Better implementation of humanoid avatar creation (use hierarchy instead of names)

[ostef]

Describe the bug 💬

(not a bug but choosing a different issue template does not work)

Humanoid avatar creation has been a pain point for a few people it seems (me included), especially considering there is no way to configure it.

As others have mentioned the way the FBX importer handles this is opaque and undisclosed, but one thing I am certain of is that it does not care about the names of the bones (apart maybe to differentiate left and right bones). It only expects a specific hierarchy.

We should find the hips bone, which is the first bone with three children including two that have respectively a .L and .R suffix.
Then we walk the .L and .R bones which are the legs, first bone is upper leg, seconds lower, third is the foot etc.
The last child of the hips is the spine, walk along it until we find the same pattern as the hips, .L is left arm and .R the right.
If the arms only contain three bones then we skip the shoulder, because it's optional.

You get the idea.

Here's a rig I made without renaming the bones apart from .L and .R suffixes, everything gets assigned automatically correctly:

I have attached both a .glb and .fbx file of the rig.

Steps to reproduce 🔢

Rigs.zip

Files to reproduce the issue ♻

No response

Editor Version 🎲

6000.0

Render Pipeline and version

URP

UnityGLTF Version

2.20.0

Operating System 👩‍💻

Linux

When does this problem happen?

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

Additional Info 📜

@XtroTheArctic this is probably of interest to you.

I might make a PR myself and implement this since it's not that big of a change. Maybe we should keep the name dictionary just so other people's rigs that worked don't get broken (although if they do get broken they probably didn't respect the hierarchy that mecanim expects anyway).

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 far as I can see, UnityGLTF importer was implemented to match the bone names only (additionally checking some predefined naming variations).

Implementing a bone hierarchy detection will be difficult but I may be interested in working on this with some pre-conditions. This work probably will conflict with my earlier related PRs so they need to be reviewed and merged first:
#860
#877

@robertdorn83 I resolved the conflicts on those PRs above as you requested, if you have a chance to review them.

@ostef Have you seen my "feedback feature for avatar bones"? It doesn't give you a configuration option like FBX importer does but it lets you make sure if all bones are detected correctly. As I mentioned above, the PR isn't merged yet. IF you are interested in using it, you can switch to my fork of UnityGLTF temporarily: https://github.com/XtroTheArctic/UnityGLTF

[ostef]

Yes I've seen your PR, nice work! I didn't switch because I would prefer staying on the main repo or at least one I have control over. Besides, I had identified that naming bones differently would work for me.

I don't think it's difficult, I will implement something. I don't think it will conflict with your other PRs as it's probably only modifying the AvatarUtils file.

[ostef]

Actually I have more problems with the way my animations turn out with this GLTF importer which I unfortunately don't have time to debug. I used GLTF because it seemed the most smooth with the way I use Blender and have set up my rigs, but I can probably export as FBX which has a much better support.

I won't spend time making the full hierarchy walk algorithm and testing it then, but I was thinking about something like this, if you want to delve into it (untested).

private static Transform FindHips(Transform root, out Transform leftLeg, out Transform rightLeg, out Transform spine) {
    if (root.childCount == 3) {
        Transform leftChild = null;
        Transform rightChild = null;
        Transform spineChild = null;
        
        for (int i = 0; i < root.childCount; i += 1) {
            var child = root.GetChild(i);
            if (child.gameObject.name.EndsWith(".L")) {
                leftChild = child;
            } else if (child.gameObject.name.EndsWith(".R")) {
                rightChild = child;
            } else {
                spineChild = child;
            }
        }
    
        if (leftChild != null && rightChild != null && spineChild != null) {
            leftLeg = leftChild;
            rightLeg = rightChild;
            spine = spineChild;
            return root;
        }   
    }

    for (int i = 0; i < root.childCount; i += 1) {
        var child = root.GetChild(i);
        var hips = FindHips(child, out leftLeg, out rightLeg, out spine);
        if (hips != null) {
            return hips;
        }
    }
    
    return null;
}

private static bool FindBones(Transform root) {
    Transform leftLeg = null;
    Transform rightLeg = null;
    Transform spine = null;
    
    var hips = FindHips(root, out leftLeg, out rightLeg, out spine);
    if (hips == null) {
        return false;
    }
    
    // Use a similar logic to find neck/head and right & left arms from the spine
    // Make sure to limit the number of recursive calls because the spine can only be three bone long at maximum (and spine1 and spine2 are optional)
    // You can also walk the spine iteratively
    
    return true;
}

[XtroTheArctic]

GLTF is very superior to good old FBX. I strongly suggest you keep using it. Animation problems can be solved. In one of my bug tickets or PRs, I mentioned how I export the model as glb and its animations separately as FBX. If you are interested, I can give you more info.

This separate FBX animation thing is for retargeting humanoid animations onto other avatars. If your model has its own custom animations (a custom animal for example), you don't even have to separate the animations. They can come in the same glb automatically.

[robertdorn83]

Hey, sounds good to me so far. This could also just be a Importer Inspector Method to assign the bones this way.
So like here, with the new view from XtroTheArctic, there could be a Menu/Tool Button or so to provide such functionality

[XtroTheArctic]

Nice idea.

I'll keep this in mind if I manage to find some time to work on this request hopefully soon.