All views have a
mask property that allows you to cut out parts depending on what you need. This mask can be any other kind of
UIView, so you could for example use a label to cut out an image view.
To try it out, first create a view with some obvious content such as a background color:
let redView = UIView(frame: CGRect(x: 50, y: 50, width: 128, height: 128)) redView.backgroundColor = .red view.addSubview(redView)
Now create your mask as a separate
UIView. Although it won’t be directly visible you should give this either a background color or some other content because the alpha channel of this mask determines what shows through in the original view.
To demonstrate this, here’s a mask view that’s the same size as the original view, but it’s offset 64 pixels to the right and has a 64-point corner radius. When used as a mask for the previous view it will have the effect of turning it into a semi-circle:
let maskView = UIView(frame: CGRect(x: 64, y: 0, width: 128, height: 128)) maskView.backgroundColor = .blue maskView.layer.cornerRadius = 64 redView.mask = maskView
The blue background color won’t be visible – that’s just there to make sure all pixels in the mask are opaque.
Available from iOS 8.0
Did this solution work for you? Please pass it on!
Other people are reading…
About the Swift Knowledge Base
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
Upgrade to premium
The Hacking with Swift guide book helps you learn faster, plus get an Xcode tips and tricks video and Swift wall chart.