Set the unlit / unshaded extension when importing / exporting GLTF

[hakro]

Fixes #74268

[clayjohn]

Looks good to me!

[lyuma]

KHR_materials_unlit must also be added into the document's top-level extensionsUsed dictionary?

I'm asking some gltf nerds just to double-check if this is true, but I'm pretty sure.

[hakro]

KHR_materials_unlit must also be added into the document's top-level extensionsUsed dictionary?

I'm asking some gltf nerds just to double-check if this is true, but I'm pretty sure.

Good catch, thank you.
I missed it, since the import in blender worked fine.
But you're right, it's better to have it as it's documented here:
https://github.com/KhronosGroup/glTF/blob/main/extensions/README.md#about-gltf-extensions

I checked how Blender also does the export, and the dictionnary is there as well.

Now the export from Godot looks like this :

Cheers !

[akien-mga]

Thanks!

[YuriSizov]

Cherry-picked for 4.0.1.