Loewensberg Lines

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

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

let width, height = 512, 512

let blue = (2, 89, 148)
let yellow = (252, 173, 6)
let red = (200, 1, 44)
let purple = (116, 56, 119)

let pattern w h = [
   (-1, 0), (0,0);
   ( 0, 1), (0,h-1);
   ( 1, 0), (w-1,h-1);
   ( 0,-1), (w-1,4)
   (-1, 0), (4,4)
   ]

let path w h =
   let x, y = ref (w-1), ref 0
   [for (dx,dy), (x1,y1) in pattern w h do
      while !x <> x1 || !y <> y1 do
         yield !x,!y
         x := !x + dx
         y := !y + dy
   ]

let draw () =
   let image = new Bitmap(width, height)
   use graphics = Graphics.FromImage(image)
   let color = Color.FromArgb(255,234,236,232)
   let brush = new SolidBrush(color)
   graphics.FillRectangle(brush, 0, 0, width, height)

   let colors = [blue; yellow; red; purple]
   for i = 0 to 3 do
      let w,h = 25-i*2, 25 - i*2
      let points = path w h
      let n = points.Length
      for (x,y) in points |> Seq.take (n-(i+2)*1) |> Seq.skip ((3-i)*3) do
         let r,g,b = colors.[i]
         let color = Color.FromArgb(255,r,g,b)
         let brush = new SolidBrush(color)
         graphics.FillRectangle(brush, (1+x+i)*19, (1+y+i)*19, 19, 19)
   image

let show () =
   let image = draw ()
   let form = new Form (Text="Loewensberg Lines", Width=320+16, Height=320+36)
   let picture = new PictureBox(Dock=DockStyle.Fill, Image=image)
   image.Save(@"C:\temp\Loewensberg Lines.png", Imaging.ImageFormat.Png)
   do  form.Controls.Add(picture)
   form.ShowDialog() |> ignore

show()