Day009

Place Objects Relative to the User

Goal: Add objects to the scene with coordinates relative to the user

3D models can be moved around within Volumes (windows with the Volumetric window style) and ImmersiveSpaces.

Volumes - Window

Add depth to your app with a 3D volume. Volumes are SwiftUI scenes that can showcase 3D content using RealityKit or Unity, creating experiences that are viewable from any angle in the Shared Space or an app’s Full Space.

Spaces - Scene

By default, apps launch into the Shared Space, where they exist side by side — much like multiple apps on a Mac desktop. Apps can use windows and volumes to show content, and the user can reposition these elements wherever they like. For a more immersive experience, an app can open a dedicated Full Space where only that app’s content will appear. Inside a Full Space, an app can use windows and volumes, create unbounded 3D content, open a portal to a different world, or even fully immerse people in an environment.

In a Volumetric Window

You can create a volumetric window by giving your window a volumetric style:

    var body: some Scene {
        WindowGroup {
            ContentView()
        }.windowStyle(.volumetric)
    }

Inside of this volume, you can position 3D objects a few ways using the [position](https://developer.apple.com/documentation/swiftui/view/position(x:y:) and [offset](https://developer.apple.com/documentation/swiftui/view/offset(z:) modifiers. These modifiers position the center of a view inside its parent's coordinate space. Inside the volume, the coordinate (0, 0, 0) refers to the left, upper, rear corner, respectively. In other words:

• Increasing the x value moves the object to the right
• Increasing the y value moves the object down
• Increasing the z value moves the object towards the user

    var body: some View {
        VStack {
            Model3D(named: "Scene", bundle: realityKitContentBundle)
                .position(x: 300,y: 500)
                .offset(z: 400)
            
            Text("Hello, world!")
        }
    }

Refer to this article on Making fine adjustments to a view's position for more info.

In a RealityView

It is more likely that you'll be handling 3D content inside of a RealityView. After creating a ModelEntity, you can change its position relative to its parent using its position property:

    var body: some View {
        RealityView{ content in
            let sphere : Entity = ModelEntity(
                mesh: .generateSphere(radius: 0.1),
                materials: [SimpleMaterial(color: .blue, isMetallic: false)]
            )
            
            sphere.position = SIMD3(0.4,0,0)
            content.add(sphere)
        }
    }

The coordinate system works the same in a RealityView with positive x being to the right, positive y being down, and positive z being towards the user.