Core: Convert Object3D and EventDispatcher to ES6 classes.

[Mugen87]

Related issue: -

Description

Converts the remaining two class in the src/core folder.

[Mugen87]

WebXRManager also has been updated. Otherwise EventDispatcher can't be an ES6 class.

[mrdoob]

Thanks!

[drcmda]

@Mugen87 do you still remember what prompted this change https://github.com/mrdoob/three.js/blob/master/src/core/Object3D.js#L66-L94

const v = new THREE.Vector3()
const m = new THREE.Mesh()
m.position = v

the request we got was that people want to wire up their own objects which they can then control outside of the class. but it seems these props can't get overwritten any longer. looks like some props are non-replaceable while some others are (matrix, layers). could this block be removed so that all props can be driven externally?

[mrdoob]

It was a bad practice.

People did this a lot:

mesh.position = new THREE.Vector3(1,1,1)

Instead of

mesh.position.set(1,1,1)

And they would do that in loops and would create a lot of garbage.

That pattern also broke mesh.rotation which we need to track to create mesh.quaternion.

[drcmda]

for reference pmndrs/react-three-fiber#1419 they want to drive matrix externally, which is similar, mesh.matrix = externalMatrix. if this is the intended direction, i would communicate that overwriting props in threejs is no longer accepted.

[mrdoob]

It definitely is discouraged.

[drcmda]

understood. im glad i opted for .copy for <mesh position={external} some years ago ☺️