input to control the amount of multiple scattering approximation.

The tangent typically comes from the mesh or groom data, or a texture. Just make sure you select the correct space to specify it on the root node using the Tangent Space Normal property. You can specify 3d vector directly per pixel, there is no need for an anisotropy parameter. You will need to rotate that vector in tangent space first before moving it into world space if you want to.

I hope this helps.

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The different lobes:

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6

Thanks. That’s helpful. We’ll give a try.

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