How to output image without background? - ios

Question

I have a canvasImageView and draw something on it.
And I want to output an image just contain image region.
My output function is func saveBtnPressed(sender: UIButton).
Like following image, I want to output blue line region.
Have any idea to do this?
Thanks.
class CanvasViewController: UIViewController {
let canvasImageView: CanvasImageView = {
let ui = CanvasImageView()
ui.contentMode = .scaleAspectFit
ui.layer.backgroundColor = UIColor.clear.cgColor
ui.backgroundColor = UIColor.clear
ui.clipsToBounds = true
ui.isMultipleTouchEnabled = false
ui.isUserInteractionEnabled = true
return ui
}()
override func viewDidLoad() {
super.viewDidLoad()
self.title = "Color Yourself"
let save = UIBarButtonItem(barButtonSystemItem: .save, target: self, action: #selector(saveBtnPressed(sender:)))
let redo = UIBarButtonItem(barButtonSystemItem: .refresh, target: self, action: #selector(clearBtnPressed(sender:)))
let back = UIBarButtonItem(barButtonSystemItem: .stop, target: self, action: #selector(cancelBtnPressed(sender:)))
self.navigationItem.rightBarButtonItems = [save, redo]
self.navigationItem.leftBarButtonItem = back
self.setupView()
}
fileprivate func setupView() {
self.view.addSubview(canvasImageView)
if #available(iOS 11.0, *) {
self.canvasImageView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 0).isActive = true
} else {
self.canvasImageView.topAnchor.constraint(equalTo: topLayoutGuide.bottomAnchor, constant: 0).isActive = true
}
self.canvasImageView.snp.makeConstraints { (make) in
make.bottom.left.right.equalToSuperview()
}
}
//MARK: BUTTON ACTION
#objc func cancelBtnPressed(sender: UIBarButtonItem) {
self.dismiss(animated: false, completion: nil)
}
#objc func clearBtnPressed(sender: UIButton) {
canvasImageView.clearCanvas()
}
#objc func saveBtnPressed(sender: UIButton) {
//Here is output image.
UIGraphicsBeginImageContextWithOptions(self.canvasImageView.layer.bounds.size, true, 0.0)
self.canvasImageView.layer.render(in: UIGraphicsGetCurrentContext()!)
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
if let img = image {
UIImageWriteToSavedPhotosAlbum(img, self,#selector(image(_:didFinishSavingWithError:contextInfo:)), nil)
}
}
}
class CanvasImageView: UIImageView {
var lineColor = UIColor.red
var lineWidth: CGFloat = 10
var path: UIBezierPath?
var touchPoint: CGPoint!
var startingPoint: CGPoint!
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
self.startingPoint = touches.first?.location(in: self)
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
self.touchPoint = touches.first?.location(in: self)
self.path = UIBezierPath()
path?.move(to: startingPoint)
path?.addLine(to: touchPoint)
self.startingPoint = touchPoint
self.draw()
}
func draw() {
let shapeLayer = CAShapeLayer()
shapeLayer.path = path?.cgPath
shapeLayer.strokeColor = lineColor.cgColor
shapeLayer.lineWidth = lineWidth
shapeLayer.fillColor = UIColor.clear.cgColor
self.layer.addSublayer(shapeLayer)
self.setNeedsDisplay()
}
func clearCanvas() {
guard let drawPath = path else { return }
drawPath.removeAllPoints()
self.layer.sublayers = nil
self.setNeedsDisplay()
}
}