onMount method
Called when the owning node enters a live scene graph.
Implementation
@override
void onMount() {
final renderScene = node.internalRenderScene;
if (renderScene == null) return;
final item =
RenderItem(
geometry: instancedMesh.geometry,
material: instancedMesh.material,
)
..sourceNode = node
..drawSource = instancedMesh;
_renderItem = item;
renderScene.add(item);
}