円を描く

extension CGRect {
    init(_ center:CGPoint, _ size:CGSize) {
        self.origin = CGPoint(x:center.x - size.width/2, y:center.y - size.height/2)
        self.size = size
    }
}

extension CGPoint {
    init(_ x:CGFloat, _ y:CGFloat) {
        self.x = x
        self.y = y
    }
}

extension CGSize {
    init(_ width:CGFloat, _ height:CGFloat) {
        self.width = width
        self.height = height
    }
}

class RDView:UIView {
    
    func drawCircle(context:CGContext) {
        context.setLineWidth(20)
        context.strokeEllipse(in: CGRect(CGPoint(100,100), CGSize(100,100)))
        context.setFillColor(red: 1.0, green: 1.0, blue: 0.3, alpha: 0.3)
        context.setStrokeColor(red: 1.0, green: 0.3, blue: 0.5, alpha: 0.3)
        context.strokeEllipse(in: CGRect(x: 100, y: 100, width: 100, height: 100))
        context.fillEllipse(in: CGRect(x:120, y:120, width:60, height:60))
    }
    
    override func draw(_ rect: CGRect) {
        // Drawing code
        let p = UIGraphicsGetCurrentContext()
        drawCircle(context: p!)
    }
}

上のextensionは簡便のため。