UIImageView cropping - swift

Question

I am trying to allow users to crop an image. The problem is the cropped image is not the same as the view. Here are two screenshots to show what I mean.
pre crop screen:
!http://i58.tinypic.com/4rap9u.png
after crop
!http://i58.tinypic.com/2nrpjlj.png
Here is the code I use to create the new cropped image. The UIImageView is inside a UIScrollView to allow user to zoom and pan. Even when the image has not been zoomed it does not work correctly. Ideally I would like to allow the user to move the dashed square around the screen to select a portion of the image to crop, as well as zoom in/out.
func croppedImage() -> UIImage?
{
var drawRect: CGRect = CGRectZero
var cropRect : CGRect!
cropRect = photoFrameView?.frame
zoom = imgScroll.zoomScale
println(zoom)
drawRect.size = imgPreview.bounds.size
drawRect.origin.x = round(-cropRect.origin.x * zoom)
drawRect.origin.y = round(-cropRect.origin.y * zoom)
cropRect.size.width = round(cropRect.size.width*zoom)
cropRect.size.height = round(cropRect.size.height*zoom)
cropRect.origin.x = round(cropRect.origin.x)
cropRect.origin.y = round(cropRect.origin.y)
UIGraphicsBeginImageContextWithOptions(cropRect.size, false, UIScreen.mainScreen().scale)
self.imgPreview.image?.drawInRect(drawRect)
var result = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext();
return result
}
here is where I crop the image:
let cImg = croppedImage()!
UIImageWriteToSavedPhotosAlbum(cImg, nil, nil, nil);
imgPreview.image = cImg
self.imgPreview.contentMode = .ScaleAspectFit
Also here is the code for my UIView subclass(photoFrameView). Not sure if it is needed.
import UIKit
class mycropView: UIView {
var lastLocation:CGPoint = CGPointMake(0, 0)
override init(frame: CGRect) {
super.init(frame: frame)
// Initialization code
var panRecognizer = UIPanGestureRecognizer(target:self, action:"detectPan:")
self.gestureRecognizers = [panRecognizer]
self.addDashedBorder()
self.backgroundColor = UIColor.clearColor()
}
required init(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func detectPan(recognizer:UIPanGestureRecognizer) {
var translation = recognizer.translationInView(self.superview!)
self.center = CGPointMake(lastLocation.x + translation.x, lastLocation.y + translation.y)
}
override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
// Promote the touched view
self.superview?.bringSubviewToFront(self)
// Remember original location
lastLocation = self.center
}
override func hitTest(point: CGPoint, withEvent e: UIEvent?) -> UIView? {
if let result = super.hitTest(point, withEvent:e) {
println("hit inside")
return result
} else {
self.removeFromSuperview()
}
return nil
}
}
extension UIView {
func addDashedBorder() {
let color = UIColor.yellowColor().CGColor
let shapeLayer:CAShapeLayer = CAShapeLayer()
let frameSize = self.frame.size
let shapeRect = CGRect(x: 0, y: 0, width: frameSize.width, height: frameSize.height)
shapeLayer.bounds = shapeRect
shapeLayer.position = CGPoint(x: frameSize.width/2, y: frameSize.height/2)
shapeLayer.fillColor = UIColor.clearColor().CGColor
shapeLayer.strokeColor = color
shapeLayer.lineWidth = 2
shapeLayer.lineJoin = kCALineJoinRound
shapeLayer.lineDashPattern = [6,3]
shapeLayer.path = UIBezierPath(roundedRect: shapeRect, cornerRadius: 5).CGPath
self.layer.addSublayer(shapeLayer)
}
}