RealityKit – Rotating an Entity affects its Scale - swift

Question

I am loading an entity using the USDZ file. I want after loading the entity, I want to rotate is forever. I am using the following code.
cancellable = ModelEntity.loadAsync(named: "toy_drummer").sink { [weak self] completion in
if case let .failure(error) = completion {
print("Unable to load model \(error)")
}
self?.cancellable?.cancel()
} receiveValue: { entity in
anchor.addChild(entity)
arView.scene.addAnchor(anchor)
let rotation = Transform(pitch: 0, yaw: .pi, roll: 0)
entity.move(to: rotation,
relativeTo: nil,
duration: 15.0,
timingFunction: .linear)
}
Instead of rotating correctly, the entity is scaling and getting bigger and bigger. Any ideas?

Answer 1

You need a starting transform "point" and ending transform "point". If a value of referenceEntity (relativeTo) argument equal to nil it means relative to world space. Since the same 4x4 matrix slots are used for rotation values ​​as for scaling, when the model is rotated, its scale also changes at the same time, if there is a difference in scale.
For perpetual transform animation use some of RealityKit 2.0 tricks.
And, of course, there is a Trigonometry that was really conceived for perpetual orbiting.
Here's a correct version of your code:
import UIKit
import RealityKit
import Combine
class ViewController: UIViewController {
#IBOutlet var arView: ARView!
var cancellable: Cancellable? = nil
let anchor = AnchorEntity()
override func viewDidLoad() {
super.viewDidLoad()
cancellable = ModelEntity.loadAsync(named: "drummer.usdz").sink { _ in
self.cancellable?.cancel()
} receiveValue: { entity in
self.anchor.addChild(entity)
self.arView.scene.addAnchor(self.anchor)
let rotation = Transform(pitch: 0, yaw: .pi, roll: 0)
entity.move(to: rotation,
relativeTo: entity,
duration: 5.0,
timingFunction: .linear)
}
}
}

Answer 2

I made a swift package a couple of years ago, RealityUI, which does include animations like a continuous rotation:
https://github.com/maxxfrazer/RealityUI/wiki/Animations#spin
You'd just need to include the package, and call:
entity.ruiSpin(by: [0, 1, 0], period: 1)
docs here:
https://maxxfrazer.github.io/RealityUI/Extensions/Entity.html#/s:10RealityKit6EntityC0A2UIE7ruiSpin2by6period5times10completionys5SIMD3VySfG_SdSiyycSgtF