Root motion isn't applied to non-humanoid animations via Animator probably due to missing Avatar

[XtroTheArctic]

Describe the bug 💬

(See the EDITs below, first)

In this issue (#869) and in this PR (#870) I did set the Root Motion of the created Animator to true but it turns out, Animator requires an avatar to be able to apply root motion to non-humanoid models.

So, the avatar creation for non-humanoids must be added to UnityGLTF importer, making it consistent with FBX importer and compatible with Mecanim Animator.

As seen in this screenshot, the horse moves within its local space without moving the object itself (as shown at the location of Unity's Transform Tool Gizmo):

As seen here, Unity's FBX importer creates an avatar for non-humanoid model so that Animator can apply root motion.

EDIT 1

After working on fixing the non-humanoid avatar creation, I noticed that, to achieve proper root motion for a non-humanoid model, avatar creation alone is not enough. Even when the non-humanoid avatar is created and the animator's applyRootMotion is set to true, the model's gameobject isn't moved by the animator component during play mode. I think the imported animation assets needs to be setup correctly for them to be able to apply their motion to the model gameobject.

EDIT 2

This issue goes hand-in-hand with another issue I reported regarding Humanoid models: #874

Steps to reproduce 🔢

Import the FBX and GLB from this zip and see that FBX model has an avatar and UnityGLTF model doesn't have an avatar.
https://github.com/user-attachments/files/20718763/Horse.zip

Files to reproduce the issue ♻

https://github.com/user-attachments/files/20718763/Horse.zip

Editor Version 🎲

Other (Provide details below)

Render Pipeline and version

Not relevant

UnityGLTF Version

2.17.1

Operating System 👩‍💻

Windows

When does this problem happen?

• Editor Import
• Runtime Import
• Editor Export
• Runtime Export

Additional Info 📜

No response

Validations 🩹

• I have searched existing issues: no issue already exist that reports the same problem.
• I follow the Code of Conduct
• I provided a minimal reproducible example, including files when necessary.

[XtroTheArctic]

As I mentioned in the other issue which goes hand-in-hand with this one (#874 (comment)), importing GLTF animations with root motion support seems impossible due to Unity's black box implementation of its FBX importer and AnimationClip creation.

This unfortunate outcome is somewhat OK for humanoid GLTF models because, through the humanoid avatar, we can still apply FBX based root motion animations to humanoid GLTF models.

For this current non-humanoid root motion issue thou, it won't be as easy as it is for humanoid GLTF models because I couldn't find a way to apply FBX based animations onto non-humanoid GLTF models yet.

I'll continue investigating this... :(

[XtroTheArctic]

OMG OMG OMG!!! It was so very much hard to investigate/debug/test/figure out this problem. It took many days with heavy brain effort with lots of pain but I finally did it!

First of all, working on an existing horse model and its animation was extremely hard so I decided to make a very simple cylinder model and animate it very basically. In the video below, you can see snake like animation and the applied root motion at the same time. Please ignore the horses. They were my earlier attempts which are still broken.

Secondly but more importantly, and unfortunately, UnityGLTF alone is not enough to make this work (animating and applying root motion) so I had to invent a mixed method: Import the non-humanoid model as GLTF and import its animation as FBX !!! Yes, you heard that right. The reason for this is... (as I mentioned in humanoid version of this issue: #874 (comment)) Unity's AnimationClip creation is a very tight black box and importing an animation with root motion support is almost impossible for UnityGLTF (or anyone else).

To be able to apply FBX animation to GLTF model properly, it took so many trials and errors to find the correct Blender export setup and Unity import setup (both on GLTF model, and FBX animation). I won't go into those details here but I may be able to share them in my upcoming PR for resolving this issue.

Screen.Recording.2025-06-25.210801.mp4

[XtroTheArctic]

Finally, I made root motion work on my horse model (it's a 3rd party model but anyways). I'll submit the PR soon.

Screen.Recording.2025-06-26.193542.mp4

[XtroTheArctic]

PR submitted: #877