Implement SpringBoneSimulator3D to wiggle chained bones

[TokageItLab]

• Closes Enable jiggly bone chains that work with colliders by using existing work in Godot-VRM godot-proposals#5605
• Closes Add 3D spring bone support for character hair physics simulation godot-proposals#8374
• Supersedes/Closes Add SpringBone3D node #84604
• Include Disallow changing element size of the static array property on the Editor #101313 Add const hint to array property to disallow changing element size #101422

spring_bone_demo.mp4

Model: アリシア・ソリッド / CC by DWANGO Co., Ltd.

This SkeletonModifier3D is ported from https://github.com/V-Sekai/godot-vrm and some additional features are implemented.

The movement logic is published by VRM Consortium (https://vrm.dev/en/univrm/springbone/univrm_secondary/) under the MIT license, SpringBoneSimulator3D reproduces that behavior.

This modifier behaves differently from PhysicalBoneSimulator3D as it attempts to return the original pose after modification.

SpringBoneSimulator3D

It has the bone chain settings as an array. Setting the root bone and end bone generates a static array in the joints group with reference to the joints in between.

After set root bone and end bone:

For simplified setup, you can use curves. When you edit a curve, the values scaled depending on it are cached in the static array.

With Option individual_config, detailed settings can also be made for each joint.

Parameters

RotationAxis

If sets a specific axis, it acts like a hinge joint.

hinge.mp4

Also, setting this up with aligned axes in a radial shape also helps to prevent collapse of the skirt.

Entend end bone

As explained some times in #32393 and #57038, glTF does not have information about the length of the bones, so even if the end bones have tail in DCC, it will be missing on export.

This option would allow the tail to be added to the end bone without having to add a leaf bone and export it.

Physical Parameters

Radius

It is used for collisions with SpringBoneCollision3D, described below.

Stiffness

The greater the value, the faster it recovers to its initial pose.

Drag

The greater the value, the more suppressed the wiggling.

Gravity

Direction and amount can be set.

SpringBoneCollision3D

Collision for SpringBoneSimulator3D that is processed in the SkeletonModifier3D process independently of PhysicsServer3D. It must be a child of SpringBoneSimulator3D in order to manage the process order. For each bone chain, depending on the SpringBoneSimulator3D.are_all_child_collisions_enabled option, either an excluded list or an allowed list is available.

SpringBoneCollisionPlane3D

A infinite plane collision. It is an infinite size XZ plane, and the +Y direction is treated as normal.

SpringBoneCollisionSphere3D

A sphere shape collision.

SpringBoneCollisionCupsule3D

A capsule shape collision.

The capsule and sphere collision have an inside option as the function to trap the joint.

[fire]

We had some debate about whitelisting vs blacklisting the collisions.

We mentioned that VRM standard uses whitelisting.

@lyuma had concerns that inverting the listing would suggest that the less performant option is easier to do.

Tokage is ok with either but proposed blacklisting.

[TokageItLab]

If we are concerned about performance, this is not much of a basis for concern, since we need to be careful when using either list.

The most serious problem is that without allow list, you cannot control the order in which collisions are handled on a per-bone chain basis, which could break strict compatibility with VRM. So support for permission lists is a must.

collisions.mp4

However, I believe it is necessary for quality of life, because when using exclusion lists, the user's operation steps when creating a mockup are cut in half or less.

For example, the following case:

1. There are 4 bone chains, 5 normal collisions, and 1 inside collider.
2. Apply the 5 normal collisions to all bone chains.
3. I want to apply the inside collider to only one bone chain. However, I need to exclude the inside collider from the other 3 bone chains.

In this case, the allow list would require 4*5+1=21 steps, whereas the exclude list would only require 3*1=3 steps.

However, in the case where 5 normal collisions are not applied to all bone chains (so if step 2 is not needed), the allow list requires fewer steps.

So it is a matter of which direction to go in to the destination state, and I thought both should be supported. For now, it resets when the allow/exclude list is switched, but I think we can send follow up PR with an option to invert the list in the future if there are demands.

[AThousandShips]

Looks good otherwise

[TokageItLab]

Squash to include #101422.

[akien-mga]

Only did a cursory review, seems fairly self-contained and the code looks clean.

[akien-mga]

@Mickeon I foresee you might want to do a follow-up PR to improve the flow of the docs added in this PR (all SpringBone* classes).

[lyuma]

Overall very nice. We should merge it so users can start playing with it. I haven't verified the math entirely but from reading the code it looks familiar / similar to the GDScript godot vrm implementation so I am fairly confident it should work.

The api covers both advanced and simple uses, in a way that adds minimal implementation complexity. I think it should be very nice

small docs question: does height in capsule collision work the same way as height in CollisionShapeCapsule? (Is it inner or outer height including top/bottom) we can fix docs after merge.

[TokageItLab]

small docs question: does height in capsule collision work the same way as height in CollisionShapeCapsule? (Is it inner or outer height including top/bottom) we can fix docs after merge.

Yes, I remember there was a recent change in the height to include the hemisphere in CollisionShapeCapsule, so I adapted the behavior to that.

[akien-mga]

Thanks!

[shiouhuamien]

Sorry, I found 2 issues while testing the 4.4 beta. I don't know if I should report them here. I'm sorry if I offended you.

1.Individual Config are only valid in the editor and will become invalid after running and all settings will be cleared.

2. Collision is only valid in the editor, not during runtime
It turns out that the collision setting is a blacklist. I made a mistake myself. Sorry.

[TokageItLab]

@shiouhuamien It sounds like the Animation and Skeleton processes do not match.

These must be matched. After you check them, if you still have problems, send the issue on the https://github.com/godotengine/godot/issues with the minimal reproduction project file.

[fire]

Maybe matching can be turned into an editor node warning

[TokageItLab]

@shiouhuamien I have confirmed a problem with the indivisual config and sent a fix. Please check it if possible: #101729