conic gradient

MVMCoreUI/Atomic/Atoms/Views/Wheel.swift

@@ -19,8 +19,6 @@ import UIKit
 // MARK: setup
     open override func setupView() {
         super.setupView()
-        //avoid adding height constraint multiple times
-        guard heightConstraint == nil else { return }
         heightConstraint = heightAnchor.constraint(equalToConstant: 0)
         heightConstraint?.isActive = true
         widthAnchor.constraint(equalTo: heightAnchor).isActive = true
@@ -51,6 +49,31 @@ import UIKit
         }
         heightConstraint?.constant = graphObject.diameter
         
+        // iOS 12 uses the conic gradient and a mask for simplicity.
+        if #available(iOS 12, *) {
+            let gradient = CAGradientLayer()
+            gradient.type = .conic
+            gradient.startPoint = CGPoint(x: 0.5, y: 0.5)
+            gradient.endPoint = CGPoint(x: 0.5, y: 0.0)
+            gradient.frame = CGRect(x: 0, y: 0, width: graphObject.diameter, height: graphObject.diameter)
+            gradient.colors = graphObject.colors.map({ (color) -> CGColor in
+                return color.cgColor
+            })
+            gradientLayer = gradient
+            layer.addSublayer(gradient)
+            
+            let center = CGPoint(x: gradient.bounds.midX, y: gradient.bounds.midY)
+            let radius = (graphObject.diameter - graphObject.lineWidth) / 2.0
+            let path = UIBezierPath(arcCenter: center, radius: radius, startAngle: (3 / 2 * .pi), endAngle: -(1 / 2 * .pi), clockwise: false)
+            let mask = CAShapeLayer()
+            mask.fillColor = UIColor.clear.cgColor
+            mask.strokeColor = UIColor.white.cgColor
+            mask.lineWidth = graphObject.lineWidth
+            mask.path = path.cgPath
+            gradient.mask = mask
+            return
+        }
+        
         //create circle path
         let radius = graphObject.diameter / 2.0