How to intersect two rects in iOS?

Question

I would like to remove the "blue" circle and just have a "hollow" center (so there's only the red layer and you can see the background inside). Filling the inside with the clear color doesn't work.

class AddButtonView: UIView {

    override func draw(_ rect: CGRect) {
        super.draw(rect)
        // Outer circle
        UIColor.red.setFill()
        let outerPath = UIBezierPath(ovalIn: rect)
        outerPath.fill()

        // Center circle
        UIColor.blue.setFill()
        let centerRect = rect.insetBy(dx: rect.width * 0.55 / 2, dy: rect.height * 0.55 / 2)
        let centerPath = UIBezierPath(ovalIn: centerRect)
        centerPath.fill()
    }
}

How can I do it? intersects didn't do anything.

André Slotta · Accepted Answer · 2018-12-15T13:44:34.330

1

override func draw(_ rect: CGRect) {
    super.draw(rect)

    // Outer circle
    UIColor.red.setFill()
    let outerPath = UIBezierPath(ovalIn: rect)
    outerPath.fill()

    guard let context = UIGraphicsGetCurrentContext() else { return }

    context.saveGState()
    context.setBlendMode(.destinationOut)

    // Center circle
    UIColor.blue.setFill()
    let centerRect = rect.insetBy(dx: rect.width * 0.55 / 2, dy: rect.height * 0.55 / 2)
    let centerPath = UIBezierPath(ovalIn: centerRect)
    centerPath.fill()

    context.restoreGState()
}

Do not forget to give the view a backgroundColor of .clear and set its isOpaque property to false.

Inspired by Draw transparent UIBezierPath line inside drawRect.

Result:

edited Dec 15 '18 at 13:44

answered Dec 15 '18 at 12:37

André Slotta

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I'm sorry, this only adds a black background to the view. It does not solve my question. – Cesare Dec 15 '18 at 13:37
Updated my answer with the result. Did you set the view's `backgroundColor` to `.clear`? And `isOpaque` to false? – André Slotta Dec 15 '18 at 13:38
Thanks, settings `isOpaque` to false did the trick! You may want to update your answer with that info. – Cesare Dec 15 '18 at 13:43

How to intersect two rects in iOS?

1 Answers1