RealityKit - Hiding and showing parts (meshes) of usdz model

Question

I need an advice. I am using RealityKit for showing models of fences. I have models which has several meshes that shouldn't be shown at once. For example filling of the fence. There are different options and I have it all in my model:

I would like to show always one at the time. How can I do that? I can't edit meshes at runtime, can I? I was thinking about changing material for each mesh but when I tried to set clear color with SimpleMaterial it shows mesh in black and when I tried OcclusionMateril I get this result:

Example how I tried hide material with SimpleMaterial:

var material = SimpleMaterial()
material.baseColor = MaterialColorParameter.color(UIColor.clear)
material.tintColor = .clear
clonedEntity.model?.materials[index] = material

Or with OcclusionMaterial (in screenshot from app above):

let occlusion = OcclusionMaterial()
clonedEntity.model?.materials[index] = occlusion

Is it possible to somehow hide parts of 3D model? Or do I have to several models and when I want to change filling for example I must change whole model? Or should I somehow composite one object from multiple models (for example filling and rest of fence)? Thanks for any advice.

Answer 1

The most robust way is to create a component USDZ model (containing separate parts) and then use .isEnabled instance property in RealityKit 2.0 to turn any part On or Off.

import UIKit
import RealityKit

class ViewController: UIViewController {

    @IBOutlet var arView: ARView!
    let shelf = try! ModelEntity.load(named: "Shelf")
    var counter: Int = 0

    override func touchesBegan(_ touches: Set<UITouch>, 
                              with event: UIEvent?) {
        self.counter += 1

        let metal = shelf.children[0].children[0].children[0]
                         .children[0].children[0].children[0] as! ModelEntity
        let wood = shelf.children[0].children[0].children[0]
                        .children[0].children[0].children[1] as! ModelEntity

        if counter % 3 == 1 {
            metal.isEnabled = false
            wood.isEnabled = true
        } else if counter % 3 == 2 {
            metal.isEnabled = true
            wood.isEnabled = false
        } else if counter % 3 == 0 {
            metal.isEnabled = true
            wood.isEnabled = true
        }
    }
    override func viewDidLoad() {
        super.viewDidLoad()
        let anchor = AnchorEntity()
        anchor.addChild(shelf)
        arView.scene.anchors.append(anchor)
    }
}

If you do not like using .children[i] chaining, look at this answer,