二维码扫描 AVCaptureMetadataOutput setRectOfInterest详解

核心代码

    self.output = [[AVCaptureMetadataOutput alloc] init];
    [self.output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
    [self.output setRectOfInterest:({
        //竖屏时 二维码扫描框frame
        CGRect portraitScanningRect = QRCodeScanningRect;
        //横屏时 AVCaptureVideoPreviewLayer size
        CGSize landscapePreviewSize = CGSizeMake(CGRectGetHeight(videoPreviewFrame), CGRectGetWidth(videoPreviewFrame));
        //横屏时 二维码扫描狂frame
        CGRect landscapeScanningRect = ({
            CGRect rect;
            rect.origin = CGPointMake(portraitScanningRect.origin.y, landscapePreviewSize.height - CGRectGetMaxX(portraitScanningRect));
            rect.size = CGSizeMake(CGRectGetHeight(portraitScanningRect), CGRectGetWidth(portraitScanningRect));
            rect;
        });
        //预设视频输入高宽比
        CGFloat p1 = 1080./1920.;
        //AVCaptureVideoPreviewLayer 高宽比
        CGFloat p2 = landscapePreviewSize.height / landscapePreviewSize.width;
        /**
          屏幕高宽比 和 视频预设不相符时，需要做适当修正
         */
        CGRect rectOfInterest = ({
            CGRect rect;
            if (p1 < p2) {//屏幕宽度小于预设宽度，需对x进行修正
                CGFloat fitWidth = landscapePreviewSize.height / p1;//(当前实际高度对应的预设宽度)
                CGFloat xOffset = (fitWidth - landscapePreviewSize.width) / 2;
                rect.origin.x = (landscapeScanningRect.origin.x + xOffset)/landscapePreviewSize.width;
                rect.origin.y = landscapeScanningRect.origin.y / landscapePreviewSize.height;
            } else {//屏幕高度小于预设高度，需对y进行修正
                CGFloat fitHeight = landscapePreviewSize.width * p1;//(当前实际宽度对应的预设高度)
                CGFloat yOffset = (fitHeight - landscapePreviewSize.height) / 2;
                rect.origin.x = landscapeScanningRect.origin.x / landscapePreviewSize.width;
                rect.origin.y = (landscapeScanningRect.origin.y + yOffset)/landscapePreviewSize.height;
            }
            rect.size.width = CGRectGetWidth(landscapeScanningRect) / landscapePreviewSize.width;
            rect.size.height = CGRectGetHeight(landscapeScanningRect) / landscapePreviewSize.height;
            rect;
        });
        rectOfInterest;
    })];

注意以下几点：

1.setRectOfInterest 是相对于横屏而言的，此时坐标原点为竖屏时的右上角
2.setRectOfInterest 是扫描识别区域frame和AVCaptureVideoPreviewLayer 宽高的比值，而不是扫描识别区域frame本身

补充

后续发现，其实 AVCaptureVideoPreviewLayer类已经提供了便捷的计算RectOfInterest的方法

//未保证正确计算rectOfInterest 需要监听 AVCaptureInputPortFormatDescriptionDidChangeNotification通知
    __weak typeof(self) weakSelf = self;
    [[NSNotificationCenter defaultCenter] addObserverForName:AVCaptureInputPortFormatDescriptionDidChangeNotification object:nil queue:[NSOperationQueue currentQueue] usingBlock:^(NSNotification * _Nonnull note) {
        __strong typeof(weakSelf) strongSelf = weakSelf;
        strongSelf.output.rectOfInterest = [strongSelf.previewLayer metadataOutputRectOfInterestForRect:QRCodeScanningRect];
    }];

附加：

二维码扫描Demo https://github.com/Nomeqc/QRCodeScanningDemo