Mandelbrot F#

open System
open System.Drawing
open System.Drawing.Imaging
open System.Runtime.InteropServices

let CalcZ (coord:float * float) =

    let maxIterations = 255

    let rec CalcZHelper (xCoord:float) (yCoord:float) // line break inserted
           (x:float) (y:float) iters =
        let newx = x * x + xCoord - y * y
        let newy = 2.0 * x * y + yCoord
        match newx, newy, iters with
        | _ when Math.Abs newx > 2.0 -> iters
        | _ when Math.Abs newy > 2.0 -> iters
        | _ when iters = maxIterations -> iters
        | _ -> CalcZHelper xCoord yCoord newx newy (iters + 1)

    CalcZHelper (fst coord) (snd coord) (fst coord) (snd coord) 0

let colorArray = Array.init 256 (fun i -> [|byte i;byte i;byte i;255uy|])
let xDim = 1920
let yDim = 1200
let scale = 1./500.
let conv (x,y) =
    (float (x - xDim / 2 - (xDim / 4))) * scale
    ,(float (y - yDim / 2)) * scale
// Append this code with one of the following...


// Fast version:
let screen =
    Array.init (xDim*yDim) (fun i -> CalcZ <| conv (i % xDim, i / xDim))
    |> Array.collect (fun i -> colorArray.[i])
let gch = GCHandle.Alloc(screen, GCHandleType.Pinned)
let bmp = new Bitmap(xDim, yDim, xDim * 4, PixelFormat.Format32bppArgb, gch.AddrOfPinnedObject())
gch.Free()
bmp.Save(@"C:\Documents and Settings\All Users\Desktop\out.png")


// Low memory version:
let screen =
    Seq.init (xDim*yDim) (fun i -> CalcZ <| conv (i % xDim, i / xDim))
    |> Seq.collect (fun i -> colorArray.[i])
    |> Seq.toArray
let gch = GCHandle.Alloc(screen, GCHandleType.Pinned)
let bmp = new Bitmap(xDim, yDim, xDim * 4, PixelFormat.Format32bppArgb, gch.AddrOfPinnedObject())
gch.Free()
bmp.Save(@"C:\Documents and Settings\All Users\Desktop\out.png")