bevy 0.12 system for spawning a `GltfNode` from `Handle<GltfNode>`

spawn_gltf_node.rs

fn gltf_node_spawner(
    mut commands: Commands,
    node_handles: Query<(Entity, &Handle<GltfNode>), Added<Handle<GltfNode>>>,
    assets_gltf_nodes: Res<Assets<GltfNode>>,
    assets_gltf_mesh: Res<Assets<GltfMesh>>,
) {
    for (parent, handle) in &node_handles {
        let Some(node) = assets_gltf_nodes.get(handle) else {
            warn!("GltfNode not found: entity {:?}, {:?}", parent, handle);
            continue;
        };

        // because the root GltfNode has a Transform component, we need to
        // start loading the node in a child entity.  If we don't do this,
        // modifying the `Transform` on the `Handle<GltfNode>` entity will
        // warp the mesh.
        let node_entity = commands
            .spawn(SpatialBundle::default())
            .set_parent(parent)
            .id();
        let mut node_queue: VecDeque<(Entity, &GltfNode)> = VecDeque::from([(node_entity, node)]);

        while let Some((node_entity, node)) = node_queue.pop_front() {
            // create a child entity for each of the GltfNode children and
            // queue it for processing
            let mut children: Vec<Entity> = node
                .children
                .iter()
                .map(|child_node| {
                    let child = commands.spawn_empty().id();
                    node_queue.push_back((child, &child_node));
                    child
                })
                .collect();

            // If the GltfNode has a GltfMesh, process it now and add any
            // children to the list.
            if let Some(handle) = &node.mesh {
                if let Some(gltf_mesh) = assets_gltf_mesh.get(handle) {
                    // create a PbrBundle child for every primitive in the
                    // GltfMesh
                    for primitive in gltf_mesh.primitives.iter() {
                        let child = commands.spawn(PbrBundle {
                            mesh: primitive.mesh.clone_weak(),
                            material: primitive
                                .material
                                .as_ref()
                                .expect("primitive to have a material")
                                .clone_weak(),
                            ..default()
                        });
                        children.push(child.id());
                    }
                } else {
                    warn!("GltfMesh not found: entity {:?}, {:?}", node_entity, handle);
                }
            }

            commands
                .entity(node_entity)
                .push_children(&children)
                .insert(SpatialBundle {
                    transform: node.transform,
                    ..default()
                });
        }
    }
}