Realitykit / ArKit make a collision only between 2 objects - swiftui

Question

I have a ball and a cylinder. When i tap on the ball it moves in forward position. When the ball hits the cylinder they collide and the cylinder moves and changes color. Thats working fine.
I have 2 problems:
When i start the app the cylinder is constantly colliding and changes color immediately, so even when the ball is not near it. It looks like its colliding with something else.
The second thing is, there will be more cylinders in the scene, how can i make a collision event only between 2 objects. Lets say there are 2 cylinders in the scene how can ik set a filter or group.
import SwiftUI
import RealityKit
import ARKit
import FocusEntity
import Combine
struct ContentView : View {
var body: some View {
ARViewContainer()
}
}
struct ARViewContainer: UIViewRepresentable {
func makeUIView(context: Context) -> ARView {
let view = ARView()
let session = view.session
let config = ARWorldTrackingConfiguration()
config.planeDetection = .horizontal
session.run(config)
let coachingOverlay = ARCoachingOverlayView()
coachingOverlay.autoresizingMask = [.flexibleWidth, .flexibleHeight]
coachingOverlay.session = session
coachingOverlay.goal = .horizontalPlane
view.addSubview(coachingOverlay)
context.coordinator.view = view
session.delegate = context.coordinator
view.addGestureRecognizer(UITapGestureRecognizer(target: context.coordinator, action: #selector(Coordinator.handleTap)))
return view
}
func updateUIView(_ uiView: ARView, context: Context) {}
func makeCoordinator() -> Coordinator {
Coordinator()
}
//coordinator class
class Coordinator: NSObject,ARSessionDelegate {
weak var view: ARView?
var focusEntity: FocusEntity?
#Published var sceneIsPlaced:Bool = false //is de scene reeds geplaats na openen app
#Published var subscriptions: [AnyCancellable] = []
func session(_ session: ARSession, didAdd anchors: [ARAnchor]) {
guard let view = self.view else { return }
self.focusEntity = FocusEntity(on: view, style: .classic(color: .yellow))
}
//na tap op het scherm, wat te doen -> creeer locatie en plaats het object
#objc func handleTap(recognizer: UITapGestureRecognizer) {
guard let view = self.view, let focusEntity = self.focusEntity else { return }
//tap location van de tap gesture
let tapLocation = recognizer.location(in: self.view)
//Create Anchor
let anchor = AnchorEntity()
let importModel = try! Entity.load(named: "cilinder") //alle objects!
importModel.position = focusEntity.position
importModel.scale = SIMD3(repeating: 0.5)
//The cylinder
let kolomMiddleModel = importModel.findEntity(named: "cilinder")!.children[0] as! (ModelEntity & HasPhysicsBody & HasCollision)
let materialKolomMiddle = SimpleMaterial(color: .yellow, isMetallic: true)
kolomMiddleModel.model?.materials = [materialKolomMiddle]
kolomMiddleModel.generateCollisionShapes(recursive: false)
let physics = PhysicsBodyComponent(massProperties: .default, material: .default, mode: .dynamic)
kolomMiddleModel.components.set(physics)
//MAKE A BALL
let materialsBall = SimpleMaterial(color: .red, isMetallic: true)
let ballModel = ModelEntity(mesh: .generateSphere(radius: 0.1),
materials: [materialsBall])
as (Entity & HasPhysicsBody & HasCollision)
ballModel.position = [-0.1, -1.0,-0.1]
ballModel.generateCollisionShapes(recursive: true)
ballModel.name = "ballModel"
//LIGHTS --> let op voor de shadow moet de plane van occlusion material met dynamical lightning op tue
let directionalLight = DirectionalLight()
directionalLight.light.color = .white
directionalLight.light.intensity = 4000
directionalLight.light.isRealWorldProxy = true
directionalLight.shadow?.maximumDistance = 1.5
directionalLight.shadow?.depthBias = 7.0
directionalLight.orientation = simd_quatf(angle: .pi/1.5, axis: [0,1,0])
//maak een anchor voor het licht
let lightAnchor = AnchorEntity(world: [0, 0, 2.5])
lightAnchor.addChild(directionalLight)
//COLLISION EVENTS
DispatchQueue.main.async {
//collision of kolomModel
view.scene.subscribe(to: CollisionEvents.Began.self,
on: kolomMiddleModel) { _ in
print("Collision kolomModel detected!")
let material = SimpleMaterial(color: .red, isMetallic: true)
kolomMiddleModel.model?.materials = [material]
}.store(in: &self.subscriptions)
}
// view.installGestures(for: ballModel)
//
//PLACE SCENE IF NOT PLACED ALREADY
if !sceneIsPlaced {
//ADD MODELS TO ANCHOR
anchor.addChild(importModel)
anchor.addChild(ballModel)
anchor.addChild(lightAnchor)
view.scene.addAnchor(anchor)
sceneIsPlaced = true
//If the scene is already placed get the taplocation
}else{
if let locationEntity = view.entity(at: tapLocation) {
let entityTapped = locationEntity as! ModelEntity
//MAKE THE BALL GO FORWARD
print("entity tapped \(entityTapped)")
entityTapped.physicsBody = .init()
entityTapped.physicsBody?.mode = .kinematic
entityTapped.physicsMotion = PhysicsMotionComponent(linearVelocity: [0, 0, -0.5],
angularVelocity: [1, 3, 5])
}
}
}
}
}

Answer 1

Here is an example of two objects in RealityKit that can only collide with each other:
let sphere = ModelEntity(mesh: .generateSphere(radius: 0.1), materials: [SimpleMaterial()])
sphere.collision = CollisionComponent(shapes: [ShapeResource.generateSphere(radius: 0.1)])
sphere.collision?.filter = CollisionFilter(group: 1 << 2, categories: .default, mask: .default)
let cube = ModelEntity(mesh: .generateBox(size: [0.1, 0.1, 0.1]), materials: [SimpleMaterial()])
cube.collision = CollisionComponent(shapes: [ShapeResource.generateBox(size: [0.1, 0.1, 0.1])])
cube.collision?.filter = CollisionFilter(group: 1 << 1, categories: .default, mask: .default)
sphere.collision?.filter.collisionGroup = 1 << 1
cube.collision?.filter.collisionGroup = 1 << 2
arView.scene.addAnchor(sphere)
arView.scene.addAnchor(cube)
This code creates two objects: a sphere and a cube. Each object is given a CollisionComponent with a corresponding ShapeResource and CollisionFilter. The CollisionFilter for each object specifies that only objects in a different collisionGroup can collide with it. As a result, the sphere and cube can only collide with each other, not with other objects in the scene.
See more information about CollisionGroups here:
https://developer.apple.com/documentation/realitykit/collisionfilter