IK Post Processing pass using `SkeletonModifier`

[GuilhermeGSousa]

Depending on the MMSynchronizer being used, capsule to skeleton synchronization may cause foot sliding. This requires a SkeletonModifier to use IK to lock feet in place.

[GeorgeS2019]

Godot 4.4 built in IK https://github.com/GuilhermeGSousa/godot-motion-matching/discussions/29

[fire]

What are the expected inputs and outputs for the ik?

So I can modify my many bone ik to use this.

[GuilhermeGSousa]

I haven't given this much thought yet, but for feet IK we might only need the feet's bone names.

This isn't implemented yet, but we might want to run motion matching queries against world points, to do stuff like touching a wall when moving past one, touching a surface when vaulting, etc. In that case, the skeleton modifier would also need both the bones affected by IK, and the world position they must reach.

Depending on the synchronization method used to sync character capsule and character skeleton, we might also want to do some stride warping. I've used this method in Unreal, it works pretty well, it allows us to clamp the skeleton to the player capsule, then warp the leg stride of the animation to match the speed of the capsule. In that case we'd need

• The character speed and character thigh bone, so we can estimate the correct stride distance.
• An influence coeficient from 0 to 1. Depending on how much we rely on root motion to move around we might not need the full effect of stride warping.

[GuilhermeGSousa]

If you want to see for yourself what these MMSynchronizer actually do, if you play the demo you'll notice that the player capsule and skeleton are two independent nodes with no parenting relationship. Without a sychronizer the only thing that allows the skeleton to follow the capsule is animation selection from motion matching. This can look good, but its often not enough and depending on the cases we need a way of sychronizing player capsule and skeleton. Depending on the approach you get different pros and cons:

• Move the capsule to the skeleton's position: no foot sliding, but the character is harder to control for a player. At Naughty Dog they use this approach for AI characters
• Move the skeleton to the capsule's position: you get perfect controllability, but with foot sliding. This is the case that needs IK solutions the most