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Rubber arms in Spine vs 2dimensions.com

D@rkmoonXarX

In my current project we have a lot of rubber arms, which can be done okayish with the 8-bones on a path approach, but they still produce unwanted corners and bumps, which take some careful and time-consuming weighting or animated mesh deforms to take out.
I recently found a spine-like tool called nima on 2dimensions.com. And just for fun I tried a 2 bones setup with very gradual weighting to see if that could give me a rubber arm. I was surprised that it did so much better than Spine (see attachment). Am I doing something wrong in Spine? Why is the bend in Spine so ugly? Or does nima use a method like smooth subdivisions that Spine intentionally doesn't use?
Keep in mind that I intentionally went fast. I know that I can get better results in Spine if I put more time into it.
I constantly have to battle squiggly bumps in my weighted mesh animations, which nima doesn't seem to produce (however nima is still very beta and misses many other features). Is there any chance of getting smoother deforms like that in Spine? :think:

nimbling

You'll want to have a look at the Spine stretchyman project.

Basically, it uses IK to control two big bones to control a bezier curve, to control lots of little bones that warp your mesh attachment smoothly, giving you the fidelity you seek 🙂

Hm, I see you understand that already. What helped me was to just add more subdivisions to the mesh.

I do the monster lips and the pickle legs using the same thing:

D@rkmoonXarX

Thanks for your reply! Yeah the stretchy man example is awesome. And my results are decent if I do it like that too.
Still I was surprised that the tools produce such different results with almost identical looking meshes.

nimbling

Ha! I gave your image another look 🙂

I see what went wrong: You bound the mesh points to the two bones, rather than to the (I presume hidden?) batch of smaller bones.

Here, it should look more like this:

D@rkmoonXarX

Wow that's a lot of vertices. o.O
Thank you for sharing. I actually did do it the proper way for my 8 bone version. This was just an intentionally simplified test, because I know that this works in other 3D software with just 2 bones and very gradual weighting, but not in Spine. So I tried it in Nima and there it works with just two bones - but it doesn't look good in Spine. Sure it works with the path and the chain of many bones but it takes longer to set up for the amount of characters that we have. And for my game we really have to save up on vertices, so I still get some bumps on the resolution level I can afford.
I really appreciate that you took the time to make a screenshot. Maybe I am a bit too conservative with the vertices count :think:

Nate

Not sure why your deform is so bad. Here's a mesh with a similar number of vertices to yours (4 columns, ₂₀ verts high, relatively evenly distributed (even though this is probably not the best arrangement, see below)):

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You can try the arm project yourself here (with Spine 3.4.02+):
http://n4te.com/x/675-arm.zip

For the above I used some internal edges to get nice triangles, then used auto weights and clicked Smooth a number of times. I didn't do any manual weighting, took less than 5 minutes. 🙂 Try doing auto weights, rotate the bones the most you want them to bend, Smooth or otherwise adjust weights and vertices until it looks good, then put the bones back (it's nice to keep setup mode without a deform). You won't be able to use undo to rotate back since you want to keep your weight adjustments, so rotate the bones in animate mode. You can also select the bones and ctrl+c, rotate, adjust weights, then select bones and ctrl+v to paste the bone transforms back to what they were. Also you can use Edit Mesh mode with Deformed checked to move vertices around to improve where the mesh bends.

There will always be some volume loss at the joint with a tight bend. You can compensate for volume loss using deform keys, adding more vertices, or even adding a bone at the joint which you can scale to expand the vertices there. However, even without those workarounds, it shouldn't look as bad as your screenshots unless you've done something odd with the mesh or weights. You didn't show your triangles, so maybe they aren't nicely arranged, like the above?

You don't need so many vertices away from the joint, if you never deform those parts. You could move more vertices near the tight bend and get a better bend for the same vertex transform budget. Also you probably don't need so many internal vertices. I like to draw the bones, then do the weights. I put a vertex on each bone origin, then add more as needed. They don't necessarily have to go along the bone, but here is an example:
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I didn't spend any time trying to make the joint deform nicely, it could be improved by moving the vertices around and adjusting the weights.

D@rkmoonXarX

Thank you for your detailed reply. 🙂 Lots of helpful advice in there (some of which I am actually already using when I properly rig these arms).
I think the style I'm working with is just a pretty extreme case. Something about the arm being so narrow and not wanting sharp edges but round curves seems to be especially tricky.

I just didn't realize that programs could have their own different "flavor" in the way that bones bend meshes even when the geometry and weighting seems almost identical. I feel like nima is much better with very soft and gradually weighted setups (can it be that they somehow slightly rotate edges to compensate for dents?), while Spine can do sharp bends without completely crushing the volume (and the auto weighting is so much better 8) ).

Thanks again!

Nate

Spine uses linear blend skinning, which is very likely the same as what Nima uses since it is simple and fast. I very much doubt you are comparing apples to apples, the differences you see are likely differences with your mesh and/or weights. You didn't show your Spine triangles or the weights overlay, but from your deformation I can see your weights are not smooth (some vertices move less than others making the mesh edge wobbly). As I showed above, Spine deforms just fine with a similar setup. Spine can do graduated weights. We haven't done but weight painting yet, but auto weights and the Smooth button make it easy.

There are more sophisticated (and more computationally expensive) ways of binding meshes to vertices that we may implement in the future.

Auto weighting in Spine is quite fancy. 🙂 It's not just choosing bones that are nearest to vertices, it's a very sophisticated algorithm that respects the mesh topology.