不久前我做了类似的事情，并在上面写了article。它是为VNRecognizeTextRequest 而不是VNDetectBarcodesRequest，但它是相似的。这就是我所做的：
- 连续执行
VNImageRequestHandler（完成后，重新开始）
- 将检测指示器视图存储在属性
var previousTrackingView: UIView?
- 每当请求处理程序完成时，将检测指示器设置为新矩形
- 使用Core Motion检测设备运动，并调整检测指示器的边框
结果如下：
如您所见，高度/y 坐标不是很准确。我的猜测是，Vision 只需要一条水平线来扫描条形码——就像杂货店里的激光扫描仪一样——所以它不会返回完整的高度。但这是一个不同的问题。
连续执行VNImageRequestHandler（一旦完成，重新开始）
为此，我创建了一个属性busyPerformingVisionRequest，只要这是错误的，我就会调用 Vision 请求。这是在 didOutput 函数内部，每当相机帧发生变化时都会调用该函数。
class ViewController: AVCaptureVideoDataOutputSampleBufferDelegate {
var busyPerformingVisionRequest = false
func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
guard let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else { return }
if busyPerformingVisionRequest == false {
lookForBarcodes(in: pixelBuffer) /// start the vision as many times as possible
}
}
}
将检测指示器视图存储在属性var previousTrackingView: UIView?中
下面是我的 Vision 处理程序，它在 Vision 请求完成时被调用。我首先将 busyPerformingVisionRequest 设置为 false，因此可以发出另一个 Vision 请求。然后我将边界框转换为屏幕坐标并调用self.drawTrackingView(at: convertedRect)。
func resultClassificationTracker(request: VNRequest?, error: Error?) {
busyPerformingVisionRequest = false
if let results = request?.results {
if let observation = results.first as? VNBarcodeObservation {
var x = observation.boundingBox.origin.x
var y = 1 - observation.boundingBox.origin.y
var height = CGFloat(0) /// ignore the bounding height
var width = observation.boundingBox.width
/// we're going to do some converting
let convertedOriginalWidthOfBigImage = aspectRatioWidthOverHeight * deviceSize.height
let offsetWidth = convertedOriginalWidthOfBigImage - deviceSize.width
/// The pixelbuffer that we got Vision to process is bigger then the device's screen, so we need to adjust it
let offHalf = offsetWidth / 2
width *= convertedOriginalWidthOfBigImage
height = width * (CGFloat(9) / CGFloat(16))
x *= convertedOriginalWidthOfBigImage
x -= offHalf
y *= deviceSize.height
y -= height
let convertedRect = CGRect(x: x, y: y, width: width, height: height)
DispatchQueue.main.async {
self.drawTrackingView(at: convertedRect)
}
}
}
}
每当请求处理程序完成时，将检测指示器动画到新的矩形
这是我的函数drawTrackingView。如果已经绘制了一个跟踪矩形视图，它会将其动画到新帧。如果没有，它只是将其添加为子视图。
func drawTrackingView(at rect: CGRect) {
if let previousTrackingView = previousTrackingView { /// already drawn one previously, just change the frame now
UIView.animate(withDuration: 0.8) {
previousTrackingView.frame = rect
}
} else { /// add it as a subview
let trackingView = UIView(frame: rect)
drawingView.addSubview(trackingView)
trackingView.backgroundColor = UIColor.blue.withAlphaComponent(0.2)
trackingView.layer.borderWidth = 3
trackingView.layer.borderColor = UIColor.blue.cgColor
previousTrackingView = trackingView
}
}
使用Core Motion检测设备运动，并调整检测指示器的边框
我首先存储几个与运动相关的属性。然后，在viewDidLoad 中，我开始动态更新。
-----ViewController.swift-----
/// motionManager will be what we'll use to get device motion
var motionManager = CMMotionManager()
/// this will be the "device’s true orientation in space" (Source: https://nshipster.com/cmdevicemotion/)
var initialAttitude: CMAttitude?
/// we'll later read these values to update the highlight's position
var motionX = Double(0) /// aka Roll
var motionY = Double(0) /// aka Pitch
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
/// viewDidLoad() is often too early to get the first initial attitude, so we use viewDidLayoutSubviews() instead
if let currentAttitude = motionManager.deviceMotion?.attitude {
/// we populate initialAttitude with the current attitude
initialAttitude = currentAttitude
}
}
override func viewDidLoad() {
super.viewDidLoad()
/// This is how often we will get device motion updates
/// 0.03 is more than often enough and is about the rate that the video frame changes
motionManager.deviceMotionUpdateInterval = 0.03
motionManager.startDeviceMotionUpdates(to: .main) {
[weak self] (data, error) in
guard let data = data, error == nil else {
return
}
/// This function will be called every 0.03 seconds
self?.updateTrackingFrames(attitude: data.attitude)
}
...
}
每隔 0.03 秒我会调用updateTrackingFrames，它会读取设备的新物理运动。这是为了减少抖动，例如当您的用户的手在颤抖时。
func updateTrackingFrames(attitude: CMAttitude) {
/// initialAttitude is an optional that points to the reference frame that the device started at
/// we set this when the device lays out it's subviews on the first launch
if let initAttitude = initialAttitude {
/// We can now translate the current attitude to the reference frame
attitude.multiply(byInverseOf: initAttitude)
/// Roll is the movement of the phone left and right, Pitch is forwards and backwards
let rollValue = attitude.roll.radiansToDegrees
let pitchValue = attitude.pitch.radiansToDegrees
/// This is a magic number, but for simplicity, we won't do any advanced trigonometry -- also, 3 works pretty well
let conversion = Double(3)
/// Here, we figure out how much the values changed by comparing against the previous values (motionX and motionY)
let differenceInX = (rollValue - motionX) * conversion
let differenceInY = (pitchValue - motionY) * conversion
/// Now we adjust the tracking view's position
if let previousTrackingView = previousTrackingView {
previousTrackingView.frame.origin.x += CGFloat(differenceInX)
previousTrackingView.frame.origin.y += CGFloat(differenceInY)
}
/// finally, we put the new attitude values into motionX and motionY so we can compare against them in 0.03 seconds (the next time this function is called)
motionX = rollValue
motionY = pitchValue
}
}
这个 Core Motion 实现不是很准确 - 我对调整跟踪指示器框架的乘数常数 (Double(3)) 进行了硬编码。但足以抵消小的抖动。
这是最终的回购：https://github.com/aheze/BarcodeScanner