KHR_node_visibility support

[aaronfranke]

Is your feature request related to a problem? Please describe.
In Godot 4.4 and earlier, invisible nodes were excluded from export. In Godot 4.5 and later, we added support for KHR_node_visibility, and made it a required extension on export, which ensures that user models are always rendered correctly (or not at all), and users have to opt-in to allow their models to be rendered incorrectly. If this was optional by default, the display of models exported by the user may end up changing without their knowledge. However, this required by default choice means such models can't be imported into Blender, which does not yet support this extension.

Describe the solution you'd like
Implement this Khronos extension, KHR_node_visibility: KhronosGroup/glTF#2410

Describe alternatives you've considered
The only alternative is to wait, it needs to be done this way, with this extension. It is possible that any extension may be changed prior to ratification, but... this is a simple boolean, it's not going to change.

Additional context
This extension is already implemented in:
Godot: godotengine/godot#93722
Unity: KhronosGroup/UnityGLTF#822
Babylon.JS: BabylonJS/Babylon.js#15754 and https://doc.babylonjs.com/typedoc/classes/BABYLON.GLTF2.Loader.Extensions.KHR_node_visibility
StereoKit: StereoKit/StereoKit#1231 (not yet merged)
glTF Sample Viewer: https://github.khronos.org/glTF-Sample-Viewer-Release/interactivity/

Issues tracking this in other projects:
Bevy: bevyengine/bevy#17524

[julienduroure]

Hello,
Policy of the glTF I/O in Blender is to support only officially ratified extensions.
Setting as enhancement, waiting extension status progress.

[The0Dev]

I wonder how this extension could be fully implemented in Blender, given that the boolean property is designed to control the visibility of the node it belongs to, along with all its child nodes recursively. However, in Blender, visibility is not inheritable and does not impact child nodes. While this may not pose an issue during import, it could be problematic during export, especially when used in conjunction with animations. This would likely require some changes to Blender.

[scurest]

Note that the node hierarchy is altered on both import and export, so it would be non-trivial even if Blender did have "hide whole subtree".

[julienduroure]

Some thoughts - to be sure to not forget them when time comes to think about about to implement it:

The glTF behavior seems to be equivalent to the blender Collection visibility : recursive & priority on higher nodes.
Except that the Collection visibility can not be animated,where glTF visibility can, by KHR_animation_pointer