从Uiview获取快照的最佳方法

Question

我正在通过拍摄快照（每秒30次）制作视频，我真的需要找到最好的方法，以最佳的性能在后台线程中获得快照。

我有两种方法在Uiview扩展程序中，

extension UIView {
 
    func snapshotInMain(view: UIView) -> UIImage {
        let render = UIGraphicsImageRenderer(size: view.bounds.size)
        let image = render.image { (context) in
            view.drawHierarchy(in: view.bounds, afterScreenUpdates: true)
        }
        return image
    }
    
    
    func snapShotInBackground(viewLayer: CALayer, viewBounds: CGRect) -> UIImage {
        let renderer = UIGraphicsImageRenderer(bounds: viewBounds)
        return renderer.image { rendererContext in
            viewLayer.render(in: rendererContext.cgContext)
        }
    }
}

第一个snapshotinmain在主线程中完全执行，它冻结了应用程序，但是屏幕截图本身更快地拍摄了，我从中获得了一个更平稳的视频

snapshotinbackground，该图层和边界是在主线程中计算的，但随后将在后台执行，但比在MAIN中执行的层较慢（首先 一）。 它的工作就像

DispatchQueue.main.async {
   let layer = self.selectedView.layer
   let bounds = self.selectedView.bounds
   DispatchQueue.global(qos: .background).async {
       let image = self.selectedView.snapShotInBackground(viewLayer: layer, viewBounds: bounds)
     }
}

我的工作确实对此非常不满意，我很呆在这里，真的需要帮助。请帮助我找到最好的选择。我的主要要求是 1-应用不应冻结 2-拍摄快照应该很快，我可以每秒钟30次。

谢谢你！期待您的帮助

Answer 1

您可以使用计时器在主线程上节拍快照。这是一个示例

    @objc
    private func beginTapped() {
        print("Start time \(Date.now)")
        frameCount = 0
        let timer = Timer.scheduledTimer(timeInterval: 0.03, target: self, selector: #selector(takeSnapshot), userInfo: nil, repeats: true)
        
        DispatchQueue.main.asyncAfter(deadline: .now() + 5, execute: {
            timer.invalidate()
            print("Finished at \(Date.now) with \(self.frameCount) frames captured")
        })
    }
    
    @objc
    private func takeSnapshot() {
        frameCount += 1
        let render = UIGraphicsImageRenderer(size: selectedView.bounds.size)
        let _ = render.image { (context) in
            selectedView.drawHierarchy(in: selectedView.bounds, afterScreenUpdates: true)
        }
    }

，该示例

Start time 2022-07-01 04:20:01 +0000
Finished at 2022-07-01 04:20:07 +0000 with 180 frames captured

将TimeInterval降低到0.01

Start time 2022-07-01 04:25:30 +0000
Finished at 2022-07-01 04:25:36 +0000 with 506 frames captured

在此期间的CPU使用率约为20％左右，并且该应用程序在我的琐碎示例中根本没有落后。

Answer 2

而不是采用快照我使用发电机是一个不错的选择，而是需要CPU，而不是导致UI/UX更平滑的内存

class VideoController:UIViewController {
    
    var timer = Timer()
    var secs:Double = 0
    
    var urls = [URL?]() {
        didSet {
            print(urls.count)
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        everSecond()
    }
    
    func everSecond() {
        // every second trigger
        timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(generate), userInfo: nil, repeats: true)
    }
    
    
    @objc
    func generate() {
        let url = Bundle.main.url(forResource: "Collection", withExtension: "mov")
        let videoAsset = AVAsset(url: url!)
        let duration = videoAsset.duration.seconds // duration of video
        if secs < duration {
            var timesArray:[NSValue] = []
            for i in 1...30 {
                let value:Double = Double(31 - i) // invers
                let t = CMTime(value: CMTimeValue(1 / value) + Int64(secs), timescale: 1) // getting time
                timesArray.append(NSValue(time: t)) // appending array
            }
            let generator = AVAssetImageGenerator(asset: videoAsset)
            generator.requestedTimeToleranceBefore = .zero
            //Optional generator.requestedTimeToleranceAfter = .zero //Optional
            generator.generateCGImagesAsynchronously(forTimes: timesArray) { requestedTime, image, actualTime, result, error in
                    if let img = image {
                        let m = UIImage(cgImage: img) // uiimage
                        let url = ViewController.saveImageInDocumentDirectory(image: m, fileName: "\(Date().timeStamp()).jpeg") //saved in documents with unique name
                        self.urls.append(url) // append url to array urls for save refrecnce
                    }
                
            }
            secs += 1
        } else {
            timer.invalidate()
        }
    }
    
    
    public static func saveImageInDocumentDirectory(image: UIImage, fileName: String) -> URL? {

            let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!;
            let fileURL = documentsUrl.appendingPathComponent(fileName)
            if let imageData = image.pngData() {
                try? imageData.write(to: fileURL, options: .atomic)
                return fileURL
            }
            return nil
        }

    public static func loadImageFromDocumentDirectory(fileName: String) -> UIImage? {

            let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!;
            let fileURL = documentsUrl.appendingPathComponent(fileName)
            do {
                let imageData = try Data(contentsOf: fileURL)
                return UIImage(data: imageData)
            } catch {}
            return nil
        }
}
extension Date {
    
    func timeStamp() -> String {
        let fomatter = DateFormatter()
        fomatter.dateFormat = "yyyy-MM-dd HH:mm:ss:SSS"
        return fomatter.string(from: self)
    }
}