Koch Snowflake

#r "System.Drawing.dll"
#r "System.Windows.Forms.dll"

open System
open System.Drawing
open System.Windows.Forms

let width, height = 512, 512

let black = 0,0,0
let white = 255,255,255
let red = 183,51,32
let green = 45, 140, 108
let blue = 68, 116, 178

let toBrush (r,g,b) =
   let color = Color.FromArgb(255,r,g,b)
   new SolidBrush(color)

let snowflake (graphics:Graphics) length =
   let pen = ref (new Pen(toBrush white))
   let angle = ref 0
   let x = ref ((float width/2.0) - length/2.0)
   let y = ref ((float height/2.0) - length/3.0)
   let n = length

   let rec draw n depth =
      if depth = 0 then
         line n
      else
         let d = n/3.0
         pen := new Pen(toBrush red)
         draw (n/3.0) (depth-1)
         rotate -60
         pen := new Pen(toBrush green)
         draw (n/3.0) (depth-1)
         rotate 120
         pen := new Pen(toBrush blue)
         draw (n/3.0) (depth-1)
         rotate -60
         pen := new Pen(toBrush red)
         draw (n/3.0) (depth-1)
   and line n =
      let r = (float !angle * Math.PI) / 180.0
      let x2 = float !x + cos(r) * n
      let y2 = float !y + sin(r) * n
      graphics.DrawLine(!pen, float32 !x,float32 !y, float32 x2, float32 y2)
      x := x2
      y := y2
   and rotate a =
      angle := !angle + a

   let depth = 3
   pen := new Pen(toBrush red)
   draw n depth
   rotate 120
   pen := new Pen(toBrush green)
   draw n depth
   pen := new Pen(toBrush blue)
   rotate 120
   draw n depth

let draw () =
   let image = new Bitmap(width, height)
   use graphics = Graphics.FromImage(image)
   let brush = toBrush black
   graphics.FillRectangle(brush, 0, 0, width, height)
   for i in 10.0..20.0..360.0 do
      snowflake (graphics) i
   image

let show () =
   let image = draw ()
   let form = new Form (Text="Koch Snowflake", Width=width+16, Height=height+36)
   let picture = new PictureBox(Dock=DockStyle.Fill, Image=image)
   image.Save(@"C:\app\Koch.png", Imaging.ImageFormat.Png)
   do  form.Controls.Add(picture)
   form.ShowDialog() |> ignore

show()