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];
}];
