AvCaptureVideoPreviewLayer metadataOutputRectOfInterest不适用于Ipad mini

Question

我使用 AVFoundation 创建了自己的扫描仪。我添加了一个感兴趣的矩形来限制扫描区域。它在屏幕上添加了一条红线，便于扫描。我在 IPhone 6s plus ， Iphone 6 ， Iphone 5 ， Ipad 2 gen上尝试过，甚至在< em> Ipod 并且在那里工作正常。 但是如果我在 Ipad Mini 上尝试1代和2代，它就不会打开相机。我也没有在日志中收到任何错误消息。这就是我添加红线以限制scannig区域的方法。

 _output.rectOfInterest = [_videoPreviewLayer metadataOutputRectOfInterestForRect:[self scanArea]];

- (CGRect) scanArea {

    float scanRectHeight = 4.0f;
    CGRect scanRect = CGRectMake(0, ((_screenHeight/2) - (scanRectHeight/2)), _screenWidth, scanRectHeight);
    NSLog(@"screenHeight/2: %f scanRectHeight/2: %f", _screenHeight/2, scanRectHeight/2);
    NSLog(@"screenHeight/2 - scanRectHeight/2: %f", ((_screenHeight/2)-(scanRectHeight/2)));
    NSLog(@"%@", NSStringFromCGRect(scanRect));
    UIView *scanAreaView = [[UIView alloc] initWithFrame:scanRect];
    UIColor *borderColor = [UIColor colorWithRed:1.0f green:0.0f blue:0.0f alpha:0.5f];
    scanAreaView.backgroundColor = borderColor;
    scanAreaView.layer.zPosition = 1;
    [self.view addSubview:scanAreaView];

    return scanRect;
}

-(void) setScreenSize {
    _screenHeight = [[UIScreen mainScreen] bounds].size.height;
    _screenWidth = [[UIScreen mainScreen] bounds].size.width;
    _screenScaleFactor = [UIScreen mainScreen].scale;
    if (_screenWidth > _screenHeight) {
        float tempHeight = _screenWidth;
        _screenWidth = _screenHeight;
        _screenHeight = tempHeight;
    }
}

- (BOOL) startReading {
    NSLog(@"startReading...");
    _captureSession = [[AVCaptureSession alloc] init];
    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

    NSError *error = nil;

    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];

    if(input) {
        [_captureSession addInput:input];
    } else {
        NSLog(@"error: %@", error);
        return NO;
    }

    _output = [[AVCaptureMetadataOutput alloc] init];
    if(_output)
    [_captureSession addOutput:_output];
    else
        NSLog(@"Could not add output!");

    [_output setMetadataObjectTypes:[self defaultMetaDataObjectTypes]];
    [_output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];

    UIInterfaceOrientation orientation = [[UIApplication sharedApplication] statusBarOrientation];
    _videoPreviewLayer = [AVCaptureVideoPreviewLayer layerWithSession:_captureSession];
    _videoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;

    if(UIInterfaceOrientationIsPortrait(orientation)) {
        _videoPreviewLayer.bounds = CGRectMake(0, 0, self.view.layer.bounds.size.width, self.view.layer.bounds.size.height);
        _videoPreviewLayer.position = CGPointMake(CGRectGetMidX(self.view.layer.bounds), CGRectGetMidY(self.view.layer.bounds));
    }
    else {
        _videoPreviewLayer.bounds = CGRectMake(0, 0, self.view.layer.bounds.size.height, self.view.layer.bounds.size.width);
        _videoPreviewLayer.position = CGPointMake(CGRectGetMidY(self.view.layer.bounds), CGRectGetMidX(self.view.layer.bounds));
    }

    [self initializeBoundingBox];

    [_captureSession startRunning];
    _output.rectOfInterest = [_videoPreviewLayer metadataOutputRectOfInterestForRect:[self scanArea]];

    NSLog(@"_output.rectOfInterest: %@", NSStringFromCGRect(_output.rectOfInterest));

    [self.view.layer addSublayer:_videoPreviewLayer];

    return YES;
}


-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection{
    NSLog(@"captureOutput...");
    for (AVMetadataObject *metadata in metadataObjects) {

        AVMetadataMachineReadableCodeObject *transformed = (AVMetadataMachineReadableCodeObject *)[_videoPreviewLayer transformedMetadataObjectForMetadataObject:metadata];

        _boundingBox.frame = transformed.bounds;
        _boundingBox.hidden = NO;

        NSArray *translatedCorners = [self translatePoints:transformed.corners fromView:self.view toView:_boundingBox];
        _boundingBox.corners = translatedCorners;

        _scannedString = transformed.stringValue;

        AudioServicesPlayAlertSound(kSystemSoundID_Vibrate);
        AudioServicesPlaySystemSound(kSystemSoundID_Vibrate );

        [self stopReading:nil];
    }
}

我记录了一些值以尝试查看差异。在我之前和之后给出 metadataOutputRectOfInterestForRect（）的矩形

- Iphone 6s plus

赋予 metadataOutputRectOfInterestForRect： {{0, 366}, {414, 4}}

的Rect

_output.rectOfInterest: {{0.49728260869565211, 0}, {0.0054347826086956763, 1}}

- Ipad 2 gen

赋予 metadataOutputRectOfInterestForRect： {{0, 510}, {768, 4}}

的Rect

_output.rectOfInterest: {{0.49853516, -2.9802322e-08}, {0.0029296875, 1}}

- Ipad mini 1 gen

赋予 metadataOutputRectOfInterestForRect： {{0, 510}, {768, 4}}

的Rect

_output.rectOfInterest: {{0.49853516, -2.9802322e-08}, {0.0029296875, 1}}

- iphone 6s

赋予 metadataOutputRectOfInterestForRect： {{0, 331.5}, {375, 4}}

的Rect

_output.rectOfInterest: {{0.49700149925037473, 0}, {0.0059970014992504206, 1}}

这个负值在开始时对我很突出，但我试图添加 fabsf（），它根本没有改变这个值。此值也出现在 Ipad 上，并且工作正常。

以下是相机未打开时扫描仪的屏幕截图：

所以我的问题是为什么它适用于所有这些设备接受 Ipad mini ，那里有一些我不知道的差异吗？

编辑：添加了更多代码段