Customize Cluster Marker. (Google Map on Swift)

gmapView.delegate = self
let images: [UIImage] = [UIImage(named: "close")!, UIImage(named: "close")!, UIImage(named: "close")!, UIImage(named: "close")!, UIImage(named: "close")!]
let iconGenerator = CustomClusterIconGenerator(buckets: [20, 50, 100, 200, 500], backgroundImages: images)
let renderer = CustomMClusterRenderer(mapView: gmapView, clusterIconGenerator: iconGenerator)
let algorithm = GMUNonHierarchicalDistanceBasedAlgorithm()
clusterManager = GMUClusterManager(map: gmapView, algorithm: algorithm, renderer: renderer)
clusterManager.setDelegate(self, mapDelegate: self)







// MARK: Custom Cluster Marker
class CustomClusterIconGenerator: GMUDefaultClusterIconGenerator {

    override func icon(forSize size: UInt) -> UIImage {
        let image = textToImage(drawText: String(size) as NSString, inImage: UIImage(named: "cross")!, font: UIFont.systemFont(ofSize: 12))
        return image
    }
    
    private func textToImage(drawText text: NSString, inImage image: UIImage, font: UIFont) -> UIImage {

        UIGraphicsBeginImageContext(image.size)
        image.draw(in: CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height))

        let textStyle = NSMutableParagraphStyle()
        textStyle.alignment = NSTextAlignment.center
        let textColor = UIColor.black
        let attributes=[
            NSAttributedString.Key.font: font,
            NSAttributedString.Key.paragraphStyle: textStyle,
            NSAttributedString.Key.foregroundColor: textColor]

        // vertically center (depending on font)
        let textH = font.lineHeight
        let textY = (image.size.height-textH)/2
        let textRect = CGRect(x: 0, y: textY, width: image.size.width, height: textH)
        text.draw(in: textRect.integral, withAttributes: attributes)
        let result = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return result!
    }

}