如何在 iOS 中使用 Objective C 扫描 AVCaptureVideoPreviewLayer 特定区域的条码？

Question

我正在尝试使用 Objective C 中的 AVFoundation 在我的 iPhone 应用程序中实现条形码扫描仪。条形码扫描部分工作正常，但问题是当前预览显示在设备的整个屏幕上，我希望扫描仪预览显示在设备的特定区域，需要改变背景的亮度区域（请参考下面的截图）。

如何放置AVCaptureVideoPreviewLayer 的特定区域以获取带角的条形扫描仪结果？

Answer 1

我的 pj 中有一个示例，它在 Swift 中，但我想你可以很好地转换它，根据需要调整代码，55 是每一行的长度

要创建角落，也许可以这样做，scanRectView 是兴趣矩形：

func createFrame() -> CAShapeLayer {
    let height: CGFloat = self.scanRectView.frame.size.height
    let width: CGFloat = self.scanRectView.frame.size.width
    let path = UIBezierPath()
    path.move(to: CGPoint(x: 5, y: 50))
    path.addLine(to: CGPoint(x: 5, y: 5))
    path.addLine(to: CGPoint(x: 50, y: 5))
    path.move(to: CGPoint(x: height - 55, y: 5))
    path.addLine(to: CGPoint(x: height - 5, y: 5))
    path.addLine(to: CGPoint(x: height - 5, y: 55))
    path.move(to: CGPoint(x: 5, y: width - 55))
    path.addLine(to: CGPoint(x: 5, y: width - 5))
    path.addLine(to: CGPoint(x: 55, y: width - 5))
    path.move(to: CGPoint(x: width - 55, y: height - 5))
    path.addLine(to: CGPoint(x: width - 5, y: height - 5))
    path.addLine(to: CGPoint(x: width - 5, y: height - 55))
    let shape = CAShapeLayer()
    shape.path = path.cgPath
    shape.strokeColor = UIColor.white.cgColor
    shape.lineWidth = 5
    shape.fillColor = UIColor.clear.cgColor
    return shape
}

目标 C 代码：

    CGFloat height = baseScannerView.frame.size.height+4;
    CGFloat width = baseScannerView.frame.size.width+4;

    UIBezierPath* path = [UIBezierPath bezierPath];

    [path moveToPoint:CGPointMake(1, 25)];
    [path addLineToPoint:CGPointMake(1, 1)];
    [path addLineToPoint:CGPointMake(25, 1)];

    [path moveToPoint:CGPointMake(width - 30, 1)];
    [path addLineToPoint:CGPointMake(width - 5, 1)];
    [path addLineToPoint:CGPointMake(width - 5, 25)];

    [path moveToPoint:CGPointMake(1, height - 30)];
    [path addLineToPoint:CGPointMake(1, height - 5)];
    [path addLineToPoint:CGPointMake(25, height - 5)];

    [path moveToPoint:CGPointMake(width - 30, height - 5)];
    [path addLineToPoint:CGPointMake(width - 5, height - 5)];
    [path addLineToPoint:CGPointMake(width - 5, height - 30)];

    CAShapeLayer *pathLayer = [CAShapeLayer layer];
    pathLayer.path = path.CGPath;
    pathLayer.strokeColor = [[UIColor redColor] CGColor];
    pathLayer.lineWidth = 5.0f;
    pathLayer.fillColor = nil;

    [self.scanRectView.layer addSublayer:pathLayer];

创建后，将其添加为self.scanRectView.layer.addSublayer(self.createFrame()) 中的viewWillAppear 或viewDidLayoutSubView

结果：

Answer 2

您可以根据自己的需要更改 AVCaptureVideoPreviewLayer 帧，像这样，这是示例，

AVCaptureVideoPreviewLayer *_CaptureLayer;
AVCaptureSession *_Capturesession;
_Capturesession = [[AVCaptureSession alloc] init];
_CaptureLayer = [AVCaptureVideoPreviewLayer layerWithSession: 
                                             _Capturesession];
_CaptureLayer = CGRectMake(self.view.frame.origin.x, 
                    self.view.frame.origin.y+100, 
                    self.view.frame.size.width, 
                    self.view.frame.size.height/2.5);

_CaptureLayer = AVLayerVideoGravityResizeAspectFill;
[self.view.layer addSublayer: _CaptureLayer];