RealityKit - Animate opacity of a ModelEntity?

Question

By setting the color of a material on the model property of a ModelEntity, I can alter the opacity/alpha of an object. But how do you animate this?

Answer 1

I tested it using different techniques and came to the sad conclusion: you can't animate a material's opacity in RealityKit framework because RealityKit materials don't support animation at runtime (for now I hope). Let's wait for RealityKit's major update.

Here's a code you can use for test

(arView.alpha property just works):

import UIKit
import RealityKit

class ViewController: UIViewController {

    @IBOutlet var arView: ARView!

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        arView.alpha = 1.0 
        opacityAnimation()
    }

    func opacityAnimation() {

        UIView.animate(withDuration: 5.0,
                         animations: {

            self.arView.alpha = 0.0
        })
    }
}

And use this code snippet in order to make sure that animation doesn't work properly

(there's no animation process, just value assignment):

import UIKit
import RealityKit

class ViewController: UIViewController {

    @IBOutlet var arView: ARView!
    let tetheringAnchor = AnchorEntity(world: [0,0,0])
    var material = SimpleMaterial()
    let mesh: MeshResource = .generateSphere(radius: 0.5)
    var sphereComponent: ModelComponent? = nil

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        material.metallic = .float(1.0)
        material.roughness = .float(0.0)
        material.baseColor = .color(.red)

        sphereComponent = ModelComponent(mesh: mesh,
                                    materials: [material])

        tetheringAnchor.components.set(sphereComponent!)
        arView.scene.anchors.append(tetheringAnchor)

        opacityAnimation()
    }

    func opacityAnimation() {

        UIView.animate(withDuration: 5.0,
                         animations: {

            self.material.metallic = .float(1.0)
            self.material.roughness = .float(0.0)
            self.material.baseColor = .color(.green)

            self.sphereComponent = ModelComponent(mesh: self.mesh,
                                             materials: [self.material])

            self.tetheringAnchor.components.set(self.sphereComponent!)
            self.arView.scene.anchors.append(self.tetheringAnchor)
        })
    }
}