Artifacts on mesh-based hair with Blended Dual Lobe materials

[Kat]

Blender: 3.1.2, Daz Studio: 4.20.0.2, Diffeomorphic: 1.6.2.0969 (aea6662)

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Hello, I’ve found that in any scene in which there is any mesh-based hair asset that makes use of the Blended Dual Lobe material, when imported with the BSDF material method, the hair behaves incorrectly, as shown below.

The first image is taken from iray and the second is from cycles. Attached is the duf of this as well (Gen 8.1 figure and Toulouse hair with the shader applied to it.)

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Currently, the imported material makes use of the Hair BSDF node which does not function properly on meshes and a Blender Artists post from 2017 suggests using shaders meant for meshes.

[Alessandro Padovani]

If you look at the daz shader presets you see that blended dual lobe is for SBH, not for meshes. That’s why it is converted to the appropriate shader in blender. You shouldn’t have used BDL on toulouse to start with. Don’t know of any daz asset using BDL on a mesh, if it does it’s probably a bug.

That said we could check if BDL is used on a mesh and convert to principled in that case, that’s already supported. But it may be hard in blender to distinguish between a mesh hair and SBH ribbons. This is better left to the user.

So imho you should close and mark as invalid, if Thomas has nothing to add.

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[Kat]

The reason I put the BDL shader on toulouse was for demonstration to show the issue without using any rare assets, but there are at least a few hairs which use BDL on a mesh (these examples are all by the same creator): Lancy, Lurys, Keicy. That is how I first discovered this issue.

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As there are at least a few assets using this shader, I would not call it a bug for them to be doing so, but I do agree that this is a use case which should not happen.

[Alessandro Padovani]

Unfortunately it is not uncommon that some PAs don’t understand the daz shaders and/or other features of daz studio, thus publishing “buggy“ assets. If you look at the parameters in the BDL it is absolutely clear it is meant for strands, not for geometry.

Then again Thomas may want to try to fix this using the principled shader as explained above. Personally I wouldn’t.

edit. note. But the figure pages you linked state it’s dforce hair, and they also look as strands from the images. So is it not true and they use mesh hair instead ? Or may it be you just didn’t convert the polylines with the “make hair“ tool ? That is, dforce hairs need to be converted to work in blender.

https://diffeomorphic.blogspot.com/p/hair-section-version-16.html

[Kat]

Just looking at the Lancy hair, the asset provides two versions. There is a sheet hair which does not support dForce and an alternate stand (or polyline, I don’t know how to tell for certain) version which does. Both ultimately still use BDL shaders.

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Since this is clearly a case which is not supposed to work, and as I imagine Thomas is not interested in figuring out how to deal with it, I will close this issue.

[Kat]

This is a use case which is not supposed to work anyways.