Animate drawing sine wave. CABasicAnimation and UIBezierPath

ViewController.swift

// Draw a sine curve with a fill

let centerY = frame.height / 2  // find the vertical center
let steps = 200                 // Divide the curve into steps
let stepX = frame.width / CGFloat(steps) // find the horizontal step distance

// Make a path
let path = UIBezierPath()
path.moveToPoint(CGPoint(x: 0, y: centerY))
// Loop and draw steps in straingt line segments
for i in 0...steps {
    let x = CGFloat(i) * stepX
    let y = (sin(Double(i) * 0.1) * 40) + Double(centerY)
    path.addLineToPoint(CGPoint(x: x, y: CGFloat(y)))
}

pathLayer.path = path.CGPath
pathLayer.lineWidth = 3
pathLayer.fillColor = UIColor.clearColor().CGColor
pathLayer.strokeColor = UIColor.redColor().CGColor
pathLayer.strokeStart = 0
pathLayer.strokeEnd = 0 // <<

let animation = CABasicAnimation(keyPath: "strokeEnd")
animation.fromValue = 0
animation.toValue = 1
animation.duration = 3
pathLayer.addAnimation(animation, forKey: "strokeEnd")