如何通过在RealityKit中以编程方式创建实体来添加地面阴影？

import RealityKit
import ARKit

let arView = ARView(frame: .zero)
let arConfig = ARWorldTrackingConfiguration()

let entity = ModelEntity(mesh: .generateBox(size: 1.0), materials: [SimpleMaterial(color: .red, isMetallic: true)])
entity.position = SIMD3(x: 0, y: 0, z: -2)

let shadowPlane = ShadowComponent(plane: .horizontal, size: CGSize(width: 1.0, height: 1.0), material: OcclusionMaterial(receivesDynamicLighting: false))
entity.components.set(shadowPlane)

let anchor = AnchorEntity()
anchor.addChild(entity)
arView.scene.addAnchor(anchor)