How can I load a scene from RC as a ModelEntity instead of a plain Entity?

Question

I am trying to load an Entity into my code from a scene in a Reality Composer project.

I am reaching out directly to the autogenerated .reality file because I do not want it placed automatically on the first plane it detects. I followed the documentation found in the article Taking Control of Scene Anchoring.

The sample project name is Experience and in there I have 2 scenes.

1. The autogenerated Box that comes automatically with a newly created project.
2. A Hexagon shaped imported USDZ file.

The code I use to load both as a ModelEntity is the following:

let url = Bundle.main.url(forResource: "Experience", 
                        withExtension: "reality")!
            .appending(path: "SceneName", directoryHint: .notDirectory)
        
let modelEntity = try! Entity.loadModel(contentsOf: url)

where SceneName is either the Box or the Hexagon.

Both fail to load.

If I instead use the following code they succeed, but they are loaded as an Entity not as a ModelEntity:

let modelEntity = try! Entity.load(contentsOf: url)

Is it possible to have objects loaded as a ModelEntity instead of an Entity? The method I am using so far, which I found in this post, is to traverse the children hierarchy, find the first ModelEntity, and copy its model and physics onto its parent, (which in my case works since I only have one object in the scene).

---

Edit: Even if I name the objects within the Scene and then try to get them with the findEntity(named:) method on the "root" Entity object found in the Scene, I again get an Entity and not a ModelEntity.

Answer 1

Reality Composer's .rcproject

In case you're using Reality Composer's Experience.rcproject file, try the following technique. Implement findEntity(named:) method and then use typecast as! operator to grab the desired model entity from RC scene.

import UIKit
import RealityKit

class ViewController: UIViewController {
    
    @IBOutlet var arView: ARView!
    typealias ModelPack = ModelEntity & HasPhysicsBody
    
    override func viewDidLoad() {
        super.viewDidLoad()

        let scene1 = try! Experience.loadBox()
        let scene2 = try! Experience.loadHexagon()
        
        print(scene1); print(scene2)
        
        let boxModel = scene1.findEntity(named: "simpBld_root") as! ModelPack
        let hexModel = scene2.findEntity(named: "simpBld_root") as! ModelPack
        boxModel.position.x = -0.075
        hexModel.position.x = 0.075
        
        let anchor = AnchorEntity()     // any RealityKit or ARKit anchor
        anchor.scale *= 3
        anchor.addChild(boxModel)
        anchor.addChild(hexModel)
        
        arView.scene.anchors.append(anchor)
    }
}

.reality file

Apple proprietary .reality format serves for a faster uploading time. Use the following approach to load .reality file into your 3D scene. Remember every RealityKit's scene is entities' hierarchy.

import UIKit
import RealityKit

class ViewController: UIViewController {
    
    @IBOutlet var arView: ARView!
    typealias ModelPack = ModelEntity & HasPhysicsBody
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let entity = try! Entity.load(named: "SomeScene.reality")
        print(entity)
        
        let boxModel = entity.findEntity(named: "simpBld_root") as! ModelPack
        
        let anchor = AnchorEntity(.face)
        anchor.addChild(boxModel)
        arView.scene.anchors.append(anchor)
    }
}