如何在RealityKit中为程序化创建的实体添加阴影？

我通过代码创建了一系列Box实体，在与桌面接触的位置存在轻微的环境光遮蔽，但未显示任何阴影——既没有地面阴影，也没有实体自身投射的阴影。不过使用Reality Composer创建的模型可以正常显示地面阴影。

系统环境：iOS 16.1.1

问题代码 #

let config = ARWorldTrackingConfiguration()
config.planeDetection = [.horizontal]
session.run(config, options: [])

let anchorEntity = AnchorEntity(plane: .horizontal)
scene.addAnchor(anchorEntity)

var material = PhysicallyBasedMaterial()
material.baseColor = PhysicallyBasedMaterial.BaseColor(tint: .white)

let box1 = ModelEntity(mesh: .generateBox(size: [0.05, 0.03, 0.05]), materials: [material])
box1.position = [0, 0.015, 0]
anchorEntity.addChild(box1)

let box2 = ModelEntity(mesh: .generateBox(size: [0.15, 0.03, 0.05]), materials: [material])
box2.position = [0.05, 0.045, 0]
anchorEntity.addChild(box2)

let box3 = ModelEntity(mesh: .generateBox(size: [0.01, 0.05, 0.01]), materials: [material])
box3.position = [0, 0.085, 0]
anchorEntity.addChild(box3)

RealityKit中代码生成的模型默认不会启用阴影投射与接收，而Reality Composer创建的模型会自动配置这些属性。你需要手动为每个ModelEntity设置以下属性：

• 启用阴影投射：设置castsShadow = true
• 启用阴影接收：设置receivesShadow = true

场景默认的环境光组件已支持阴影渲染，无需额外配置。

修改后的代码示例 #

let config = ARWorldTrackingConfiguration()
config.planeDetection = [.horizontal]
session.run(config, options: [])

let anchorEntity = AnchorEntity(plane: .horizontal)
scene.addAnchor(anchorEntity)

var material = PhysicallyBasedMaterial()
material.baseColor = PhysicallyBasedMaterial.BaseColor(tint: .white)

// 配置第一个Box
let box1 = ModelEntity(mesh: .generateBox(size: [0.05, 0.03, 0.05]), materials: [material])
box1.position = [0, 0.015, 0]
box1.castsShadow = true
box1.receivesShadow = true
anchorEntity.addChild(box1)

// 配置第二个Box
let box2 = ModelEntity(mesh: .generateBox(size: [0.15, 0.03, 0.05]), materials: [material])
box2.position = [0.05, 0.045, 0]
box2.castsShadow = true
box2.receivesShadow = true
anchorEntity.addChild(box2)

// 配置第三个Box
let box3 = ModelEntity(mesh: .generateBox(size: [0.01, 0.05, 0.01]), materials: [material])
box3.position = [0, 0.085, 0]
box3.castsShadow = true
box3.receivesShadow = true
anchorEntity.addChild(box3)

便捷封装（可选） #

如果需要批量创建带阴影的Box，可以封装工具方法：

func createShadowEnabledBox(size: SIMD3<Float>, material: PhysicallyBasedMaterial) -> ModelEntity {
    let box = ModelEntity(mesh: .generateBox(size: size), materials: [material])
    box.castsShadow = true
    box.receivesShadow = true
    return box
}

调用示例：

let box1 = createShadowEnabledBox(size: [0.05, 0.03, 0.05], material: material)
box1.position = [0, 0.015, 0]
anchorEntity.addChild(box1)

内容的提问来源于stack exchange，提问作者Mark Horgan