Undoing a path drawn on UIImageView in Swift - swift

Question

I made an erase-effect on UIImageView by drawing a path with blend mode set to clear using the code below. How can I undo a given path, meaning restoring the original image under that path?
func erase(from fromPoint: CGPoint, to toPoint: CGPoint) {
UIGraphicsBeginImageContext(self.frame.size)
image?.draw(in: self.bounds)
defer {
self.image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
}
let path = CGMutablePath()
path.move(to: fromPoint)
path.addLine(to: toPoint)
let context = UIGraphicsGetCurrentContext()!
context.setShouldAntialias(true)
context.setLineCap(.round)
context.setLineWidth(40)
context.setBlendMode(.clear)
context.addPath(path)
context.strokePath()
}

Answer 1

The issue is that you creating a new UIImage, discarding what was there.
Two options:
Save a copy of your old image and restore it when you want to revert.
Alternatively, don’t alter the image at all, and instead just apply a mask to the UIImageView:
extension UIImageView {
func erase(from fromPoint: CGPoint, to toPoint: CGPoint) {
let maskImage = UIGraphicsImageRenderer(bounds: bounds).image { rendererContext in
let context = rendererContext.cgContext
context.fill(bounds)
let path = CGMutablePath()
path.move(to: fromPoint)
path.addLine(to: toPoint)
context.setShouldAntialias(true)
context.setLineCap(.round)
context.setLineWidth(40)
context.setBlendMode(.clear)
context.addPath(path)
context.strokePath()
}
mask = UIImageView(image: maskImage)
}
}
Then, when you want to reverse it, just remove the mask.