RealityKit Soft Shadows & Physical Space Lighting

import RealityKit
import SwiftUI

struct SoftShadowDemoView: View {
    var body: some View {
        RealityView { content in
            // 1. Create the spotlight entity
            let spotLightEntity = Entity()

            // 2. Configure the SpotLightComponent
            var spotLight = SpotLightComponent(
                color: .white,
                intensity: 8000,
                innerAngleInDegrees: 20,
                outerAngleInDegrees: 45,
                attenuationRadius: 6.0
            )

            // 3. Configure soft shadows
            var shadow = SpotLightComponent.Shadow()
            // lightSize is the diameter in meters of the virtual light source.
            // Larger values produce a wider penumbra (softer shadow edges).
            shadow.lightSize = 0.7
            // Must be .medium or .high — .low forces hard shadows
            shadow.quality = .medium
            spotLight.shadow = shadow

            spotLightEntity.components.set(spotLight)

            // 4. Enable physical space lighting so the virtual spotlight
            //    illuminates real-world surfaces via the scene understanding mesh
            spotLightEntity.components.set(SpotLightComponent.SurroundingsLightComponent())

            // 5. Attach a projective texture (stars/nebulae image)
            if let starTexture = try? await TextureResource(named: "stars_nebulae") {
                let projectiveTexture = ProjectiveTextureComponent(
                    texture: starTexture
                )
                spotLightEntity.components.set(projectiveTexture)
            }

            // 6. Position the spotlight above the scene origin
            spotLightEntity.position = SIMD3<Float>(0, 1.5, 0)
            // Point downward/outward into the room
            spotLightEntity.orientation = simd_quatf(
                angle: -.pi / 4,
                axis: SIMD3<Float>(1, 0, 0)
            )

            content.add(spotLightEntity)

            // 7. Add a simple box entity to receive the soft shadow
            let boxMesh = MeshResource.generateBox(size: 0.3)
            let boxMaterial = SimpleMaterial(color: .systemTeal, isMetallic: false)
            let boxEntity = ModelEntity(mesh: boxMesh, materials: [boxMaterial])
            boxEntity.position = SIMD3<Float>(0, 0, -1.0)
            content.add(boxEntity)
        }
    }
}

#Preview {
    SoftShadowDemoView()
}