iOS自定义UIImagePickerController相机裁剪为圆形，方形，三角形？

Question

如何按照上面的图片为UIImagepickercontroller添加圆形，三角形，方形图像叠加
当用户按下相机按钮时，只能捕获圆形或三角形或方形内的图像。
我使用下面的代码，但它没有给出正确的结果。请看下面的图片。 这完全违背了我想要实现的目标。

-(void)openCamera {

    self.pickerController = [[UIImagePickerController alloc] init];
    self.pickerController.delegate = self;

    if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera])
    {

        [self.pickerController setSourceType:UIImagePickerControllerSourceTypeCamera];


    } else {

        UIAlertView *alertView = [[UIAlertView alloc]initWithTitle:@"Tatoo App" message:@"No Camera Available" delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil];

        [alertView show];

    }


    self.pickerController.allowsEditing = NO;
    self.pickerController.showsCameraControls = NO;


    // creating overlayView
    self.overlayView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.pickerController.view.frame.size.width-20, self.pickerController.view.frame.size.height)];
    // letting png transparency be
    self.overlayView .backgroundColor = [UIColor colorWithRed:0/255 green:0/255 blue:0/255 alpha:0.5];

    [self.overlayView .layer setOpaque:NO];
    self.overlayView .opaque = NO;

    /*
    UIView *circleView = [[UIView alloc]initWithFrame:CGRectMake(self.pickerController.view.frame.size.width/4, self.pickerController.view.frame.size.width/4, self.pickerController.view.frame.size.width/2, self.pickerController.view.frame.size.height/4)];

    circleView.backgroundColor = [UIColor greenColor];

    circleView.layer.cornerRadius = circleView.frame.size.width / 2;
    circleView.clipsToBounds = YES;


    [self.overlayView addSubview:circleView];
    [self.overlayView bringSubviewToFront:circleView];
    */
    CAShapeLayer *maskLayer = [CAShapeLayer layer];
    self.overlayView.layer.mask = maskLayer;
    self.maskLayer = maskLayer;

    // create shape layer for circle we'll draw on top of image (the boundary of the circle)

    CAShapeLayer *circleLayer = [CAShapeLayer layer];
    circleLayer.lineWidth = 3.0;
    circleLayer.fillColor = [[UIColor clearColor] CGColor];
    circleLayer.strokeColor = [[UIColor blackColor] CGColor];
    [self.overlayView.layer addSublayer:circleLayer];
    self.circleLayer = circleLayer;

    // create circle path

    [self updateCirclePathAtLocation:CGPointMake(self.view.bounds.size.width / 2.0, self.view.bounds.size.height / 2.0) radius:self.view.bounds.size.width * 0.30];

    CGFloat scale  = [[self.overlayView.window screen] scale];
    CGFloat radius = self.circleRadius * scale;
    CGPoint center = CGPointMake(self.circleCenter.x * scale, self.circleCenter.y * scale);

    CGRect frame = CGRectMake(center.x - radius,
                              center.y - radius,
                              radius * 2.0,
                              radius * 2.0);

    // temporarily remove the circleLayer

    //  CALayer *circleLayer = self.circleLayer;
    //   [self.circleLayer removeFromSuperlayer];

    // render the clipped image

    UIGraphicsBeginImageContextWithOptions(self.imageOverlay.frame.size, NO, 0.0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    if ([self.overlayView respondsToSelector:@selector(drawViewHierarchyInRect:afterScreenUpdates:)])
    {
        // if iOS 7, just draw it

        [self.overlayView drawViewHierarchyInRect:self.overlayView.bounds afterScreenUpdates:YES];
    }
    else
    {
        // if pre iOS 7, manually clip it

        CGContextAddArc(context, self.circleCenter.x, self.circleCenter.y, self.circleRadius, 0, M_PI * 2.0, YES);
        CGContextClip(context);
        [self.overlayView.layer renderInContext:context];
    }

    // capture the image and close the context

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    // add the circleLayer back

    [self.overlayView.layer addSublayer:circleLayer];

    // crop the image

    CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], frame);
    UIImage *croppedImage = [UIImage imageWithCGImage:imageRef];




  self.takePicture = [UIButton buttonWithType:UIButtonTypeRoundedRect];
     self.takePicture.frame = CGRectMake(80.0, self.pickerController.view.frame.size.height-100, 150.0, 30.0);
     self.takePicture.tag = 0;
    [ self.takePicture setTitle:@"Take" forState:UIControlStateNormal];
    [ self.takePicture addTarget:self action:@selector(takeSnapShot:) forControlEvents:UIControlEventTouchUpInside];
    [self.overlayView  addSubview: self.takePicture];

    self.pickerController.cameraOverlayView = self.overlayView;


    [self presentViewController:self.pickerController animated:YES completion:nil];

}