Using an UIView as a Mask in another UIView on Swift

Question

I am developing an App on xCode with Swift. My screen has an Image of an animal (outlet "backImage"), over this image I have a view (outlet "coverView"), color black, which covers all the screen. So so far you can't see the animal image, because the "coverView" is in front of it. Then I have another view (outlet "maskView") which is smaller and it's over the big view "coverView". What I want is to use this "maskView" as mask and therefor see the "backImage" through it, like a window.

Is there anyone out there able to figure this out?

Here is my screen, I want to see the woman character behind the big gray view through the smaller white view:

Solution

You can set the alpha property from your mask view and add in front of the other view, for instance:

let maskView = UIView()
maskView.backgroundColor = UIColor(white: 0, alpha: 0.5) //you can modify this to whatever you need
maskView.frame = CGRect(x: 0, y: 0, width: imageView.frame.width, height: imageView.frame.height)

yourView.addSubview(maskView)

---

EDIT: Now that you edited your question with an image, now I see what you need, so here is how you can accomplish that.

func setMask(with hole: CGRect, in view: UIView){

    // Create a mutable path and add a rectangle that will be h
    let mutablePath = CGMutablePath()
    mutablePath.addRect(view.bounds)
    mutablePath.addRect(hole)

    // Create a shape layer and cut out the intersection
    let mask = CAShapeLayer()
    mask.path = mutablePath
    mask.fillRule = kCAFillRuleEvenOdd

    // Add the mask to the view
    view.layer.mask = mask

}

With this function, all you need is to have a view and create a shape that it's going to be a hole in that view, for instance:

// Create the view (you can also use a view created in the storyboard)
let newView = UIView(frame: CGRect(x: 0, y: 0, width: view.frame.width, height: view.frame.height))
newView.backgroundColor = UIColor(white: 0, alpha: 1)

// You can play with these values and find one that fills your need
let rectangularHole = CGRect(x: view.bounds.width*0.3, y: view.bounds.height*0.3, width: view.bounds.width*0.5, height: view.bounds.height*0.5)

// Set the mask in the created view        
setMask(with: rectangularHole, in: newView)

Comments

[DevRenanGaspar]

Hi Alexandre, not sure if I am doing it correctly, but didn't work. If I understood correctly your code, you are creating a UIView with background white 0 and alpha 0.5, then define the size and add under my big View.. The problem what I want to see is behind the big view, so this new UIView has to make a hole in my big view. Thanks for your help!

[DevRenanGaspar]

I have now attached my screen

[Alexandre Lara]

@DevRenanGaspar Now that I saw the image I think that I know what you need so I edited my answer.

[DevRenanGaspar]

You are the best! Thank you so much. It works really well! Just a little change, instead of creating the rectangularHole by coding as you did, can use a view from my storyboard as the rectangularHole? I know I can replace the newView you created by one in my SB, I understood that and I actually did it. But can I do the same for the hole? Thanks again!

[DevRenanGaspar]

I think I got it! Can't believe, too many hours with this issue... I replaced the rectangularHole creation with CGRect by "let rectangularHole = windowView.frame.integral"... Please let me know if you would do different, but it worked! Thank you!

[Alexandre Lara]

@DevRenanGaspar You're welcome. It has been a while since I don't use storyboards so I really don't know if I would use a different way, but if yours is working, that's perfect. Happy coding!

[Narasimha Nallamsetty]

Hi @DevRenanGaspar, I have same requirement in my project. I have used the above code which you posted. It is not serving my purpose. Please help me with some example app or with more explanation. Thank you