Implement KHR_node_visibility in the GLTF module

[aaronfranke]

Implements KHR_node_visibility KhronosGroup/glTF#2410 in Godot, which allows glTF nodes to be marked as not visible. Both import and export are supported.

Details: The glTF visibility system works the same as Godot's visibility system, only affecting visuals, which makes this really easy to implement. Since this extension was extremely simple, I decided to just implement it in GLTFDocument rather than writing a GLTFDocumentExtension class for it. I also made it a required extension on export, to ensure that user assets are always rendered correctly (EDIT: Required by default, but users can customize this on export). However most scenes don't contain invisible objects, so this won't impact most scenes.

Test file: cube_visibility_example.zip

[fire]

I mentioned this proposal at the gltf meeting so I agree with it. Did not test yet.

[fire]

We had a lengthy discussion of the support of the visibility extension if we make it required.

Required extension for something cosmetic is a bad idea IMHO

Required extensions will make godot look bad and create a support headache

[aaronfranke]

Updated the PR to make this configurable on export:

[akien-mga]

Shouldn't we wait for Khronos to approve the draft proposal before merging its implementation? If they reject it, but we merge it, we'd be stuck maintaining a non-standard extension.

[aaronfranke]

@akien-mga Indeed, we can wait for approval. I doubt this will change but I cannot absolutely guarantee that.

[fire]

We discussed on Thursday that the moment Khronos ratifies the extension we are clear to merge.

[aaronfranke]

Marking as draft to prevent accidental merging before ratification. However, the code is complete and ready for review (well, it has already been reviewed, but more review is welcome too).

[yankscally]

Honestly, it is only a single bool, its not that deep. and, it has a lot of value to godot when blender and godot share this eye icon in the same panel. I think it's worth supporting and then hotfixing later if Khronos happen to change their mind.

[aaronfranke]

KHR_node_visibility support has been added to the BabylonJS game engine: BabylonJS/Babylon.js#15754

[fire]

My thinking at this time is we should add this to 4.5 and if KHR_mode_visibility is not released we ship it in Godot Engine 4.5.

Any arguments?

[lyuma]

I think the fact that BabylonJS added visibility should be a good argument that Godot could add it as well. Is there a reason to wait for ratification?

[aaronfranke]

@lyuma I would be happy to go through with this. Can you give it a review/approval?

[lyuma]

Looks good.

If there is a place to write documentation, it might be good to document a bit more clearly what "Include & Required" means.
Perhaps instead of visibility mode, some terminology like "hidden nodes" might be easier for users to understand since the visibility mode only affects nodes which are hidden.

[Repiteo]

Thanks!