如何在iOS的GoogleMaps中使用自定义标记进行标记聚类？

import GoogleMaps
import GoogleMapsUtils

class ViewController: UIViewController, GMSMapViewDelegate, GMUClusterManagerDelegate, GMUClusterRendererDelegate {
    
    var mapView: GMSMapView!
    var clusterManager: GMUClusterManager!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 初始化地图视图
        let camera = GMSCameraPosition.camera(withLatitude: 37.7749, longitude: -122.4194, zoom: 10)
        mapView = GMSMapView.map(withFrame: view.bounds, camera: camera)
        mapView.delegate = self
        view.addSubview(mapView)
        
        // 初始化标记聚类管理器
        let iconGenerator = GMUDefaultClusterIconGenerator()
        let algorithm = GMUNonHierarchicalDistanceBasedAlgorithm()
        let renderer = GMUDefaultClusterRenderer(mapView: mapView, clusterIconGenerator: iconGenerator)
        clusterManager = GMUClusterManager(map: mapView, algorithm: algorithm, renderer: renderer)
        clusterManager.setDelegate(self, mapDelegate: self)
        
        // 添加自定义标记
        let marker = GMSMarker()
        marker.position = CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4194)
        marker.title = "San Francisco"
        marker.icon = UIImage(named: "custom_marker_icon")
        clusterManager.add(marker)
        
        // 添加更多标记...
        
        // 聚合标记
        clusterManager.cluster()
    }
    
    // MARK: - GMSMapViewDelegate
    
    func mapView(_ mapView: GMSMapView, didTap marker: GMSMarker) -> Bool {
        // 处理标记点击事件
        return true
    }
    
    // MARK: - GMUClusterManagerDelegate
    
    func clusterManager(_ clusterManager: GMUClusterManager, didTap cluster: GMUCluster) -> Bool {
        // 处理聚合标记点击事件
        return true
    }
    
    // MARK: - GMUClusterRendererDelegate
    
    func renderer(_ renderer: GMUClusterRenderer, markerFor object: Any) -> GMSMarker? {
        if let clusterItem = object as? GMUClusterItem {
            let marker = GMSMarker()
            marker.position = clusterItem.position
            marker.title = clusterItem.title
            marker.icon = UIImage(named: "custom_marker_icon")
            return marker
        }
        return nil
    }
}