Create CAGradient Layer with transparent hole in it? - ios

Question

Currently I do it like this:
final class BorderedButton: BottomNavigationButton {
private let gradient = CAGradientLayer()
private let shapeLayer = CAShapeLayer()
override func layoutSubviews() {
super.layoutSubviews()
let radius = bounds.size.height / 2
let outside = UIBezierPath(roundedRect: CGRect(x: 0.0, y: 0.0, width: bounds.width, height: bounds.height), cornerRadius: radius)
let inside = UIBezierPath(roundedRect: CGRect(x: 3.0, y: 3.0, width: bounds.width - 6, height: bounds.height - 6), cornerRadius: radius - 3)
outside.append(inside)
outside.usesEvenOddFillRule = true
shapeLayer.path = outside.cgPath
}
init(color: UIColor?) {
super.init(frame: .zero)
let isGradient = color == nil
shapeLayer.fillRule = kCAFillRuleEvenOdd
shapeLayer.fillColor = UIColor.red.cgColor
layer.insertSublayer(shapeLayer, at: 0)
//gradient part
gradient.colors = isGradient ? [Constants.gradientStart, Constants.gradientEnd] : [color!.cgColor, color!.cgColor]
gradient.startPoint = CGPoint(x: 0.2, y: 0.5)
gradient.endPoint = CGPoint(x: 1, y: 1)
}
}
How can I apply that gradient to my code?

Answer 1

Don't add the CAShapeLayer to the view's layer, rather set it as the mask of the CAGradientLayer. Also don't forget to set the bounds of the gradient layer.
I had to make some modifications to get it to run in a playground, but this works for me:
let gradientStart = UIColor.orange
let gradientEnd = UIColor.blue
final class BorderedButton: UIButton {
private let gradient = CAGradientLayer()
private let shapeLayer = CAShapeLayer()
override func layoutSubviews() {
super.layoutSubviews()
let radius = bounds.size.height / 2
let outside = UIBezierPath(roundedRect: CGRect(x: 0.0, y: 0.0, width: bounds.width, height: bounds.height), cornerRadius: radius)
let inside = UIBezierPath(roundedRect: CGRect(x: 3.0, y: 3.0, width: bounds.width - 6, height: bounds.height - 6), cornerRadius: radius - 3)
outside.append(inside)
outside.usesEvenOddFillRule = true
shapeLayer.path = outside.cgPath
gradient.frame = CGRect(x: 0, y: 0, width: bounds.size.width, height: bounds.size.height)
}
init(color: UIColor?, frame: CGRect = .zero) {
super.init(frame: frame)
let isGradient = color == nil
shapeLayer.fillRule = kCAFillRuleEvenOdd
//gradient part
gradient.colors = isGradient ? [gradientStart.cgColor, gradientEnd.cgColor] : [color!.cgColor, color!.cgColor]
gradient.startPoint = CGPoint(x: 0.2, y: 0.5)
gradient.endPoint = CGPoint(x: 1, y: 1)
gradient.mask = shapeLayer
layer.addSublayer(gradient)
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}