Implement LookAtModifier3D

[TokageItLab]

Add a LookAtModifier3D. This modifier allows you to specify a forward axis and provides a two-axis Euler rotation to prevent roll the forward axis.

lkat001.mp4

• Follow up Implement a base class SkeletonModifier3D as refactoring for nodes that may modify Skeleton3D #87888

Features

Time-based interpolation

When the character changes the lock-on target, it will take a certain amount of time to rotate instead of immediately rotating its head. The time-based interpolation uses a tween, so several transition/easing types can be selected.

lkat002.mp4

Angle limitation

This option allows you to prevent the character's neck from rotating 360 degrees. The limitation means that half angle of the limit from the bone rest is the range of motion. Both symmetrical and non-symmetrical limitations are supported.

Also, when this option is enabled, time-based interpolation will provide rest-aware rotation, similar to AnimationTree blending. This means that in some cases the shortest path will not be selected to prevent bones from penetrating through the body. See also for-better-blending.

In addition, if the target moves outside of these limits, axis flipping may occur, where time-based interpolation is used.

lkat003.mp4

Non-linear damping

To prevent abrupt changes in angular velocity at the edge of the angular limit, the option is to start non-linear(b-spline) damping from the threshold value.

This helps simulate natural human motion.

lkat004.mp4

Origin setting

There are some cases where multiple bones need to always point in the same direction, such as the eyes.

For example, angle limitation may cause bone to flip outside their limits, which is not good because only one of the eyes will move significantly. Setting an arbitrary origin helps to solve this problem.

Origin from

For example, To solve the above problem, it is possible to set the head to origin for eyes. Or you can use BoneAttachment or parent-child Node3D.

Offset

The problem can be addressed by matching the origin by offset without any external node or bone as well.

lkat005.mp4

[TokageItLab]

Added:

• A configuration warning when the forward axis and rotation axis are parallel to the node (I think we should migrate to property warning later)
• Some comments to the code
• Some Notes to the document

[SaracenOne]

Discussed and tested during the Animation Meeting and everyone seems satisfied that it works and adds broadly useful functionality. 👍

It is also worth noting that it largely follows the spec put forward by the VRM consortium https://github.com/vrm-c/vrm-specification/blob/master/specification/VRMC_vrm-1.0/lookAt.md

[Repiteo]

Thanks!

[JekSun97]

@TokageItLab Thanks, I've been waiting for modifiers for skeletons for a long time!
I would like to know if there will be other modifiers in 4.4? If so, what will be their purpose?

[fire]

@JekSun97 Please review and contribute to the discussion here godotengine/godot-proposals#9885 (Needed Skeleton Modifiers)

[crei0]

I think there's a typo on the Documentation data doc/classes/LookAtModifier3D.xml, it's saying in some locations SkeletonModifier3D instead of the correct LookAtModifier3D

This is visible at the documentation page at https://docs.godotengine.org/en/latest/classes/class_lookatmodifier3d.html

Location 1:
The SkeletonModifier3D rotates a bone to look a target.
it should say
The LookAtModifier3D rotates a bone to look a target.

Location 2:
This SkeletonModifier3D rotates a bone to look a target. [...]
it should say
This LookAtModifier3D rotates a bone to look a target. [...]

And on Create a new node window on the tooltip and on the description section

PS: I've created an Issue for this at #99532