如何更快地绘制UIView？

Question

我创建了一个半圆，根据我指定的值计算结束角度，这些值总是变化的。这一切都很完美，但问题是，当我测试应用程序时，我知道值已经更新但我需要大约40秒直到绘制半圆。如何让它看起来更快？

class Circle: UIView  {
    var muliplier: CGFloat = 1.0
    var centerOfCircleView: CGPoint {
        return CGPoint(x: bounds.midX, y: bounds.midY+40)
    }

    var halfOfViewsSize: CGFloat{
        return min(bounds.size.height, bounds.size.width) / 2 * muliplier
    }

    var lineWidth: CGFloat = 25
    // circles radius
    var half = CGFloat.pi
    var quarter = CGFloat(3 * CGFloat.pi / 2)

    var endAngle: CGFloat = 0.0 {
        didSet {
            setNeedsDisplay()
        }
    }

    override func draw(_ rect: CGRect) {
        super.draw(rect)
        self.drawCircleCenteredAtVariavel(center: centerOfCircleView, withRadius: halfOfViewsSize).stroke()
    }

    func drawCircleCenteredAtVariavel(center: CGPoint, withRadius radius: CGFloat) -> UIBezierPath {
        let  circlePath = UIBezierPath(arcCenter: centerOfCircleView, radius: halfOfViewsSize, startAngle: half, endAngle: endAngle , clockwise: true)         

        circlePath.lineWidth = lineWidth

        return circlePath
    }
}