I am trying to achieve an effect such that the particles of a particle system are attracted to my hand entity. The hand entity is essentially an AnchorEntity that is tracking my right hand. let particleEmitterEntities = context.entities(matching: particleEmitterQuery, updatingSystemWhen: .rendering) for particleEmitterEntity in particleEmitterEntities { if var particleEmitter = particleEmitterEntity.components[ParticleEmitterComponent.self] { particleEmitter.mainEmitter.attractionCenter = rightHandEntity.position(relativeTo: nil) // trying to get the world space position of the hand // I also tried relative to particleEmitterEntity particleEmitterEntity.components[ParticleEmitterComponent.self] = particleEmitter } else { fatalError("Cannot find particle emitter") } } The particle attraction center doesn't seem to update Another issue I am noticing here that My particle system doesn't show the particle image a lot of times and just renders a placeholder square when I do this, when I comment this code out I get the right particle image. I believe this is due to the number of times this loop runs to update the position of the attraction center. What is the right way to do an effect where the particles are attracted to my hand.

In my Vision OS app I am using plane detection and I want to create planes that have physics I want to create an effect that my reality kit entities rest on real world detected planes. I was curious to see that the code below that I found in the Samples is the most efficient way of doing this. func processPlaneDetectionUpdates() async { for await anchorUpdate in planeTracking.anchorUpdates { let anchor = anchorUpdate.anchor if anchorUpdate.event == .removed { planeAnchors.removeValue(forKey: anchor.id) if let entity = planeEntities.removeValue(forKey: anchor.id) { entity.removeFromParent() } return } planeAnchors[anchor.id] = anchor let entity = Entity() entity.name = "Plane \(anchor.id)" entity.setTransformMatrix(anchor.originFromAnchorTransform, relativeTo: nil) // Generate a mesh for the plane (for occlusion). var meshResource: MeshResource? = nil do { let contents = MeshResource.Contents(planeGeometry: anchor.geometry) meshResource = try MeshResource.generate(from: contents) } catch { print("Failed to create a mesh resource for a plane anchor: \(error).") return } var material = UnlitMaterial(color: .red) material.blending = .transparent(opacity: .init(floatLiteral: 0)) if let meshResource { // Make this plane occlude virtual objects behind it. entity.components.set(ModelComponent(mesh: meshResource, materials: [material])) } // Generate a collision shape for the plane (for object placement and physics). var shape: ShapeResource? = nil do { let vertices = anchor.geometry.meshVertices.asSIMD3(ofType: Float.self) shape = try await ShapeResource.generateStaticMesh(positions: vertices, faceIndices: anchor.geometry.meshFaces.asUInt16Array()) } catch { print("Failed to create a static mesh for a plane anchor: \(error).") return } if let shape { entity.components.set(CollisionComponent(shapes: [shape], isStatic: true)) let physics = PhysicsBodyComponent(mode: .static) entity.components.set(physics) } let existingEntity = planeEntities[anchor.id] planeEntities[anchor.id] = entity contentEntity.addChild(entity) existingEntity?.removeFromParent() } } } extension MeshResource.Contents { init(planeGeometry: PlaneAnchor.Geometry) { self.init() self.instances = [MeshResource.Instance(id: "main", model: "model")] var part = MeshResource.Part(id: "part", materialIndex: 0) part.positions = MeshBuffers.Positions(planeGeometry.meshVertices.asSIMD3(ofType: Float.self)) part.triangleIndices = MeshBuffer(planeGeometry.meshFaces.asUInt32Array()) self.models = [MeshResource.Model(id: "model", parts: [part])] } } extension GeometrySource { func asArray<T>(ofType: T.Type) -> [T] { assert(MemoryLayout<T>.stride == stride, "Invalid stride \(MemoryLayout<T>.stride); expected \(stride)") return (0..<count).map { buffer.contents().advanced(by: offset + stride * Int($0)).assumingMemoryBound(to: T.self).pointee } } func asSIMD3<T>(ofType: T.Type) -> [SIMD3<T>] { asArray(ofType: (T, T, T).self).map { .init($0.0, $0.1, $0.2) } } subscript(_ index: Int32) -> (Float, Float, Float) { precondition(format == .float3, "This subscript operator can only be used on GeometrySource instances with format .float3") return buffer.contents().advanced(by: offset + (stride * Int(index))).assumingMemoryBound(to: (Float, Float, Float).self).pointee } } extension GeometryElement { subscript(_ index: Int) -> [Int32] { precondition(bytesPerIndex == MemoryLayout<Int32>.size, """ This subscript operator can only be used on GeometryElement instances with bytesPerIndex == \(MemoryLayout<Int32>.size). This GeometryElement has bytesPerIndex == \(bytesPerIndex) """ ) var data = [Int32]() data.reserveCapacity(primitive.indexCount) for indexOffset in 0 ..< primitive.indexCount { data.append(buffer .contents() .advanced(by: (Int(index) * primitive.indexCount + indexOffset) * MemoryLayout<Int32>.size) .assumingMemoryBound(to: Int32.self).pointee) } return data } func asInt32Array() -> [Int32] { var data = [Int32]() let totalNumberOfInt32 = count * primitive.indexCount data.reserveCapacity(totalNumberOfInt32) for indexOffset in 0 ..< totalNumberOfInt32 { data.append(buffer.contents().advanced(by: indexOffset * MemoryLayout<Int32>.size).assumingMemoryBound(to: Int32.self).pointee) } return data } func asUInt16Array() -> [UInt16] { asInt32Array().map { UInt16($0) } } public func asUInt32Array() -> [UInt32] { asInt32Array().map { UInt32($0) } } } I was also curious to know if I can do this without ARKit using SpatialTrackingSession. My understanding is that using SpatialTrackingSession in RealityKit I can only get the transforms of the AnchorEntities but it won't have geometry information to create the collision shapes.

I have a created an AnchorEntity for my index finger tip and then created a model entity (A sphere) as a child of it. This model entity has a collision component and a physics body component. I tried using dynamic and kinematic modes for the physics body component. I have created a plane from a cube that has collision component and a static physics body. I have subscribed to the CollisionEvents.Began on this plane. I have also stored it in a EventSubscription state variable. @State private var collisionSubscription: EventSubscription? The I subscribed as follows collisionSubscription = content.subscribe(to: CollisionEvents.Began.self, on: self.boxTopCollision, { collisionEvent in print("something collided with the box top") }) The collision event fires when I directly put the sphere above the plane and let gravity do the collision, but when the the sphere is the child of the anchor entity, the collision events don't happen. I tried adding collision and physics body component directly to the anchor entity and that doesn't work too. I created another sphere with a physics body and a collision component and input target component and manipulate it with a drag gesture. When the manipulation is happening and collide the plane and the sphere the events don't happen when my sphere is touching the plane, but when the gesture end and the sphere is in contact with the plane, the event gets fired. I am confused as to why this is happening. All I want to do is have a collider on my finger tip and want to detect the collision with this plane. How can I make this work? Is there some unstated rule somewhere as where a physics body is manipulated manually it cannot trigger collision events? For more context. I am using SpatialTrackingSession with the tracking configuration of .hand. I am successfully able to track the finger tip.

I am trying to make a shader for a disco ball lighting effect for my app. I want the light to reflect on the scene mesh. i was curious if anyone has pointers on how to do this in shader graph in reality composer pro or writing a surface shader. The effect rotates the dots as the ball spins. This is the effect in the apple clips that applies the effect to the scene mesh