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DSandell

Adding hair to a rigged character

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Hello!

I have a rigged character that needs to be covered in hair. The character is fairly low poly and I'm using a Subdivsion Surface to make him smoother which seems to work fine, but when I add the hair (to the low poly model), the hair "grows" out of the low poly model, making it look pretty bad. I can't add hair to a Subdivsion Surface (it's greyed out) and I also cannot manually subdivide the model as that breaks the rig and the model completely, so I'm wondering if there's another way to solve this?

I guess I could remove the rig, subdivide the model, rig it again and then add the hair, but I hope there's an easier solution.

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Undocumented limitation of the subdivision surface in combination with the hair object. You need to use the Catmull-Clark mode, otherwise the hair will stick to the original polys.

 

Note: I just tested it and apparently the Catmull-Clark (Ngons) mode is fine now too (with R21). The other modes don't work though.

 

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  • I'm not quite sure I understand. When I select the subdivision surface and go to Simulate > Hair Objects > Add Hair, Add Hair is greyed out. If I use a hair object already linked to the base model (unsubdivided) parented to a subdivsion surface and try to link the guides to the subdivsion surface instead, it doesn't work and is instead still linked to the base model.

    Am I missing something?

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    You do not put the hair on the SDS. You put the hair on the basic polygon object. If you want to limit the hair to a polygon selection, this polygon selection needs to be on the basic polygon object too. While setting up the hair, you do not use the SDS at all. Ignore it.

     

    When Cinema is evaluating the SDS, it will automatically move the hairs according to the SDS (even if the SDS is deformed by Skin or a Displacement deformer) - that is, if the SDS is in the Catmull-Clark modes. If for some reason you absolutely need to use e.g. OpenSubdiv, you're out of luck - the hair will stay on the original polygons.

     

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  • Ok, I see. Thanks a ton for the explanation! I really appreciate you taking your time to help me. I am using the Catmull-Clark (ngons) mode. The problem I'm having is that I get some bald areas and some areas where it looks like the hair is clumping, even when I have clumping turned off. I assumed it had to do with the hair applying to the base model, because I thought the bald spots and clumps corresponded to the unsubdivided geometry. I now realize that doesn't seem to be the case at all.

     

    However, the problem is still there and I'm not quite sure what's causing it. There are some odd bald spots and clumping going on around the mouth. Earlier, I tried copying the model, removed it from the rig and manually subdivided it and then added hair, and for some reason, that model got perfectly even hair distribution.

    I've tried setting Root to "Polygon Area" under Guides > Roots in the Hair Object, instead of the default "Polygon Vertex", but that looks even worse. The copied model works fine with "Polygon Vertex", and all the default settings worked fine on this particular model before rigging it.

    I'm attaching an image of what it looks like. To the left is the rigged model in an SDS, to the right is the same model, but manually subdivided and without the rig.

     

    hairproblem2.thumb.jpg.d781f3f0012cc8f6d1e8c98c9a489136.jpg

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    1 hour ago, David Sandell said:

    Ok, I see. Thanks a ton for the explanation! I really appreciate you taking your time to help me. I am using the Catmull-Clark (ngons) mode. The problem I'm having is that I get some bald areas and some areas where it looks like the hair is clumping, even when I have clumping turned off. I assumed it had to do with the hair applying to the base model, because I thought the bald spots and clumps corresponded to the unsubdivided geometry. I now realize that doesn't seem to be the case at all.

     

    However, the problem is still there and I'm not quite sure what's causing it. There are some odd bald spots and clumping going on around the mouth. Earlier, I tried copying the model, removed it from the rig and manually subdivided it and then added hair, and for some reason, that model got perfectly even hair distribution.

    I've tried setting Root to "Polygon Area" under Guides > Roots in the Hair Object, instead of the default "Polygon Vertex", but that looks even worse. The copied model works fine with "Polygon Vertex", and all the default settings worked fine on this particular model before rigging it.

    I'm attaching an image of what it looks like. To the left is the rigged model in an SDS, to the right is the same model, but manually subdivided and without the rig.

     

    hairproblem2.thumb.jpg.d781f3f0012cc8f6d1e8c98c9a489136.jpg

     

    Whaaaa... yes, that looks VERY strange indeed. Would I assume correctly when I guess that the clumps on the lips coincide with the vertices of the mesh?

     

    Polygon Area is quite fine; the difference to Polygon Vertex is mostly seen in meshes where you have polys of very different size. In this case, Polygon Area equals out the density of the hair.

     

    The issue here doesn't look like a density problem though, and not like an SDS issue either. If I see it correctly, these clumps are growing longer and more irregular than the fur on e.g. the right cheek side (in the image right).

     

    Are you able to post a simplified mesh with these fur settings and the same hierarchy? I don't think I can solve that without seeing all the settings.

     

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  • Haha, glad to see I'm not the only one finding it strange.

    Yes, it looks like it matches perfectly with the vertices. It's what made me believe it had something to do with the SDS not working with fur initially. And yes, I think you're right about the density. It really looks like some clumps are longer while other spots are bald.

    I'm uploading a file in which the problem still persists, but the rig and most other things are deleted. Is this something you can take a look at? There are som Redshift objects and materials in the scene, I hope that doesn't cause a problem.

    ltk_lookdev_exp.c4d

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    51 minutes ago, David Sandell said:

    Haha, glad to see I'm not the only one finding it strange.

    Yes, it looks like it matches perfectly with the vertices. It's what made me believe it had something to do with the SDS not working with fur initially. And yes, I think you're right about the density. It really looks like some clumps are longer while other spots are bald.

    I'm uploading a file in which the problem still persists, but the rig and most other things are deleted. Is this something you can take a look at? There are som Redshift objects and materials in the scene, I hope that doesn't cause a problem.

    ltk_lookdev_exp.c4d 2.83 MB · 0 downloads

     

    Okay, dumb question but... did you realize there is hair inside the mouth?

     

    The whole thing is an interpolation issue. As you interpolate the hair from the 4 nearest guides, C4D takes the guides from BOTH sides of the mesh, simply because the guides on the backside are closest - regardless of the "distance on surface". It's a bug that was driving me crazy too.

     

    The only way to overcome the situation is to separate the hair into different parts which occupy only selected polys of the target mesh, and position the guides in a way so they don't interfere with each other.

     

    Here's the original fur (after removing Redshift stuff):

    ltk_lookdev_exp_01.thumb.jpg.ca92dc542a3d108035ca3edf2a30ead5.jpg

     

    Then I removed the guides from the inside:

    ltk_lookdev_exp_02.thumb.jpg.ec9d02c79447bc611c5572985136ebd5.jpg

     

    Better, but you can see that the hair on the inside is now growing the wrong way (to the outside, as all guides are now pointing there), and that the upper lip and lower lip guides are still interfering with each other, creating jagged mouth fur.

     

    Then I split the fur in an upper head part (incl. upper lip) and a lower head part (incl. lower lip). The inside now doesn't grow any fur, so I have reduced the fur count a bit:

    ltk_lookdev_exp_03.thumb.jpg.9bb64a172ce715c0532bf32a648cb399.jpg

     

    Looks too sparse now (I suspect that the dense fur above was actually inner fur growing to the outside, but it's rather late and you can check that yourself...), so I upped the hair count again for both halves.

    ltk_lookdev_exp_04.thumb.jpg.e9abf7bc8795add6ac89a84734ca1df4.jpg

     

    It's not perfect but that's as far as I'll go.

     

    ltk_lookdev_exp_0001.zip

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  • Wow! I had no idea the hair on the inside could ever cause a problem like this. Thanks a ton for your help, I'll look into this solution properly in the morning. This certainly sounds promising. Again, thanks for taking the time to help me.

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  • Alright, so now I've spent some time today trying to fix it, and it looks a lot better. However there are still some issues with the hair that I can't quite figure out.

    The first image here is my model in my scene, in which I've split the hair in two different groups as suggested. The second is using the mesh and hair object from the scene you posted above. In both cases, I've turned off Frizz, Kink and Clump in the hair material to get a better look at what's actually happening.

    As far as I can tell, there are no longer any hair guides on the inside, so I can't understand why it looks like this.

     

    hairproblem3.jpg

    hairproblem4.jpg

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