Skinning and Bones Help?
polycounter lvl 7
I haven't done much animation work in the past and I'm having trouble with it. I have to constantly change my topology as I work to make the mesh animate properly, which includes lengthening arms and legs and things, my problem is basically every time I have to reposition a bone, I have to completely rebuild my Skin and all the weights on it.
How do you edit bones and things without messing up your Skin modifiers? I need to move this bone around but I can't do it in any way that wont result in me needing to remake my skin modifier again and again.
How do you edit bones and things without messing up your Skin modifiers? I need to move this bone around but I can't do it in any way that wont result in me needing to remake my skin modifier again and again.
Replies
Normally you're topology and portions should be pretty set before animating and there shouldn't be too much back and forth, thats not to say it isn't flexible and can't be changed but its not really open to constant broad sweeping changes.
Some things you can do when the topology changes.
When you have to destroy skin to make your changes, copy your mesh, delete skin, make your changes then "skin wrap" your newly changed mesh to your old which is still bound to the skeleton, convert it to skin and do a little clean up.
Save the animation, clear the animation, put the skeleton back in the bind pose, turn off "always deform" in the skin modifier, edit the bones using bone tools, turn on "always deform" in the skin modifier and do a little clean up, load the animation onto the skeleton and pray that it handles the transition well. Some rigs like CAT, biped and PuppetShop do it well, custom bone rigs not so much...
Sometimes you can use the scale of the bones to tweak proportions on a skinned model. It helps to reset the scale and transform (hierarchy tab > reset scale/transform) after you're done editing the bones that way they're zero'ed back out.
Hope that helps. I tried to be a little generic in case you're working in Maya, the theory is almost the same but you use transfer maps to transfer the skin weights.
Another option, although sometimes imperfect, is the SkinUtilities tool. Its under the Tools tab, but is usually not visible by default. It allows you to extract the skin data onto a special mesh that can then be used later to re-import the skin data onto another mesh. It also does some blending stuff, so if the mesh has changed, it can still figure out how to skin the changes. This tool can be a bit inaccurate and slightly buggy, but solid overall.
In the Skin Modifier you can also save the weighting, envelopes and custom vertex weights using Advanced Parameters, Save/Load. If you've changed the topology you will want to uncheck "Load Vertices by Index" when you're loading it back onto a mesh that has changed.
The load/save in the skin modifier is quite a bit more stable but it does lack the "threshold" feature which can be handy. Normally the Threshold in skin wrap modifier gives you more flexibility with its deformation engine settings: Fall off Distance, face limit, Bliend to base mesh bla bla bla it also and allows you to visually tweak the settings and see how the mesh deforms instead of just giving one setting and no visual feedback until after its been loaded.