Root motion translation does not consider current rotation of object which will be applied root motion

[HitalloExiled]

Godot version

v3.4.2.stable.mono.official

System information

Windows 10, GLES3, RTX 3060

Issue description

In the current state, root motion always returns a transform with the delta of rotation and translation.

This works fine for most scenarios.

However, when an animation has both rotation and translation, things get complicated.

It is necessary to save the orientation at the beginning of the animation, apply the translation relative to the saved orientation while rotating the object using the root motion delta rotation.

Example:

using Godot;

class Player : KinematicBody
{
    private AnimationTree animationTree;
    Transform orientation;
    string state;
    Vector3 inputVelocity;

    public override void _Process(float delta)
    {
        Vector3 velocity;
        var rootMotion = animationTree.GetRootMotionTransform();

        if (state != "Turning")
        {
            orientation = GlobalTransform;
            velocity = inputVelocity;
            LookAt(inputVelocity, Vector3.Up);
        }
        else
        {
            velocity = orientation.basis.Xform(rootMotion.origin) / delta;

            var rotation = rootMotion;
            rotation.origin = Vector3.Zero;            
            GlobalTransform *= rotation;
        }

        this.MoveAndSlide(velocity);
    }
}

This can work on animations where translations end up with no delta translation and small/zero xfade.
Otherwise, if the animation ends with some amount of delta and/or xfade, things will break.

Digging on the issues i found this PR #29458 that tries to fix that.

Which unfortunately appears to have been abandoned.

Steps to reproduce

Create a root motion animation only with translantion.
Create a root motion animation with translantion an rotation.

create one state machine that travels from one state to another.

applies thee root motion to the transform

GlobalTransform *= rootMotion;

Minimal reproduction project

Example.zip

Presse W to walk and A or D to turn.

[TokageItLab]

It is fixed in 4.0 but still broken in 3.x. I misunderstood. The regression mentioned in #60774 does not exist in 3.x. This issue is for about another problem.

[LasseSchnepel]

Hi, in Godot4 Beta6 this still shows the same broken behaviour. Cannot confirm the fix.

[TokageItLab]

@LasseSchnepel Can you send MRP or video?

FYI, there is a DemoProject that shows that the rotation itself is gotten correctly. #29458 (comment)

[LasseSchnepel]

Hi Tokage, my assumption is that when I play the animation in the player (without the tree or with the root motion), the movement looks good. In your example project, the figure rotates and moves constantly forward. When used with root motion, your figure walks along a circle. I would expect that the figure moves as it would with the normal animation. (but with by the mesh at 0/0 and moving the outer node). This is also how root motion looks in all other engines afaik.

The rotating while moving forward animation is nothing one could easily animate in e.g. blender. In blender I want to walk my figure on a circle and then have Godot replicate that movement with root motion.

I attached an example project of mine (even though it is Godot.NET, is uses no .NET code, so should be usable without .NET):
rootmotion.zip
Press arrows up and left to move forward / rotate left.

[TokageItLab]

@LasseSchnepel Thanks for the project, that is a good reference.

After looking into it:
The root motion rotation is definitely usable. I think the problem you are implying is similar with #67125¹ rather than this issue. Here is the project I fixed.

fixed_rootmotion.zip

And I found several problems unrelated to this issue:

• delta in PhysicsProcess seems to be broken currently 🤔
• root motion scale is broken (I will send a fixing PR soon)
• the Left animation in your project is not at 90 degrees at the last keyframe (I don't mean to nitpick, but please be aware that the player will shift a bit after the rotation)

In any case, thanks for a good reference project. I don't see the need for any new implementation for root motion rotation for now, but I feel that the documentation needs to be a bit more detailed on how root motion is applied.

Footnotes

1. AnimationTree blend - initial rotation ignored when using root motion and changing the blend value in code. #67125 is a problem where they want to use the first keyframe as the initial value, but in your case they want to use the current player's orientation as the initial value ↩