如何在ARKit中渲染新图像时清除内存？

import ARKit
import SceneKit

class ViewController: UIViewController, ARSCNViewDelegate {
    @IBOutlet var sceneView: ARSCNView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        sceneView.delegate = self
        sceneView.showsStatistics = true
    }
    
    func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {
        // 清除不再使用的纹理
        clearUnusedTextures()
        
        // 清除不再使用的节点
        clearUnusedNodes()
    }
    
    func clearUnusedTextures() {
        // 遍历所有纹理并释放不再使用的纹理
        for texture in TextureCache.shared.textures {
            if texture.referenceCount == 0 {
                texture.dispose()
            }
        }
        TextureCache.shared.textures.removeAll()
    }
    
    func clearUnusedNodes() {
        // 遍历场景中的所有节点并移除不再使用的节点
        for node in sceneView.scene.rootNode.childNodes {
            if !node.isHidden && node.geometry == nil {
                node.removeFromParentNode()
            }
        }
    }
}

class TextureCache {
    static let shared = TextureCache()
    var textures: [SCNMaterial] = []
    
    private init() {}
    
    func addTexture(_ texture: SCNMaterial) {
        textures.append(texture)
    }
    
    func dispose() {
        for texture in textures {
            texture.diffuse.contents = nil
            texture.normal.contents = nil
            texture.specular.contents = nil
        }
    }
}