如何在Swift的SceneKit中为对象添加内边距

我在用SceneKit开发功能，但不管怎么设置，场景里的对象总会占满容器全部尺寸。我想通过添加四周内边距或动态调整对象大小来改变这个情况，目前用圆形图片测试，但对象始终适配SceneKit容器的尺寸。

SceneKitView代码 #

struct SceneKitView: UIViewRepresentable {
    let imageName: String

    func makeUIView(context: Context) -> SCNView {
        let sceneView = SCNView()
        sceneView.scene = makeScene()
        sceneView.allowsCameraControl = true
        sceneView.backgroundColor = UIColor.black
        return sceneView
    }

    func updateUIView(_ uiView: SCNView, context: Context) {
        // No dynamic updates needed yet
    }

    private func makeScene() -> SCNScene {
        let scene = SCNScene()
        let badgeNode = createBadgeNode(from: imageName)
        scene.rootNode.addChildNode(badgeNode)

        return scene
    }

    private func createBadgeNode(from imageName: String) -> SCNNode {
        guard let image = UIImage(named: imageName) else {
            fatalError("Image \(imageName) not found in assets.")
        }

        let screenWidth = UIScreen.main.bounds.width
        let screenHeight = UIScreen.main.bounds.height
        let horizontalPadding: CGFloat = 40 // <-- 无效果
        let maxBadgeWidth = screenWidth - horizontalPadding
        let aspectRatio = image.size.width / image.size.height

        let badgeWidth = Float(min(maxBadgeWidth, screenHeight * aspectRatio)) / 1000
        let badgeHeight = badgeWidth / Float(aspectRatio)

        let badgeGeometry = SCNPlane(width: CGFloat(badgeWidth), height: CGFloat(badgeHeight))
        let badgeMaterial = SCNMaterial()
        badgeMaterial.diffuse.contents = image
        badgeMaterial.isDoubleSided = true
        badgeGeometry.materials = [badgeMaterial]

        let badgeNode = SCNNode(geometry: badgeGeometry)
        badgeNode.position = SCNVector3(0, 0, 0)

        return badgeNode
    }
}

ContentView代码 #

struct ContentView: View {
    @State private var selectedImage: UIImage?
    var body: some View {
        VStack {
            SceneKitView(imageName: "Test1")
                .frame(width: 300, height: 300)
                //.edgesIgnoringSafeArea(.all)
        }
    }
}

尝试的调整及效果 #

• 默认代码效果：圆形图片完全填满300x300的容器
• 仅修改width参数：

  let badgeGeometry = SCNPlane(width: CGFloat(badgeWidth) + 0.1, height: CGFloat(badgeHeight))
  // 其余代码不变
  

  效果：图片高度被拉伸，形状变形
• 同时修改宽高参数：

  let badgeGeometry = SCNPlane(width: CGFloat(badgeWidth) + 0.1, height: CGFloat(badgeHeight) + 0.1)
  // 其余代码不变
  

  效果：图片整体被拉伸，严重扭曲
• 进一步调整height参数：

  let badgeGeometry = SCNPlane(width: CGFloat(badgeWidth) + 0.1, height: CGFloat(badgeHeight) + 0.5)
  // 其余代码不变
  

  效果：图片高度被过度拉伸，形状完全变形

解决方案 #

问题核心是SceneKit默认相机会自动适配场景内容，导致对象填满视图。以下是两种有效解决方式：

1. 手动设置相机参数，预留内边距

在makeScene()中添加自定义相机，通过控制相机位置和视野，让对象周围留出空间：

private func makeScene() -> SCNScene {
    let scene = SCNScene()
    let badgeNode = createBadgeNode(from: imageName)
    scene.rootNode.addChildNode(badgeNode)
    
    // 添加自定义相机
    let cameraNode = SCNNode()
    cameraNode.camera = SCNCamera()
    // 预留20%内边距，根据对象大小调整相机z轴位置
    let paddingFactor: Float = 1.2
    cameraNode.position = SCNVector3(0, 0, badgeNode.boundingSphere.radius * paddingFactor)
    // 让相机始终对准对象
    cameraNode.look(at: badgeNode.position)
    scene.rootNode.addChildNode(cameraNode)
    
    return scene
}

如果需要保留用户相机控制，可调整相机控制的限制范围；不需要则直接关闭allowsCameraControl。

2. 基于容器大小计算对象尺寸，保持比例

修正createBadgeNode的尺寸计算逻辑，以容器大小为基准，而非屏幕大小，同时严格保持图片原始比例：

// 新增containerSize参数，传递容器尺寸
private func createBadgeNode(from imageName: String, containerSize: CGSize) -> SCNNode {
    guard let image = UIImage(named: imageName) else {
        fatalError("Image \(imageName) not found in assets.")
    }
    
    let padding: CGFloat = 40
    let maxAvailableSize = CGSize(
        width: containerSize.width - padding*2,
        height: containerSize.height - padding*2
    )
    let aspectRatio = image.size.width / image.size.height
    
    // 计算符合比例的最大尺寸
    var badgeSize = CGSize()
    if image.size.width > image.size.height {
        badgeSize.width = maxAvailableSize.width
        badgeSize.height = maxAvailableSize.width / aspectRatio
    } else {
        badgeSize.height = maxAvailableSize.height
        badgeSize.width = maxAvailableSize.height * aspectRatio
    }
    
    // 转换为SceneKit合理单位（1单位≈1米，缩小尺寸适配场景）
    let scnWidth = Float(badgeSize.width) / 100
    let scnHeight = Float(badgeSize.height) / 100
    
    let badgeGeometry = SCNPlane(width: CGFloat(scnWidth), height: CGFloat(scnHeight))
    let badgeMaterial = SCNMaterial()
    badgeMaterial.diffuse.contents = image
    badgeMaterial.isDoubleSided = true
    badgeGeometry.materials = [badgeMaterial]
    
    let badgeNode = SCNNode(geometry: badgeGeometry)
    badgeNode.position = SCNVector3(0, 0, 0)
    
    return badgeNode
}

然后在makeScene和makeUIView中传递容器尺寸：

func makeUIView(context: Context) -> SCNView {
    let sceneView = SCNView()
    // 传递容器尺寸（也可通过参数动态传入）
    sceneView.scene = makeScene(containerSize: CGSize(width: 300, height: 300))
    sceneView.allowsCameraControl = true
    sceneView.backgroundColor = UIColor.black
    return sceneView
}

private func makeScene(containerSize: CGSize) -> SCNScene {
    let scene = SCNScene()
    let badgeNode = createBadgeNode(from: imageName, containerSize: containerSize)
    scene.rootNode.addChildNode(badgeNode)
    
    // 添加相机确保对象显示在视野内
    let cameraNode = SCNNode()
    cameraNode.camera = SCNCamera()
    cameraNode.position = SCNVector3(0, 0, badgeNode.boundingSphere.radius * 1.2)
    cameraNode.look(at: badgeNode.position)
    scene.rootNode.addChildNode(cameraNode)
    
    return scene
}

内容的提问来源于stack exchange，提问作者Yo19