How to Spin and Add a Linear Force to an Entity Loaded from Reality Composer

RealityKit – How to add motion to a loaded ModelEntity from USDZ file?

Add to your code .generateCollisionShapes(recursive:) instance method for every participant (entity) that not only creates collision's shapes but also allows you to simulate physics.

import SwiftUI
import RealityKit

struct ARViewContainer: UIViewRepresentable {
    
    let boxx = ModelEntity(mesh: .generateBox(size: 0.5))
    let ball = ModelEntity(mesh: .generateSphere(radius: 0.25))
    let anchor = AnchorEntity()
    
    func makeUIView(context: Context) -> ARView {
        let arView = ARView(frame: .zero)
        // BALL
        ball.physicsBody = .init()
        ball.physicsMotion = .init()
        ball.physicsMotion?.linearVelocity = [10,0,0]
        ball.position.x = -3
        ball.generateCollisionShapes(recursive: true)
        anchor.addChild(ball)
        // BOX
        boxx.physicsBody = .init()
        boxx.physicsMotion = .init()
        boxx.physicsMotion?.linearVelocity = [0,2,0]
        boxx.generateCollisionShapes(recursive: true)
        anchor.addChild(boxx)
        // Anchor
        anchor.position.z = -3
        arView.scene.addAnchor(anchor)
        return arView
    }
    func updateUIView(_ uiView: ARView, context: Context) { }
}

...

struct ContentView : View {
    var body: some View {
        return ARViewContainer().edgesIgnoringSafeArea(.all)
    }
}

For more details, read THIS post.

RealityComposer – Glitch with Hide all on Scene Start

Try this to prevent a glimpse...

import UIKit
import RealityKit

class ViewController: UIViewController {
        
    @IBOutlet var arView: ARView!
    var box: ModelEntity!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let scene = try! Experience.loadScene()
        self.box = scene.cube!.children[0] as? ModelEntity
        self.box.isEnabled = false
        arView.scene.anchors.append(scene)
        
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
            self.box.isEnabled = true
        }
    }
}

In such a scenario glitching occurs only for sphere. Box object works fine.

How to Add Material to ModelEntity programatically in RealityKit?

Updated: June 14, 2022

RealityKit materials

There are 6 types of materials in RealityKit 2.0 and RealityFoundation at the moment:

• SimpleMaterial
• UnlitMaterial
• OcclusionMaterial (read this post to find out how to setup SceneKit occlusion shader)
• VideoMaterial (look at this post to find out how to setup it)
• PhysicallyBasedMaterial
• CustomMaterial

To apply these materials use the following logic:

import Cocoa
import RealityKit

class ViewController: NSViewController {        
    @IBOutlet var arView: ARView!
    
    override func awakeFromNib() {
        let box = try! Experience.loadBox()
        
        var simpleMat = SimpleMaterial()
        simpleMat.color = .init(tint: .blue, texture: nil)
        simpleMat.metallic = .init(floatLiteral: 0.7)
        simpleMat.roughness = .init(floatLiteral: 0.2)
        
        var pbr = PhysicallyBasedMaterial()
        pbr.baseColor = .init(tint: .green, texture: nil) 

        let mesh: MeshResource = .generateBox(width: 0.5, 
                                             height: 0.5, 
                                              depth: 0.5, 
                                       cornerRadius: 0.02, 
                                         splitFaces: true)

        let boxComponent = ModelComponent(mesh: mesh,
                                     materials: [simpleMat, pbr])

        box.steelBox?.children[0].components.set(boxComponent)
        box.steelBox?.orientation = Transform(pitch: .pi/4, 
                                                yaw: .pi/4, 
                                               roll: 0).rotation
        arView.scene.anchors.append(box)
    }
}

Read this post to find out how to load a texture for RealityKit's shaders.

How to create RealityKit's shaders similar to SceneKit's shaders

We know that in SceneKit there are 5 different shading models, so we can use RealityKit's SimpleMaterial, PhysicallyBasedMaterial and UnlitMaterial to generate all these five shaders that we've been accustomed to.

Let's see how it looks like:

SCNMaterial.LightingModel.blinn           – SimpleMaterial(color: . gray,
                                                        roughness: .float(0.5),
                                                       isMetallic: false)

SCNMaterial.LightingModel.lambert         – SimpleMaterial(color: . gray,
                                                        roughness: .float(1.0),
                                                       isMetallic: false)
  
SCNMaterial.LightingModel.phong           – SimpleMaterial(color: . gray,
                                                        roughness: .float(0.0),
                                                       isMetallic: false)

SCNMaterial.LightingModel.physicallyBased – PhysicallyBasedMaterial()

// all three shaders (`.constant`, `UnlitMaterial` and `VideoMaterial `) 
// don't depend on lighting
SCNMaterial.LightingModel.constant        – UnlitMaterial(color: .gray)
                                          – VideoMaterial(avPlayer: avPlayer)

Within RealityKit, how can I make the world without friction?

Apply a new Physics Material to your model entity.

For this use generate(friction:restitution:) type method:

static func generate(friction: Float = 0, 
                  restitution: Float = 0) -> PhysicsMaterialResource

where

/*   the coefficient of friction is in the range [0, infinity]   */

/*   and the coefficient of restitution is in the range [0, 1]   */

Here's a code:

arView.environment.background = .color(.darkGray)

let mesh = MeshResource.generateSphere(radius: 0.5)
let material = SimpleMaterial()
let model = ModelEntity(mesh: mesh,
                   materials: [material]) as (ModelEntity & HasPhysics)
    
let physicsResource: PhysicsMaterialResource = .generate(friction: 0, 
                                                      restitution: 0)
    
model.components[PhysicsBodyComponent] = PhysicsBodyComponent(
                                        shapes: [.generateSphere(radius: 0.51)],
                                          mass: 20,         // in kilograms
                                      material: physicsResource, 
                                          mode: .dynamic)

model.generateCollisionShapes(recursive: true)

let anchor = AnchorEntity()
anchor.addChild(model)
arView.scene.anchors.append(anchor)

P.S. Due to some imperfectness of physics engine in RealityKit, I suppose there's no possibility to create an eternal bouncing. Seemingly next RealityKit's update will fix physics engine imperfectness.

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