Turtle Graphics and Lindenmayer Systems Experiments

For information on L-Systems see Lindenmayer Systems, Fractals, and Plants or The Algorithmic Beauty of Plants

Key Classes, Structs and Protocols

• Turtle - A class that holds a location, direction and a renderer object

• TurtleAction - A struct that wraps a closure of the form (_ : Turtle) -> Void. Actions are simple instructions like move or turn and complex sequences of other actions.

• TurtleRenderer - A protocol for renderers. There are two implementations. One is an extentsion to CGContext. The other is a bounding box finder.

• TurtleView - A NS/UIView that holds a TurtleAction object and draws it scaled to the views bounds.

let flowsnake : TurtleAction = {
    let F = TurtleAction.move(by: 4)

    let x = [ "+" : TurtleAction.turn(by: +60),
              "-" : TurtleAction.turn(by: -60),
              "X" : F,
              "Y" : F ]

    let p = [ "X" : "X-Y--Y+X++XX+Y-",
              "Y" : "+X-YY--Y-X++X+Y" ]

    let a = "X"

    return .lindenmayer(axiom: a, rules: p, actions: x, depth: 4)
}()

let view = TurtleView(action: flowsnake)

let triangles = (1 ... 3).map({ (i : Int) -> TurtleAction in
    if (i % 2 == 1) {
        return .polygon(sideLength: 150, sideCount: 3, ccw: (i == 1), twist: 3, repeat: 50)
    } else {
        return .turn(by: 60)
    }
})

let view = TurtleView(action: .sequence(triangles, repeat: 6))

Requirements

Swift 4

Xcode 9 or Swift Playgrounds iPad app