如何沿y轴制作cameraOverlayView (swift3)

import UIKit
import AVFoundation

class ViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    
    var captureSession: AVCaptureSession!
    var previewLayer: AVCaptureVideoPreviewLayer!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建捕捉会话
        captureSession = AVCaptureSession()
        
        // 获取后置摄像头设备
        guard let videoCaptureDevice = AVCaptureDevice.default(for: .video) else { return }
        
        do {
            // 创建输入流
            let videoInput = try AVCaptureDeviceInput(device: videoCaptureDevice)
            
            // 将输入流添加到会话
            if captureSession.canAddInput(videoInput) {
                captureSession.addInput(videoInput)
            } else {
                print("无法将输入流添加到会话")
                return
            }
            
            // 创建输出流
            let metadataOutput = AVCaptureMetadataOutput()
            
            // 将输出流添加到会话
            if captureSession.canAddOutput(metadataOutput) {
                captureSession.addOutput(metadataOutput)
                
                // 设置元数据类型为人脸识别
                metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
                metadataOutput.metadataObjectTypes = [.face]
            } else {
                print("无法将输出流添加到会话")
                return
            }
            
            // 创建预览图层
            previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
            previewLayer.frame = view.bounds
            previewLayer.videoGravity = .resizeAspectFill
            
            // 创建自定义图层
            let overlayLayer = CALayer()
            overlayLayer.frame = CGRect(x: 0, y: 0, width: view.bounds.width, height: view.bounds.height)
            overlayLayer.backgroundColor = UIColor.red.cgColor
            
            // 将自定义图层添加到预览图层的子图层中
            previewLayer.addSublayer(overlayLayer)
            
            // 将预览图层添加到视图中
            view.layer.addSublayer(previewLayer)
            
            // 开始捕捉会话
            captureSession.startRunning()
        } catch {
            print("创建输入流时出错：\(error.localizedDescription)")
        }
    }
    
    // 人脸识别回调方法
    func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
        // 处理人脸识别结果
    }
}