SwiftCubicSpline

let spline = CubicSpline(points: [
    Point(x: 0.0, y: 0.5),
    Point(x: 0.1, y: 0.5),
    Point(x: 0.2, y: 0.7),
    Point(x: 0.4, y: 0.3),
    Point(x: 0.6, y: 0.6),
    Point(x: 0.8, y: 0.4),
    Point(x: 0.9, y: 0.5),
    Point(x: 1.0, y: 0.5)
    ])

let graphSize = self.bounds.size
for y in 0 ..< Int(graphSize.height) {
    let y = Double(y)
    let x = spline[x: y/Double(graphSize.height)] * Double(graphSize.width)

    if y == 0 {
        context.move(to: CGPoint(x: x, y: y))
    } else {
        context.addLine(to: CGPoint(x: x, y: y))
    }
}
context.strokePath()