Spirograph playground based on Erica Sadun's

gistfile1.swift

import UIKit
import Foundation
import XCPlayground


struct SpirographGenerator : GeneratorType {
    
    var pointOffset, dTheta, dR, minorRadius, majorRadius : Double
    var theta = 0.0
    typealias Element = CGPoint
    
    init(majorRadius : Double, minorRadius : Double, pointOffset : Double, samples : Double)
    {
        self.pointOffset = pointOffset
        self.dTheta = Double(M_PI) * (2.0) / samples
        self.majorRadius = majorRadius
        self.minorRadius = minorRadius
        self.dR = majorRadius - minorRadius
    }
    
    mutating func next() -> CGPoint? {
        var xT : Double = dR * cos(theta) + pointOffset * cos(dR * theta / minorRadius)
        var yT : Double = dR * sin(theta) + pointOffset * sin (dR * theta / minorRadius)
        theta = theta + dTheta
        return CGPoint(x: xT, y: yT)
    }
}

class SpiroView : UIView {
    var gen:SpirographGenerator = SpirographGenerator(majorRadius: 100, minorRadius: 12, pointOffset: 22, samples: 500)
    var points:Int = 50 {
        didSet {
            setNeedsDisplay()
        }
    }
    var strokeColor:UIColor = UIColor.whiteColor()
    
    override func drawRect(rect: CGRect) {
        let midX = rect.width / 2
        let midY = rect.height / 2
        let ctx = UIGraphicsGetCurrentContext()
        strokeColor.set()
        for x in 1..<points {

            if let p = gen.next() {
                CGContextAddEllipseInRect(ctx, CGRect(x: p.x + midX, y: p.y + midY, width: 1, height: 1))
            }
        }
        CGContextDrawPath(ctx, kCGPathFillStroke)
    }
}

let v = SpiroView(frame: CGRect(x:0, y:0, width:250, height:250))
v.strokeColor = UIColor.redColor()
v.points = 8000