SceneKit – 根据物体与相机的距离来改变物体的不透明度

Question

我目前有 6 个球体，分别代表 x、-x、y、-y、z、-z 的方向，我想将每个 SCNSphere 的不透明度更改为 0，当它靠近我的相机并且满时远处时透明。

struct SceneKitView: UIViewRepresentable {
    var transparency: CGFloat = 0.5
    let sceneView = SCNView()
    
    func makeUIView(context: UIViewRepresentableContext<SceneKitView>) -> SCNView {
        
        sceneView.scene = SCNScene()
        sceneView.allowsCameraControl = true
        sceneView.autoenablesDefaultLighting = true
        sceneView.backgroundColor = UIColor.clear
        let radius: Float = 0.75
        
        createSphere(x: 0, y: radius, z: 0)
        createSphere(x: 0, y: -radius, z: 0)
        createSphere(x: radius, y: 0, z: 0)
        createSphere(x: -radius, y: 0, z: 0)
        createSphere(x: 0, y: 0, z: radius)
        createSphere(x: 0, y: 0, z: -radius)
        
        return sceneView
    }
    
    func updateUIView(_ uiView: SCNView, context: UIViewRepresentableContext<SceneKitView>) {
    }
    
    typealias UIViewType = SCNView
    
    func createSphere(x: Float, y: Float, z: Float) {
        let sphere = SCNSphere(radius: 0.1)
        sphere.firstMaterial?.diffuse.contents = UIColor.black
        sphere.firstMaterial?.transparency = transparency
        let spherenode = SCNNode(geometry: sphere)
        spherenode.position = SCNVector3(x: x, y: y, z: z)
        sceneView.scene?.rootNode.addChildNode(spherenode)
    }
}

Answer 1

在 SceneKit 中，要以 60 fps 的帧速率更新任何属性，您需要符合 SCNSceneRendererDelegate 协议并使用其名为 renderer(_:updateAtTime:) 的实例方法。

这是一个代码：

import SceneKit

class GameViewController: NSViewController, SCNSceneRendererDelegate {
    
    var scnView = SCNView()
    let sphereNode = SCNNode()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let scene = SCNScene()
        scnView = self.view as! SCNView
        scnView.delegate = self               // SCNSceneRendererDelegate
        scnView.scene = scene
        scnView.allowsCameraControl = true
        scnView.backgroundColor = NSColor.systemIndigo
        
        sphereNode.geometry = SCNSphere(radius: 1.0)
        scene.rootNode.addChildNode(sphereNode)
    }
    
    func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {

        DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {

            let sphereTransform = self.sphereNode.simdTransform.columns.3
            let cameraTransform = (self.scnView.pointOfView?.simdTransform.columns.3)!
        
            self.sphereNode.opacity = CGFloat((simd_distance(sphereTransform, 
                                                             cameraTransform) / 5.0) - 0.5)
        }
    }
}

或者您可以使用guard let 语句（UIKit 示例）查看可选绑定：

import SceneKit

class ViewController: UIViewController, SCNSceneRendererDelegate {
    
    @IBOutlet var scnView: SCNView!
    let sphereNode = SCNNode()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let scene = SCNScene()
        scnView.delegate = self               // SCNSceneRendererDelegate
        scnView.scene = scene
        scnView.allowsCameraControl = true
        scnView.backgroundColor = UIColor.systemIndigo
        
        sphereNode.geometry = SCNSphere(radius: 1.0)
        scene.rootNode.addChildNode(sphereNode)
    }

    func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {

        let sphereTransform = self.sphereNode.simdTransform.columns.3
    
        guard let cameraTransform = self.scnView.pointOfView?.simdTransform.columns.3
        else { return }
    
        self.sphereNode.opacity = CGFloat((simd_distance(sphereTransform,
                                                         cameraTransform) / 5.0) - 0.5)
    }
}