ios rectOfInterest AVCaptureMetadataOutput 忽略

Question

我在使用 AVCaptureMetadataOutput 和 rectOfInterest 时遇到了一些扫描限制问题。我已成功绘制 UIImage 以确保扫描区域正确。

但是，无论我做什么，只有当扫描项目位于屏幕的绝对中心时才有效。 它似乎忽略了我的直肠。

输出尺寸

Display size width: 414, height: 736
Percent size width: 0.724638, height: 0.407609
Crop search area: {{57, 218}, {300, 300}}
Crop search converted: {{0.29619565217391297, 0.13768115942028991},         {0.40760869565217395, 0.72463768115942029}}

这是绘制的黄色矩形

还有实际的方法。完整代码可以看这里https://github.com/fbacker/react-native-camera/blob/barcode-finder/ios/RCTCameraManager.m

- (void)startSession {
#if TARGET_IPHONE_SIMULATOR
  return;
#endif
  dispatch_async(self.sessionQueue, ^{
    if (self.presetCamera == AVCaptureDevicePositionUnspecified) {
      self.presetCamera = AVCaptureDevicePositionBack;
    }

    AVCaptureStillImageOutput *stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
    if ([self.session canAddOutput:stillImageOutput])
    {
      stillImageOutput.outputSettings = @{AVVideoCodecKey : AVVideoCodecJPEG};
      [self.session addOutput:stillImageOutput];
      self.stillImageOutput = stillImageOutput;
    }

    AVCaptureMovieFileOutput *movieFileOutput = [[AVCaptureMovieFileOutput alloc] init];
    if ([self.session canAddOutput:movieFileOutput])
    {
      [self.session addOutput:movieFileOutput];
      self.movieFileOutput = movieFileOutput;
    }

    AVCaptureMetadataOutput *metadataOutput = [[AVCaptureMetadataOutput alloc] init];
    CGRect scanBarcodeArea = CGRectMake(0, 0, 0, 0);
    if ([self.session canAddOutput:metadataOutput]) {

        [self.session addOutput:metadataOutput];
        [metadataOutput setMetadataObjectsDelegate:self queue:self.sessionQueue];
        [metadataOutput setMetadataObjectTypes:self.barCodeTypes];

        // we only want to scan specified area
        // NOTE; Seems we can only set the actual rect after session started, else it doesn't work
        if (self.barcodeFinderVisible) {

          NSNumber *imageWidth = [NSNumber numberWithFloat:self.previewLayer.frame.size.width];
          NSNumber *imageHeight = [NSNumber numberWithFloat:self.previewLayer.frame.size.height];
          double imageUseWidth = [imageWidth doubleValue];
          double imageUseHeight = [imageHeight doubleValue];
          double cropWidth = imageUseWidth * self.barcodeFinderPercentageSizeWidth;
          double cropHeight = imageUseHeight * self.barcodeFinderPercentageSizeHeight;
          double cropX = (imageUseWidth/2)-(cropWidth/2);
          double cropY = (imageUseHeight/2)-(cropHeight/2);
          CGRect scanLimit = CGRectMake(cropX, cropY, cropWidth, cropHeight);
          scanBarcodeArea = [_previewLayer metadataOutputRectOfInterestForRect:scanLimit];
          [metadataOutput setRectOfInterest:scanBarcodeArea];

        /* ############################
         DEBUG PURPOSE, get some values and draw yellow rect of actual scanning area
        */

          /*
          NSLog(@"Display size width: %@, height: %@", imageWidth, imageHeight);
          NSLog(@"Percent size width: %f, height: %f", self.barcodeFinderPercentageSizeWidth, self.barcodeFinderPercentageSizeHeight);
          NSLog(@"Crop search area: %@", NSStringFromCGRect(scanLimit));
          NSLog(@"Crop search converted: %@", NSStringFromCGRect(scanBarcodeArea));

          // PAUSE AND PLAY WILL DRAW YELLOW RECT, IF VALID, might appear auto as well. who knows.
          UIView *scanAreaView = [[UIView alloc] initWithFrame:scanLimit];
          scanAreaView.layer.borderColor = [UIColor yellowColor].CGColor;
          scanAreaView.layer.borderWidth = 4;
          [self.view addSubview:scanAreaView];
          */
        }
    }
    self.metadataOutput = metadataOutput;

    __weak RCTCameraManager *weakSelf = self;
    [self setRuntimeErrorHandlingObserver:[NSNotificationCenter.defaultCenter addObserverForName:AVCaptureSessionRuntimeErrorNotification object:self.session queue:nil usingBlock:^(NSNotification *note) {
      RCTCameraManager *strongSelf = weakSelf;
      dispatch_async(strongSelf.sessionQueue, ^{
        // Manually restarting the session since it must have been stopped due to an error.
        [strongSelf.session startRunning];
      });
    }]];

    [self.session startRunning];
  });
}

Answer 1

据我所知，

scanBarcodeArea = [_previewLayer metadataOutputRectOfInterestForRect:scanLimit];
      [metadataOutput setRectOfInterest:scanBarcodeArea];

此代码不能总是返回正确的矩形，有时返回 {{0,0},{0,0}}，因为我使用矩形导航，当我导航到相机屏幕，然后返回，并导航到相机再次，我得到了 {{0,0},{0,0}}，有人说 previewLayer 没有初始好。

即使我把这段代码放在

之后

[self.session startRunning];

当我第一次运行我的应用程序并第一次导航到相机屏幕时，也会得到 {{0,0},{0,0}}。

所以，我使用这些打击代码而不是 metadataOutputRectOfInterestForRect: 来计算矩形范围。

        NSNumber *imageWidth = [NSNumber numberWithFloat:self.previewLayer.frame.size.width];
        NSNumber *imageHeight = [NSNumber numberWithFloat:self.previewLayer.frame.size.height];

        double imageUseWidth = [imageWidth doubleValue];
        double imageUseHeight = [imageHeight doubleValue];
        double cropWidth = imageUseWidth * self.barcodeFinderPercentageSizeWidth;
        double cropHeight = imageUseHeight * self.barcodeFinderPercentageSizeHeight;
        double cropX = (imageUseWidth/2)-(cropWidth/2);
        double cropY = ((imageUseHeight)/2)-(cropHeight/2);

        // transform to camera coordinate
        double scanX = cropY / imageUseHeight;
        double scanY = cropX / imageUseWidth;
        double scanWidth = cropHeight / imageUseHeight;
        double scanHeight = cropWidth / imageUseWidth;

        CGRect rectOfInterest = CGRectMake(scanX, scanY, scanWidth, scanHeight);