Reality Composer Pro 3

import SwiftUI
import RealityKit

// MARK: - visionOS app entry point showing a RCP3-authored scene

@main
struct AlchemyLabApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }

        ImmersiveSpace(id: "AlchemyLab") {
            AlchemyLabView()
        }
    }
}

struct ContentView: View {
    @Environment(\.openImmersiveSpace) private var openImmersiveSpace

    var body: some View {
        Button("Open Alchemy Lab") {
            Task { await openImmersiveSpace(id: "AlchemyLab") }
        }
        .padding()
    }
}

// MARK: - Immersive view that loads the RCP3 scene bundle

struct AlchemyLabView: View {
    var body: some View {
        RealityView { content in
            // Load the .usda scene exported / authored in Reality Composer Pro 3.
            // The scene already contains a LightmapComponent baked in RCP3.
            guard let scene = try? await Entity(named: "AlchemyArea",
                                               in: Bundle.main) else {
                return
            }

            content.add(scene)

            // Locate the two prototype instances authored in RCP3.
            if let magicEffect = scene.findEntity(named: "Magic Effect"),
               let brewingEffect = scene.findEntity(named: "Brewing Effect") {

                // Override the point-light color on the Magic Effect instance
                // at runtime — mirrors the per-instance override workflow in RCP3.
                overrideLightColor(on: magicEffect,
                                   color: .init(red: 0.4, green: 0.0, blue: 1.0, alpha: 1.0))

                // Override the Brewing Effect instance with a warmer tone.
                overrideLightColor(on: brewingEffect,
                                   color: .init(red: 1.0, green: 0.5, blue: 0.0, alpha: 1.0))
            }
        }
    }

    // MARK: - Helper: override PointLightComponent on an RCP3 prototype instance

    private func overrideLightColor(on entity: Entity,
                                    color: UIColor) {
        // Walk child hierarchy to find the glow entity that holds the light.
        guard let glowEntity = entity.findEntity(named: "Glow") else { return }

        // Read existing component, mutate, write back — standard RealityKit pattern.
        var light = glowEntity.components[PointLightComponent.self]
                   ?? PointLightComponent()
        light.color     = color
        light.intensity = 800          // lumens
        light.attenuationRadius = 0.4  // metres
        glowEntity.components.set(light)
    }
}