Ideal number of body parts to avoid joint deformation?

Abelius

Hi there people,

I've been meshing and rigging a human character, experimenting with two ways of approaching this task:

Same image for upper and lower leg.
Separate images for upper and lower leg.

In case 1 I have the problem that is mentioned here:
Weights and Bones workflow issues

And as it's suggested there, it would seem that I'd need to either make extremely complex meshes or move the affected vertices every time I bend an arm or a leg.

In case 2 I've been encountering other problems, but I think it's better not to describe them yet.

So, my main question here is...: in principle, what is better for a natural joint bending? Using different images for each body part? Or using a bigger image that encompass a whole limb?

Thank you!

Abelius

Nate

With separate images you'll need to cover the joints, either in the 2 images (like spineboy) or by using a 3rd image/mesh. The latter probably needs adjustment when the joint bends, so may not be better than using a single mesh and adjusting vertices at the joint to restore volume when it bends. You could use a 3rd bone with a single mesh, where you scale the 3rd bone to increase the volume at the joint. That may be easier than manually moving mesh vertices. The mesh topology, number of vertices at the joint, and the weights can make a big difference, increasing the amount of bending before volume loss. FWIW, here's a single mesh arm:
http://n4te.com/x/675-arm.zip
This was done in just a couple minutes by creating some internal edges to get nice triangles, then using auto weights and clicking Smooth a few times. It may be possible to improve further with manual weighting, but it can bend ₄₅ degrees before volume loss at the joint becomes noticeable.

Abelius

Then I think I'll try with single images and the 'control bone' approach. As you say that's definitely better than moving the verts manually.

About the example, I won't lie to you: I don't like it. 😃 It's still deforming a lot at 90º bending. But I suppose that's something that can only be averted with around 300 verts covering the whole joint. Nevertheless, I'll try that as well and see if it eats too much processing power or not.

The other way with multiple images wasn't doing much to improve my problem as you correctly have guessed.

Thank you Nate! :yes:

Oh! May I suggest a feature request related to this?

How about adding the possibility of binding a bone to another? I mean, that if you bend the master bone then the 'slave' bone bends in the opposite direction, according to a configurable influence value.

Thanks to that I could bend the lower leg and then the joint volume would be automatically increased to compensate. Wouldn't that be nifty? :-)

Nate

It's true sharp bends can lose a lot of volume. In the future we hope to provide alternate algorithms for attaching meshes to bones that don't have this issue (but will be computationally more expensive).

You can bind one bone to another using a transform constraint. It only allows same properties, eg rotation to rotation, not rotation to scale. You can set a negative rotate mix to have a bone rotate in the opposite direction.

Note that rotate mix > -100 and < 100 and != 0 can cause snapping if the target bone rotates near the opposite direction from the constrained bone, because it mixes the shortest way around. Spin the target bone 360 degrees and you'll see what I mean, the constrained bone will jump to the other side.

Abelius

Nate wrote
You can bind one bone to another using a transform constraint. It only allows same properties, eg rotation to rotation, not rotation to scale. You can set a negative rotate mix to have a bone rotate in the opposite direction.

Mmm... ok. I'll try to play with that. Didn't notice that option before... so much to cover. |(

Nevertheless, since my last post I've come to use two control bones: one for the upper limb and another one for the lower. It's working well I think, but I need more time to test it along with your suggestion. I'll report my findings for some other people's benefits. :p

Thank you again!