Objects with shared NLA tracks from Blender are strangely linked

[j-conrad]

When two objects in a glTF have NLA tracks on them that are shared between them, the viewer exhibits strange behavior when attempting to toggle the various animations.

In the provided example file, Torus and Cube share an animation track in common called TorusAction.
If I check or uncheck either TorusAction, it automatically toggles the other TorusAction. But this does not always match up with what animations are actually playing in the 3d view. Sometimes both animations play, neither play, or only one or the other plays.

I'm not sure if there's a way for the viewer's UI to indicate which actions are on which objects, but that could be a start to understanding what's going on.

I've included both the .blend and the .glb

AnimationExportTEST.zip

[donmccurdy]

Looks like I've made some incorrect assumptions about clip.name being unique:

three-gltf-viewer/src/viewer.js

Lines 679 to 688 in 9ef59ab

	this.clips.forEach((clip, clipIndex) => {
	// Autoplay the first clip.
	let action;
	if (clipIndex === 0) {
	actionStates[clip.name] = true;
	action = this.mixer.clipAction(clip);
	action.play();
	} else {
	actionStates[clip.name] = false;
	}

... that said, using unique names is really a good idea across the board. Object3Ds/Meshes are also expected to have unique names for animation in three.js. I'm wondering if the exporter should be doing something to deduplicate these. 😕

[looeee]

Continuing the discussion from discourse. Here's the original FBX discussed there.

ShineGreymon.zip

Converted to glb with FBX2GLTF. There are multiple animation tracks with the same name.

chr776.glb.zip

I'm wondering if the exporter should be doing something to deduplicate these. 😕

In this case, we don't know the original exporter (something called Unity Studio, possibly). However, maybe FBX2GLTF should be de-duplicating names. That said, there's nothing I could find in the glTF spec that says duplicate names are forbidden, so maybe it's the responsibility of the loader/viewer to handle this?

I've opened an issue on FBX2GLTF so let's see what they have to say: facebookincubator/FBX2glTF#273

EDIT: possibly related - mrdoob/three.js#15087

[donmccurdy]

Fixed in most recent release. ✅