Animate rotation of an Entity

I am fairly new to the ARKit / RealityKit and I want to animate the rotation of a loaded USDZ model. Unfortunately, I can't get it to work.

guard let modelEntity = try? Entity.loadModel(named: "toy_biplane_idle") else {
      return
}
anchorEntity.addChild(modelEntity)
var rotationTransform: Transform = Transform()
rotationTransform.rotation = .init(angle: 30 * .pi / 180, axis: .init(x: 1, y: 1, z: 1))
// modelEntity.orientation = rotationTransform.rotation // this works but is not animated
modelEntity.move(to: rotationTransform, relativeTo: modelEntity.parent, duration: 1.0) // no effect at all

I tried to use the move(to: method with a duration but it has no effect at all, there is neither animation nor any rotation. What am I doing wrong ?

Solution

First Approach | .move(..) method

In iOS, you have to apply the move(..) method after appending the biplane model to the scene:

import SwiftUI
import RealityKit

struct ContentView : View {
    var body: some View {
        ARBiplaneView()
            .ignoresSafeArea()
    }
}
struct ARBiplaneView : UIViewRepresentable {
    let arView = ARView(frame: .zero)
    let anchor = AnchorEntity()
    
    func makeUIView(context: Context) -> ARView {
        let modelEntity = try! Entity.loadModel(named: "toy_biplane_idle")
        modelEntity.scale *= 4
        anchor.addChild(modelEntity)
    
        var transform: Transform = Transform()
        transform.translation.z = -2.0
        transform.rotation = .init(angle: .pi/2, axis: [0,1,0])
        
        // doesn't work here
        // modelEntity.move(to: transform, relativeTo: modelEntity, duration: 5.0)

        arView.scene.anchors.append(anchor)
        
        // DOES WORK HERE
        modelEntity.move(to: transform, relativeTo: modelEntity, duration: 5.0)
        
        return arView
    }
    func updateUIView(_ view: ARView, context: Context) { }
}

Second Approach | FromToByAnimation value

The only disappointment when using this approach is that repeatMode pty doesn't work in Xcode 16. I hope this feature will be fixed soon.

func makeUIView(context: Context) -> ARView {
    model.scale *= 4
    model.transform.rotation = simd_quatf(angle: .pi, axis: [0, 1, 0])
    let transform = model.transform
    
    model.transform.rotation *= simd_quatf(angle: -.pi, axis: [0, 1, 0])
    let definition = FromToByAnimation(to: transform, duration: 2, bindTarget: .transform, repeatMode: .none)
    let animationView = AnimationView(source: definition)
    if let resource = try? AnimationResource.generate(with: animationView) {
        // model.playAnimation(resource.repeat())
        model.playAnimation(resource)
    }
    anchor.addChild(model)
    arView.scene.anchors.append(anchor)
    return arView
}