Scene exporting toJSON results in inconsistent values for Directional & Spot Lights

[trapgar]

Description

If you have a scene that includes a directional light without a target, the ObjectLoader defaults to the target to a new Object3D(). This means that on export, the target will be serialized as a brand new uuid.

Then when the scene is deserialized with parseAsync etc., bindLightTargets will not be able to find the target (as the target pointed to a new Object3D, and so will default to another new Object3D.

This means that every export-to-json & import-from-json for the exact same scene w/o edits will continue to alter the resulting text.

Reproduction steps

1. Go to https://threejs.org/editor/
2. File > New > Pong
3. Project > Publish
4. File > New > Pong
5. Project > Publish

Compare the app.json of the 2 exports - the last child in the pong app is a DirectionalLight; the "target": <uuid>" values will differ.

Code

src/loaders/ObjectLoader.js:1212

bindLightTargets(object) {
	object.traverse(function (child) {
		if (child.isDirectionalLight || child.isSpotLight) {
			const uuid = child.target;
			const target = object.getObjectByProperty('uuid', uuid);

			if (target !== undefined) {
				child.target = target;
			}
			else {
				child.target = new Object3D();
			}
		}
	});
}

if (target !== undefined) && child.target = new Object3D(); are the important parts

Live example

• jsfiddle-latest-release WebGLRenderer
• jsfiddle-dev WebGLRenderer
• jsfiddle-latest-release WebGPURenderer
• jsfiddle-dev WebGPURenderer

Screenshots

Version

0.174.0

Device

No response

Browser

No response

OS

No response

[trapgar]

I would suggest either supporting no target for those objects, or creating an Object3D.Empty with a uuid of 00000000-0000-0000-0000-000000000000 and make that the default instead. I don't have time right now to create a PR, but will when I can if someone else doesn't resolve this 1st.

[Mugen87]

This means that every export-to-json & import-from-json for the exact same scene w/o edits will continue to alter the resulting text.

The target is properly serialized and deserialized if it is part of the scene. You are seeing this issue in the Pong demo because a) it's JSON is old does not have the target UUID defined in the first place and b) the target is not editable in the editor.

[Mugen87]

I hesitated a bit but I think this issue is a duplicate of #9508.

If the target would be added to the scene graph in the editor, serialization/deserialization would work as expected. It would also be a good idea to update the JSON preset for the examples so a target is defined in the JSON as well (otherwise you would see new UUIDs on each File > New > Pong again).

[trapgar]

Issue does not appear to be the result of pong being an older version. You can also reproduce this by:

1. File > New > Pong
2. Project > Publish
3. File > Open the app.json you just exported
4. Project > Publish

or

1. File > New > Empty
2. Add > Light > Spot
3. Project > Publish
4. File > Open the app.json you just exported
5. Project > Publish

The target uuid will have changed again.

[Mugen87]

Yes, it's because the target is never added to the scene. #9508 tracks that.