Setting massProperties on a USDZ-loaded entity corrupts its transform (position/scale → NaN) Category: RealityKit / visionOS Environment: visionOS 26.x Summary: Modifying PhysicsBodyComponent.massProperties at runtime on an entity loaded from a .usdz file silently corrupts the entity's transform. The translation and scale components become NaN, while rotation remains valid. The corruption occurs during the next RealityKit scene update cycle (e.g., during an await suspension on the main actor). Steps to Reproduce: Author a .usda file with a RigidBody component including valid m_mass and m_inertia values Load the entity at runtime via Entity(named: "MyEntity.usdz", in: bundle) Read the existing PhysicsBodyComponent, modify massProperties, and set it back: if var physics = entity.components[PhysicsBodyComponent.self] { physics.massProperties = .init( mass: 1.944, inertia: SIMD3<Float>(0.013, 0.026, 0.016), centerOfMass: (position: .zero, orientation: .init()) ) entity.components.set(physics) } Add the entity to the scene Perform any await call (e.g., TextureResource(contentsOf:)) that yields to the main actor, allowing a RealityKit scene update to run Expected: The entity retains its position and scale with the updated mass/inertia values. Actual: The entity's transform becomes corrupted: Transform( scale: SIMD3<Float>(nan, nan, nan), rotation: simd_quatf(real: 1.0, imag: SIMD3<Float>(0.0, 0.0, 0.0)), // ← fine translation: SIMD3<Float>(-nan, -nan, -nan) ) Additional findings from investigation: The entity's physics mode does not matter — corruption occurs even when the entity is .kinematic Creating a new PhysicsBodyComponent(...) and replacing the existing one also triggers the bug Modifying other properties on the same component (linearDamping, angularDamping, material, mode) does not cause corruption — only massProperties triggers it The parent entity's transform remains valid The computed mass/inertia values themselves are valid (finite, positive) The corruption is silent — no error, no warning, no crash from RealityKit itself Workaround: Author mass and inertia values directly in the .usda file and do not modify massProperties at runtime: def RealityKitStruct "massFrame" { float3 m_inertia = (0.02, 0.02, 0.038) float m_mass = 2.5 def RealityKitStruct "m_pose" { } } Other PhysicsBodyComponent properties (damping, material, mode) can safely be modified at runtime.

swift test (SwiftPM CLI) fails to decode RealityKit custom components from USD files, even though entity.components.has(MyComponent.self) returns true. Typed access via entity.components[MyComponent.self] returns nil. This forces projects that use RealityKit custom components to use xcodebuild test exclusively. Minimal repro: github.com/mesqueeb/swiftpm-realitykit-custom-component-repro Repro steps git clone https://github.com/mesqueeb/swiftpm-realitykit-custom-component-repro cd swiftpm-realitykit-custom-component-repro swift test --filter componentsPresentButNotDecodableInSwiftTest Observed ✅ entity.components.has(ReproComponent.self) returns true ❌ entity.components[ReproComponent.self] returns nil Expected If has(...) returns true for a registered custom component, typed lookup should decode and return non-nil. Notes Running the same test via xcodebuild test works correctly The component is properly registered and the USDA file correctly references it This affects any project that relies on custom RealityKit components in tests — there is no swift test workaround Feedback ID: FB22099519 Environment: macOS 15.5, Xcode 16.4, Swift 6.1

I'm converting my game from SceneKit to RealityKit. It has a SpriteKit overlay that according to Explore advanced rendering with RealityKit 2 I can add with the code below. The code runs fine if the SKScene only contains a SKSpriteNode (see the commented out line), but when I add a SKShapeNode with a fillColor instead, the app crashes with this error: -[MTLDebugRenderCommandEncoder validateCommonDrawErrors:]:5970: failed assertion `Draw Errors Validation MTLDepthStencilDescriptor uses frontFaceStencil but MTLRenderPassDescriptor has a nil stencilAttachment texture MTLDepthStencilDescriptor uses backFaceStencil but MTLRenderPassDescriptor has a nil stencilAttachment texture ' I don't know enough about low-level graphics and stencils yet to figure out a quick solution, so I would appreciate if anyone could share an easy fix or explanation of what's wrong. Thanks! class ViewController: NSViewController { var device: MTLDevice! var renderer: SKRenderer! override func loadView() { let arView = ARView(frame: NSScreen.main!.frame) view = arView arView.renderCallbacks.prepareWithDevice = { [weak self] device in guard let self = self else { return } self.device = device renderer = SKRenderer(device: MTLCreateSystemDefaultDevice()!) let scene = SKScene() let shape = SKShapeNode(rectOf: CGSize(width: 10, height: 10)) shape.fillColor = .red scene.addChild(shape) // scene.addChild(SKSpriteNode(color: .red, size: CGSize(width: 10, height: 10))) renderer.scene = scene } arView.renderCallbacks.postProcess = { [weak self] context in guard let self = self else { return } let encoder = context.commandBuffer.makeBlitCommandEncoder() encoder?.copy(from: context.sourceColorTexture, to: context.targetColorTexture) encoder?.endEncoding() renderer.update(atTime: context.time) let descriptor = MTLRenderPassDescriptor() descriptor.colorAttachments[0].loadAction = .load descriptor.colorAttachments[0].storeAction = .store descriptor.colorAttachments[0].texture = context.targetColorTexture renderer.render(withViewport: CGRect(x: 0, y: 0, width: context.targetColorTexture.width, height: context.targetColorTexture.height), commandBuffer: context.commandBuffer, renderPassDescriptor: descriptor) } } }

Problem Summary After upgrading to iOS 26.1 and 26.2, I'm experiencing a particle positioning bug in RealityKit where ParticleEmitterComponent particles render at an incorrect offset relative to their parent entity. This behavior does not occur on iOS 18.6.2 or earlier versions, suggesting a regression introduced in the newer OS builds. Environment Details Operating System: iOS 26.1 & iOS 26.2 Framework: RealityKit Xcode Version: 16.2 (16C5032a) Expected vs. Actual Behavior Expected: Particles should render at the position of the entity to which the ParticleEmitterComponent is attached, matching the behavior on iOS 18.6.2 and earlier. Actual: Particles appear away from their parent entity, creating a visual misalignment that breaks the intended AR experience. Steps to Reproduce Create or open an AR application with RealityKit that uses particle components Attach a ParticleEmitterComponent to an entity via a custom system Run the application on iOS 26.1 or iOS 26.2 Observe that particles render at an offset position away from the entity Minimal Code Example Here's the setup from my test case: Custom Component & System: struct SparkleComponent4: Component {} class SparkleSystem4: System { static let query = EntityQuery(where: .has(SparkleComponent4.self)) required init(scene: Scene) {} func update(context: SceneUpdateContext) { for entity in context.scene.performQuery(Self.query) { // Only add once if entity.components.has(ParticleEmitterComponent.self) { continue } var newEmitter = ParticleEmitterComponent() newEmitter.mainEmitter.color = .constant(.single(.red)) entity.components.set(newEmitter) } } } AR Setup: let material = SimpleMaterial(color: .gray, roughness: 0.15, isMetallic: true) let model = Entity() model.components.set(ModelComponent(mesh: boxMesh, materials: [material])) model.components.set(SparkleComponent4()) model.position = [0, 0.05, 0] model.name = "MyCube" let anchor = AnchorEntity(.plane(.horizontal, classification: .any, minimumBounds: [0.2, 0.2])) anchor.addChild(model) arView.scene.addAnchor(anchor) Questions for the Community Has anyone else encountered this particle positioning issue after updating to iOS 26.1/26.2? Are there known workarounds or configuration changes to ParticleEmitterComponent that restore correct positioning? Is this a confirmed bug, or could there be a change in coordinate system handling or transform inheritance that I'm missing? Additional Information I've already submitted this issue via Feedback Assistant(FB21346746)

I am new to RealityKit and Metal and I am building a RealityKit app that renders a procedural LowLevelMesh road. But the left and right side of the road is a complete green terrain mesh object and it doesn't look great. What I want is to add some rocks, tall trees and dence bushes (or weed) to make it look like the player is in the woods. But when I add many of those objects then the performance drains. What is the best approach to fill background empty spaces in the scene?

This started out as a plea for help, but in preparing this post I discovered the root cause. I'm posting it as a lesson learned in hopes it will help someone. I've spent a good chunk of March trying to get AR-mode working again in my unreleased game. I had it working with SceneKit and ARView 5 years ago, but since 2024 I've been converting the game to use RealityKit and RealityView on iOS, macOS, visionOS, and tvOS. I've been having no joy getting AR mode to work on iOS. I get the pass-through device video but the game content isn't anchored to the floor but rather anchored to the screen. I made a simple project with just a simple shape in the middle of a RealityView and an overlay with a SwiftUI toggle to go in and out of AR-mode. At first, my simple project worked, and I couldn't figure out what was different in the logic. Both projects used the same logic: func transitionToXR(_ content: inout RealityViewCameraContent) { content.remove(gameBoard.rootEntity) content.add(xrAnchor) content.camera = .spatialTracking Self.anchorStateChangedSubscription = content.subscribe(to: SceneEvents.AnchoredStateChanged.self) { event in if event.anchor == xrAnchor, event.isAnchored { xrAnchor.addChild(gameBoard.rootEntity) } } } Then I made an alternate version of my view, and reproduced the same "anchored to the screen not the floor" issue. I compared the code side-by-side and finally saw the difference! The one that didn't work, like my game, had a property 'cameraEntity' which is initialized with PerspectiveCamera(), position and look-at configured, then added as a child of the root entity. So, the simple fix was to remove 'cameraEntity' from the root entity before adding it to the detected AnchorEntity when going into AR-mode. Then when leaving AR-mode, I add back 'cameraEntity' as a child of the root entity and configure it again. So the lesson learned is: make sure there isn't a PerspectiveCamera in the tree of Entities added to an AnchorEntity with a .spatialTracking content camera. Apple: let me know if you think this is a bug or if I was being dumb. If a bug, I can use Feedback Assistant to report this. If I was being dumb, it wouldn't be the first time. :-)

Hi everybody, I have 2 separate animations run.usdz and walk.usdz animation files which are loaded perfectly in Reality Composer Pro and in the RealityKit application. I want to gradually increase the speed of my player by switching blending weight values from 0.0 (walking) to 1.0 (full speed running). let rabbit = await RabbitBuilder.loadWalkingRabbit() let runningRabbit = await RabbitBuilder.loadRunningRabbit() rabbit.scale = SIMD3(0.05, 0.05, 0.05) runningRabbit.scale = SIMD3(0.05, 0.05, 0.05) let walkAnimation = rabbit.availableAnimations let runAnimation = runningRabbit.availableAnimations RabbitWalker.walkAnim = walkAnimation.first! RabbitWalker.runAnim = runAnimation.first! guard let walk = RabbitWalker.walkAnim, let run = RabbitWalker.runAnim else { return } let blendTree = BlendTreeAnimation<JointTransforms>( BlendTreeBlendNode(sources: [ BlendTreeSourceNode(source: walk.definition, name: "walk", weight: .value(1 - weight)), BlendTreeSourceNode(source: run.definition, name: "run", weight: .value(weight)) ]), name: "rabbitLocomotion", repeatMode: .repeat, offset: TimeInterval(elapsed) ) // I have runtime error after executing this line: "Cannot add incompatible timeline type to blend tree." guard let resource = try? AnimationResource.generate(with: blendTree) else { return } entity.playAnimation(resource) static func loadWalkingRabbit() async -> Entity? { do { let scene = try await Entity(named: "Scene", in: realityKitEnvironmentBundle) guard let rabbit = await scene.findEntity(named: "RabbitWalk") else { return nil } await rabbit.removeFromParent() return rabbit } catch { return nil } } static func loadRunningRabbit() async -> Entity? { do { let scene = try await Entity(named: "Scene", in: realityKitEnvironmentBundle) guard let rabbit = await scene.findEntity(named: "RabbitRun") else { return nil } await rabbit.removeFromParent() return rabbit } catch { return nil } } But when I run this code I have this error; Cannot add incompatible timeline type to blend tree. By the way I have looked to developer's sample codes from here but I couldn't find any relevant BlendTreeAnimation sample which blends 2 animations. I would very happy if someone could direct me to a solution. Regards.

Hi there, I've discovered an issue with gesture handling in RealityKit when setting the camera’s fieldOfViewOrientation to horizontal. For instance, if I render a simple box at the center of the view with a collision shape that exactly matches its dimensions, the actual hit area behaves as if it's smaller than the box. Additionally, when attempting to drag the box away from the center, the hit area appears misaligned—offset slightly towards the center. Since the default fieldOfViewOrientation is vertical and everything works as expected in that mode, it seems that the gesture system might be assuming a vertical FOV. Given that the API allows setting it to horizontal, perhaps gestures should function correctly regardless of the orientation? Thank you!

I'm trying to scale the physics of a scene without changing the apparent size to avoid the low-speed zeroing-out of motion that the physics simulation does. I found a technique for using separate simulation and physics roots in the docs, but it relies on ARView, which VisionOS doesn't have. This seems more elegant than scaling absolutely everything with shared root -- any chance I'm just failing in my searches to find the equivalent functionality?

Hi everyone, I'm new to visionOS development. I'm trying to create a physics-based scene (with gravity) where users can pick up and move objects on a workbench. I am struggling with physics interactions during the drag gesture: Kinematic Mode: If I switch to .kinematic during the drag, the object moves smoothly but clips through other objects (no collisions). Dynamic Mode: I tried keeping it .dynamic and applying linear velocity toward the hand position, but the movement feels laggy and unresponsive. Hybrid Approach: I tried switching to .kinematic during DragGesture.onChange and back to .dynamic on collision, but this causes the entity to jitter/shake violently when touching other objects. Has anyone found a clean way to drag objects while maintaining solid collisions. Thanks for your help!

In ARKit there is ARGeoAnchor, which lets you anchor content using latitude and longitude so objects stay fixed to a real-world location. Is there an equivalent feature in RealityKit? I want to place points in the world and make sure they don't move or drift after placement. If RealityKit doesn't support this directly, what is the recommended approach?

I asked AI to build a realistic ocean shader for a VisionOS project using RealityKit. It gave a bunch instructions and asked me to connect large amount of nodes for the ShaderGraph in the Reality Composer Pro. I am just wondering if AI can help to generate the Metal shader code directly, or build the ShaderGraph nodes for me automatically.

I have a question I guess more for the Apple team. But why are there no totally 3D experiences for the Vision Pro lineup? I know they have given us tools to implement unity 3D games into iPhone and I guess you can also build it in RealityKit. But why at this moment are 3D games limited to just iPad and iPhone and can't you bring that into Vision Pro? Just to explain. When I say a totally 3D game, I mean games like Gorn. I mean the Vision Pro is definitely powerful enough, but it just feels limited to tabletop games and AR games. Is this something Apple is thinking about implementing?

I'm in the process of converting my SceneKit game to RealityKit. In SceneKit I used to be able to mark nodes as selected by setting SCNMaterial.emission with a custom color. I can do the same with PhysicallyBasedMaterial.emissiveColor, but I'd like to keep my entitities unaffected by the scene lights by using UnlitMaterial. In SceneKit I can set a category mask to indicate what light should affect what node, but there doesn't seem to be such a thing in RealityKit. So at the moment it seems like I have to choose between being able to mark an entity as selected, or having entities unaffected by lighting, but not both. Is there some effect or component I can use to mark entities as selected by applying some coloring regardless of the material used?

I want to fade objects in and out, and while setting an entity's OpacityComponent works, animating it doesn't seem to do anything. In the following code the second sphere should fade out, but it keeps its initial opacity. On the other hand, the animation that changes its transform works. What am I doing wrong? class ViewController: NSViewController { override func loadView() { let arView = ARView(frame: NSScreen.main!.frame) let anchor = AnchorEntity(.world(transform: matrix_identity_float4x4)) arView.scene.addAnchor(anchor) let sphere = ModelEntity(mesh: .generateSphere(radius: 0.5)) anchor.addChild(sphere) sphere.components.set(OpacityComponent(opacity: 0.1)) let sphere2 = ModelEntity(mesh: .generateSphere(radius: 0.5)) sphere2.position = .init(x: 0.2, y: 0, z: 0) anchor.addChild(sphere2) sphere2.components.set(OpacityComponent(opacity: 0.1)) sphere.playAnimation(try! AnimationResource.makeActionAnimation(for: FromToByAction(to: 0, timing: .linear), duration: 1, bindTarget: .opacity)) sphere.playAnimation(try! AnimationResource.makeActionAnimation(for: FromToByAction(to: Transform(translation: SIMD3(x: 0.1, y: 0, z: 0)), timing: .linear), duration: 1, bindTarget: .transform)) view = arView } }

I'm trying to convert my game from SceneKit to RealityKit. I noticed that even when the scene is static (nothing moves), RealityKit keeps using CPU. In SceneKit, CPU goes down to 0% with a static scene. With this simplest of games, RealityKit keeps using about 65% CPU: class ViewController: NSViewController { override func loadView() { view = ARView(frame: NSScreen.main!.frame) } } Is this expected or a bug? I created FB22125047.

I'm currently converting my game from SceneKit to RealityKit. What's the easiest way to run an animation in which every frame I want to run custom code, similar to SCNAction.customAction which accepts a callback that is called repeatedly until the action completes?

My procedural animation using IKRig occasionally jitters and throws this warning. It completely breaks immersion. getMoCapTask: Rig must be of type kCoreIKSolverTypePoseRetarget Any idea where to start looking or what could be causing this?

Hi. I'm trying to show 3D or AR content in multiple pages on an iOS app but I have found that if a RealityView is used earlier in a flow then future uses will never display the camera feed, even if those earlier uses do not use any spatial tracking. For example, in the following simplified view, the second page realityView will not display the camera feed even though the first view does not use it not start a tracking session. struct ContentView: View { var body: some View { NavigationStack { VStack { RealityView { content in content.camera = .virtual // showing model skipped for brevity } NavigationLink("Second Page") { RealityView { content in content.camera = .spatialTracking } } } } } } What is the way around this so that 3D content can be displayed in multiple places in the app without preventing AR content from working? I have also found the same problem when wrapping an ARView for use in SwiftUI.

We are developing a standalone AI avatar application for hospital reception kiosks using Mac mini (M2/M4). The app runs on SwiftUI + RealityKit, displays on a 75-inch monitor, and utilizes a USB-connected 4K camera and external sensors (LiDAR/mmWave). We have several technical concerns regarding the transition from iPadOS to macOS. Could you please provide insights on the following? ARKit/Vision Framework on macOS with External Camera On iPadOS, ARKit provides robust Face Tracking. On macOS with an external USB 4K camera: Can we achieve real-time face tracking (expression/gaze/depth) with Vision framework or ARKit comparable to iPadOS performance? Are there any specific limitations for accessing the Neural Engine via Vision framework for real-time 4K video analysis on macOS? Accessing External Hardware (LiDAR/Sensors) in Sandbox We plan to connect external LiDAR and mmWave sensors (e.g., Akara) via USB/Bluetooth. Is it feasible to communicate with these custom drivers/devices within the App Sandbox environment? Would DriverKit be required, or can we use standard serial communication APIs? On-Device LLM (MLX) & Thermals We intend to run a local LLM (e.g., Llama 3 using MLX framework) for offline conversation, alongside 3D rendering. With the M2/M4 Mac mini fan design, is there a risk of thermal throttling during 10+ hours of continuous operation (simultaneous CoreML + 3D rendering)? Is the Mac Studio recommended over the Mac mini for this thermal profile? Long-running Speech API Are there any known issues (memory leaks, API limits) when using Spherch framework and AVSpeechSynthesizer continuously for over 10 hours daily? 3D Display Output Are there any macOS constraints for rendering a SwiftUI window in a specific 3D format (e.g., Side-by-Side) and outputting it via HDMI to a 3D digital signage display (fixed refresh rate/resolution)? Thank you for your assistance.