Erasing a stroke path with Quartz2D is deleting more than just the path - ios

Question

I'm trying to set an eraser tool for a drawing app. I've been following this tutorial for the basics, but the drawings happen in a white background so the deletion part is not covered (they draw in white color to delete)
I've been implementing a method to delete my drawings, and it works pretty well. I draw a circle, set the color and the blend mode to clear and set the path where I want to draw that circle. Then I get an image returned by the method UIGraphicsGetImageFromCurrentImageContext() that updates my current image, with the new drawing over it.
The drawn circle it's doing it's job and it deletes where it has been drawn. But the problem is the image begins to get deleted from the right to the left, covering all it's height, and this is certainly not set anywhere in my code.
I don't know if it's a bug.
I've tried everything and I can't get a new image from context without this new deletion line in the right. And the more I draw, the more the new line grows.
As you can see in the gif, it looks like I'm drawing in gray over a white background, but the white color is an image that has been filled with white color, and it's background color it's gray, so I'm deleting.
The code:
In a UIView (blue background) I initialize and add two white columns as subviews:
func addNewColumn(){
let column : Column = Column.init(frame: CGRect(x: self.frame.size.width*0.7, y: 0, width: self.frame.size.width*0.125, height: self.frame.size.height))
let column2 : Column = Column.init(frame: CGRect(x: self.frame.size.width*0.2, y: 0, width: self.frame.size.width*0.125, height: self.frame.size.height))
self.addSubview(column)
self.addSubview(column2)
}
The initialization of the column in its class:
import UIKit
class Column: UIImageView {
//Touches Positions
var firstPoint : CGPoint?
var lastPoint : CGPoint?
override init(frame: CGRect) {
super.init(frame: frame)
self.isUserInteractionEnabled = true
self.draw(frame)
self.backgroundColor = UIColor.gray
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
//Drawing of the white color in the image, over the blue background
override func draw(_ rect: CGRect) {
UIGraphicsBeginImageContextWithOptions(self.bounds.size, false, 0)
let context = UIGraphicsGetCurrentContext()
context?.setFillColor(UIColor.white.cgColor)
context?.setBlendMode(.normal)
context?.fill(self.bounds)
self.image = UIGraphicsGetImageFromCurrentImageContext()
self.alpha = 1
UIGraphicsEndImageContext()
}
//The method called from touchesMoved() to delete the white color
func eraseColumn() {
UIGraphicsBeginImageContextWithOptions(self.bounds.size, false, 0)
let context = UIGraphicsGetCurrentContext()
self.image?.draw(in: self.bounds)
context?.beginPath()
context?.addEllipse(in: CGRect(x: (lastPoint?.x)!, y: (lastPoint?.y)!, width: 10, height: 10))
context?.setLineCap(.round)
context?.setLineWidth(10)
context?.setStrokeColor(UIColor.clear.cgColor)
context?.setBlendMode(.clear)
context?.strokePath()
context?.closePath()
self.image = UIGraphicsGetImageFromCurrentImageContext()!
UIGraphicsEndImageContext()
}
//Touches handling
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
let touch = touches.first
firstPoint = touch?.location(in: self)
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
let touch = touches.first
lastPoint = touch?.location(in: self)
eraseColumn()
}
}
As you can see in the draw(_ rect: CGRect) method, I fill the image with white color and set it's background color to gray.
And in the eraseColumn() method, I delete the white color that the user touched. No matter what I try, the image is being deleted. I simply don't know why this is happening.
Any help would be very appreciated.
Project is in swift 3, X-Code 9.2.

Answer 1

Finally found the solution
changing
self.image?.draw(in: self.bounds)
to
self.image?.draw(at: self.bounds.origin)
fixes the problem. Hope it will help somebody.
Cheers