Undefined access when anim component with multiple layers is cloned

[LeXXik]

Application crashes, when trying to clone an entity with an Anim Component that has more than 1 animation layer.

Repro:
Open engine example: https://playcanvas.github.io/#/animation/layer-masks
And add to the end:

modelEntity.clone();

[kungfooman]

vote for clone button in every example - such a good Litmus test 😅 🙈

The lack of JSDoc makes it hard to figure out, but I got this to work anyway:

const clone = pc.app.root.children[2].clone();
pc.app.root.addChild(clone);
clone.translate(0.5, 0, 0);

I saw multiple issues:

1. Using object spreading for... cloning?

Example:

class Test {
    _hi = 123;
    get hi() {
        return _hi;
    }
}
test = new Test();
const obj = {...test};
console.log("obj", obj);

Outputs: {_hi: 123}, but we need {hi: 123}!

Happens in two places:

engine/src/framework/components/anim/component.js

Lines 378 to 383 in e3217c4

	for (let i = 0; i < stateGraph.layers.length; i++) {
	const layer = stateGraph.layers[i];
	this._addLayer({ ...layer });
	if (layer.states.some(state => state.blendTree)) {
	containsBlendTree = true;
	}

engine/src/framework/anim/controller/anim-controller.js

Lines 131 to 134 in e3217c4

	this._transitions = transitions.map((transition) => {
	return new AnimTransition({
	...transition
	});

2. data.stateGraph lacks extra layer

engine/src/framework/components/anim/system.js

Lines 46 to 49 in e3217c4

	if (data.stateGraph) {
	component.stateGraph = data.stateGraph;
	component.loadStateGraph(component.stateGraph);
	}

You can hack it up like this for making it work:

        if (data.stateGraph) {
            data.stateGraph.layers[0] = data.layers[0]; // hack
            data.stateGraph.layers[1] = data.layers[1]; // hack
            component.stateGraph = data.stateGraph;
            component.loadStateGraph(component.stateGraph);
        }

And then there are even more issues, just simple type bugs basically. The component just needs more JSDoc and such issues would be automatically detectable.

I tried it in the past, but it was blocked: #2986

[willeastcott]

vote for clone button in every example - such a good Litmus test 😅 🙈

I would suggest that the unit tests are designed exactly for checking this type of thing rather than the examples.