Generate thumbnails on imported scenes.

[SaracenOne]

Ends a somewhat long-standing discontinuity of the imported scenes (FBX, GLTF, Collada, ect.) not having any thumbnail previews like regular Godot scenes. It does this by providing a hook step where they can be generated and cached upon reimport.

Keeping this in draft for now since it could probably benefit from further refactoring, improving bounds calculations for skinned meshes, and adding displayable gizmos for the cases where no mesh instances could be found (animation or collision-only imports, for example).

• Production edit: This closes Display scene resource thumbnails in the FileSystem dock godot-proposals#8760.

[JekSun97]

In editor_inteface.cpp error in the comment on line 300

[fire]

@SaracenOne Do you think this can be done for the 4.4 cycle?

[Calinou]

Tested locally (rebased on top of master f952bfe), it works as expected.

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Note that you must reimport the scene for the preview to be generated (existing projects won't have one automatically created). Also, it can take a few seconds for the icon to appear in the FileSystem dock after reimporting.

For some assets, it results in a gray preview, presumably due to skinning resulting in a different AABB than needed. This happens with player.glb from the 3D Platformer demo:

Also, cube.glb from the Global Illumination demo is too zoomed in:

zdm2.glb from the same demo is fine though:

[fire]

Going to do a rebase and push it.

[fire]

We discussed how the thumbnail in imported scenes needs features added.

1. AABB estimation related to skinned meshes has also proven a pain point for the advanced importer.
2. Provide an API allowing more thumbnail generation customization for regular Godot scenes.

What do you think about greenlighting the pull request as is and revisiting thumbnails in imported scenes feature enhancements later to see if it can be improved?

[fire]

Please take a look at the previous comment for the summary.

@Calinou mentioned that we should not wait for the entire feature list to be implemented since it's already an improvement over what we have now.

[Repiteo]

Accepting with the expectation that this will be followed up on soon™ with the aforementioned features

[Repiteo]

Thanks!