动画图像图形上下文Swift

Question

我目前有这个代码，它允许我使用Image Graphics Context创建一个呼吸描记器：

func generateSpirograph(insideRadius: Double = 0.5, rotationalSpeed: Double = -31/3, color: UIColor = .blue) {
    //Creates an 800*800 image that is transparent
    guard let transparentImage = UIImage(named: "transparent.png") else { return }
    let imgCenter = CGPoint(x: transparentImage.size.width/2, y: transparentImage.size.height/2)
    var multiplier: Double!

    if insideRadius <= 1 {
        multiplier = (2 - insideRadius)*100
    } else {
        multiplier = 150/insideRadius
    }

    //The size of the new bitmap
    UIGraphicsBeginImageContext(transparentImage.size)
    transparentImage.draw(at: .zero)

    //Setup Context
    guard let context = UIGraphicsGetCurrentContext() else { return }
    context.move(to: CGPoint(x: multiplier*(1+insideRadius)+Double(imgCenter.x), y: Double(imgCenter.y)))

    for t in 0 ... 2000 {
        let radians = Double(t) * Double.pi / 180
        let x = (cos(radians)+insideRadius*cos(rotationalSpeed*radians))
        let y = (sin(radians)+insideRadius*sin(rotationalSpeed*radians))
        //            let x = (outsideRadius+insideRadius)*sin(location*radians)+penLocation*insideRadius*sin(rotationalSpeed*location*radians)
        //            let y = (outsideRadius+insideRadius)*cos(location*radians)+penLocation*insideRadius*cos(rotationalSpeed*location*radians)

        context.addLine(to: CGPoint(x: multiplier*x+Double(imgCenter.x), y: multiplier*y+Double(imgCenter.y)))
    }

    context.setLineWidth(1)
    context.setStrokeColor(color.cgColor)
    context.drawPath(using: .stroke)

    guard let spirographImg = UIGraphicsGetImageFromCurrentImageContext() else { return }
    UIGraphicsEndImageContext()

    let spirographImageView = UIImageView(image: spirographImg)
    spirographImageView.contentMode = .scaleAspectFit

    spirographImageView.translatesAutoresizingMaskIntoConstraints = false
    spirographImageView.frame = CGRect(x: 0, y: 0, width: view.frame.width/2, height: view.frame.width/2)

    view.addSubview(spirographImageView)
}

它会立即运行，然后一次性绘制肺活量图。我想要发生的是它的动画，所以你可以看到正在形成的线。我怎么能这样做？

谢谢！