DirectGeometry: clone bounding volumes in fromGeometry method

[WJsjtu]

See #13420 for detail.
@Mugen87 The doc may need to be fixed, but I'm not sure whether to remove all the information about EventDispatcher in it or to make DirectGeometry extend EventDispatcher and add dispose method ( like BufferGeometry and Geometry ).

As I mentioned in PR 13420, The same code may need to be added in BufferGeometry.updateFromObject for Mesh and Points.

[WestLangley]

I do not think it makes sense to add these methods here.

DirectGeometry is a temporary data structure, and IMO does not require a separate class. I would remove it completely, and inline the fromGeometry() code in the single place it is used.

[WJsjtu]

@WestLangley You are right, of course the code of DirectGeometry can be moved to Geometry and BufferGeometry (IMO maybe the InterleavedBuffer.js and InterleavedBufferAttribute.js have the same problem). And this is a design matter. what I cared at first is about the cloning behavior which is related to the problem of whether DirectGeometry should have bounding volumes mentioned in PR13420.

[WestLangley]

I understand. I guess @mrdoob will make the design decision. Thank you for pointing out these issues. :)

[Mugen87]

@WJsjtu I would focus on bounding volumes in this PR. If you like, you can remove DirectGeometry.computeBoundingSphere() and DirectGeometry.computeBoundingBox() from the docs. Otherwise perform the changes on the docs at once in a separate PR.

[mrdoob]

Hmm... I'm not sure DirectGeometry's boundingBox and/or boundingSphere is being used anywhere...?

[Mugen87]

They are copied in BufferGeometry.fromDirectGeometry().

three.js/src/core/BufferGeometry.js

Lines 573 to 583 in 0c6c005

	if ( geometry.boundingSphere !== null ) {
	this.boundingSphere = geometry.boundingSphere.clone();
	}
	if ( geometry.boundingBox !== null ) {
	this.boundingBox = geometry.boundingBox.clone();
	}

[mrdoob]

Oh, there you go. I should have named that variable directgeometry.
Okay, will take a look next cycle...

[Mugen87]

@mrdoob I think it's okay to merge this fix for consistency reasons.

[mrdoob]

Thanks!