[Merged by Bors] - expose extras from gltf nodes

[mockersf]

fixes #2153

expose the extras field value as a string

[cart]

Lazy questions:

• How often are "extras" defined in gltf files
• Is gltf_node.extras() None when gltf extras aren't defined in the file? I'm assuming the answer is yes. I just want to sanity check that we aren't allocating a bunch of empty strings per-node/entity each time we spawn a GLTF scene.

[NathanSWard]

I just want to sanity check that we aren't allocating a bunch of empty strings per-node/entity each time we spawn a GLTF scene.

Depending on this, we could always put this behind a feature flag (disabled by default) to avoid the extra allocations. 🤷

[mockersf]

• How often are "extras" defined in gltf files

I don't know, I didn't saw yet in a model I used but it seems a nice place to put some metadata that I put in code until now

• Is gltf_node.extras() None when gltf extras aren't defined in the file? I'm assuming the answer is yes. I just want to sanity check that we aren't allocating a bunch of empty strings per-node/entity each time we spawn a GLTF scene.

Yup, just checked with FlightHelmet, no extras added

[cart]

Just checked out a complicated gltf from my game High Hat and extras weren't defined.

[cart]

It looks like blender doesn't include extras by default. I think validating that other popular 3d packages dont include extras unless the user defines them is probably the "complete" solution here, but I understand that this hard to verify. Can we just "randomly" sample a few free gltf assets from some "model sharing" website and see if they include the field?

[mockersf]

I didn't find files with those in my random sample of files on my drive that I collected here and there (kenney's assets and a few other free downloads), and it seems only babylon.js supports this out of the box (but that's easy as json support is native in js...)

On the other hand I don't think it add much code or complexity, but it does add an extra component with a string that the user will have to deserialize... not the nicest UX

Also it's part of the spec: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#extras

I think Maya can support extras if user defines custom attributes https://doc.babylonjs.com/extensions/Exporters/Maya_to_glTF#custom-attributes

[quinnyo]

I would like to see this feature in bevy. I often find situations/projects where I want to be able to specify some metadata in a 3D package (Blender) and have it exported with the scene/model. GLTF extras is a solution to this problem.

Some points:

• extras can be included with many(/most/all?) gltf object types -- not just nodes
• I think it would be acceptable to only support / expect the extras data type to be a json object
• the gltf spec recommends using the object data type as a best practice
• Blender specific:
  • Blender exports 'Custom Properties' as extras if an option is enabled when exporting
  • the property values can be complex (~json objects) -- e.g. a value of [1, 2, 3] in Blender will be exported as an array of integers
  • Custom Properties in the Scene, Object, Object Data (Mesh), and Material are exported to their GLTF counterparts
  • https://docs.blender.org/manual/en/latest/addons/import_export/scene_gltf2.html#custom-properties

[nicopap]

I can confirm this could be very helpful. Currently working around the limitation with a trait that just pushes components on nodes with specific names. my skin hook impl

[cart]

We've been steadily increasing the number of "per entity string allocations" when instancing GLTF scenes. I think we should prioritize "proper string cows" in the very near future to keep this behavior in check.

[cart]

bors r+

[bors]

Pull request successfully merged into main.

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