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Blender Skin Modifier

Posted by JTippetts, 18 October 2012 · 1,421 views

blender 3d skin modifier animation modeling
There's a new official build of Blender up for download, and if you are one of those compulsive types like me who just has to play with new-feature builds on graphicall, then you already know that this release has some fun little goodies. Aside from the usual round of enhancements and tweaks to existing features, this release adds a neat little toy that has some serious potential as part of your character modeling pipeline: the Skin modifier.

This thing, quite frankly, is pretty neat. Essentially, it works like this:

You rough-in a shape using points and edges. (Just regular old geometry here.) No faces or anything, essentially you are just extruding and moving around a bunch of points to form a sort of skeleton. In fact, that is exactly what you are doing: building a skeleton. To this skeleton object, you can add a Skin modifier. What the Skin modifier does is, it encloses your skeleton mesh edges in a "shell" of 4-sided geometry. Almost like... well... a skin. You can select the vertices of your skeleton mesh and scale them (using CTRL-A) to increase or decrease the thickness of the skin mesh generated at that point.

The generated skin is a 4-sided mesh primitive, but you can add a Subdivision Surface modifier after it in the modifier stack to increase mesh detail. (You can't add a Multiresolution modifier, however, and sculpting on the Skin mesh is not supported. In order to do sculpting, you will need to Apply the Skin modifier.)

Now, this is kind of neat, and would certainly facilitate the quick creation of a rough base mesh preparatory to creating a detailed character model. Just rough-in the shape, convert to a mesh, add a multi-res modifier and sculpt away. But another neat feature of the Skin modifier is a button that you can click to convert the base skeleton wireframe to an actual Armature skeleton that can be posed to deform the generated mesh. With a single click, you can generate the character's full skeleton, already assigned to the mesh.

Nifty.

One bonus is that the generated mesh is relatively clean: decent edge loops, and at least passable quality at the joints. Branches get a bit complex, and you might need to do some manual cleanup of those vertices (or you might not; it really does an okay job). You could conceivably even use this technique to generate a low-poly base-mesh for re-topologizing an existing high-poly character. Just drag out points and scale to approximate the shape of the high-poly, apply the Skin modifer, then do some manual re-topo editing using the project to surface and possibly Shrinkwrap capabilities as needed.

I have yet to use it for any official character modeling, but this weekend I'm going to run a character through from start to finish and see how well it fits into the creation pipeline.




Reminds me of the technique behind spore mesh generation, sounds great.
I tried using this modifier for my latest model, worked like a charm =) However, I made my armature from scratch. Wanted less bones and a slightly different placement of them.
I'm finding it to be useful, yet glitchy. Sometimes, just a single fraction of a unit in scaling a vertex can mean the difference between smooth, continuous joint geometry and some kind of hideous, god-awful mess of hellish character. For example, I'm finding its greatest use to be in creating a basemesh for hands. I've always had a tough time with hands (evidence Goblinson Crusoe's current deformed, freakish mitts):

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The skin modifier is useful, as you can easily drag and tweak the base skeleton vertices as you wish, without having to do a whole bunch of mesh editing and tweaking:

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However, with just a little bit of scaling on a finger vert, you can obtain a hideous monstrosity of overlap, rather than the relatively clean (though imperfect) mesh above:

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For reference, a solid render:

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That is just not a good mesh. And that sort of ugliness happens quite often, especially in hands and feet. Of course, this issue is mentioned in the docs and online references for the modifier, especially for vertices that branch 3 or more times, and it can be worked around by careful scaling of the vertices. It is possible to do some pretty good hand, foot and claw base meshes this way, and certainly easier for me than grabbing and sculpting.
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