Geometry nodes hair system is clipping under geo

[xalener]

Just cloning this thread from one I posted in BlenderArtists:

Hey everyone, I’m having issues with the new geo nodes system. The hair shown here has patches of baldness in the stubble (most visible under the chin) that is the result of the surface of the hair not matching the surface of the geometry. The geometry has a displacement modifier on it, and it does seem to be affecting the depth of the curve roots appropriately. If I turn the displacement up or down or on or off, the curves respond in kind, but they maintain their incorrect offset. I’m not expecting quick help as these are some pretty brand new features, but if we can find a lead on this issue it might illuminate future solutions for anyone who wants to do the same thing.

From Inside the geo

The stubble geonodes Stack                                And the geometry modifier stack

  

ok so here’s the quirk

I change anything about the head stack, the hair follows just fine. The areas that are broken stay conjsistently broken

so I’m certain the problem is specifically with the surface deform node in the stubble stack

ignore the shrinkwrap node, that was my first attempt at fixing the issue. It didn’t work

Upon further investigation, applying my base subdiv fixes the issue, which is so far below suboptimal it’s witnessing the central core slow down in real goddamn time. I would think at first that this means the geometry nodes don’t read the subdiv levels of the surface mesh, but the hair updates and changes when I change the subdiv levels! I’m truly stumped. This is a huge roadblock for me.

I’d greatly appreciate any help at all. I’ve got a copy of this thread in a few blender communities and so far I haven’t had much outreach. This has been a huge pain and it’s stopping me in my tracks. 

[Martin Bergwerf]

Hi @xalener ,

I haven’t used the new hair system yet; I will have toplay with it a bit first to understand how it’s working.

But, at a first glance, it looks strange/wrong to have the Surface Deform after the Shrinkwrap Hair.

[xalener]

The shrink-wrap is deactivated there. In fact, I’ve since removed it from the chain

[Martin Bergwerf]

Doesn’t Shrinkwrapping after the Surface Deform help?

[Adrian Bellworthy]

Like Spikey I haven’t yet played with the hair system,
I’m would assume though, it looks like it is probably to do with the modifier stack order.

[xalener]

Alright, so if I put a shrinkwrap *after* the surface deform, it pushes the ends of the curves above the surface. They’re still smeared and smushed and matted in the areas where there used to be holes, but for stubble and vellus, it’s not noticeable. It’s a very very bad solution to this problem. If anyone with any station happens across this thread, I certainly hope they can reach out and maybe we can figure out a way to make this just work ™️

But thank you Spikeyxxx for suggesting it!

[Martin Bergwerf]

It’s on my To Do List @xalener

[xalener]

Would you happen to know the cause, just to ease my burning curiosity or offer some closure?

[Martin Bergwerf]

Not yet; I’ll have to dive into the new hair system first 🙂 I’ll let you know as soon as I’ve figured it out.

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