punch a clear hole in a UIImage - swift

Question

I'm trying to have a transperant hole in a uiimage This is what I found so far:
let hole = CGRect(x: 0, y: 0, width: 50, height: 50)
let context = UIGraphicsGetCurrentContext()!
context.clear(hole)
myImage.image = UIGraphicsGetImageFromCurrentImageContext()!
UIGraphicsEndImageContext()
but I get nil at : let context = UIGraphicsGetCurrentContext()!
I understand that I need to define current context somewhere but I'm not sure where and how

Answer 1

You need to have a context available to draw with. Create one explicitly with UIGraphicsBeginImageContext, and when you are done drawing, call UIGraphicsEndImageContext to clean it up.
Here your code, with the call to UIGraphicsBeginImageContext, wrapped in an extension method:
extension UIImage {
func imageWithHole(at rect: CGRect) -> UIImage? {
UIGraphicsBeginImageContext(self.size)
guard let context = UIGraphicsGetCurrentContext() else { return nil }
self.draw(at: CGPoint.zero)
context.clear(rect)
let resultImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return resultImage
}
}
Use it like this:
let sourceImage = UIImage(named: "sample.jpg")
let imageWithHole = sourceImage?.imageWithHole(at: CGRect(x: 50, y: 50, width: 50, height: 50))