Fractal tree in F#. Our solution from dojo in Copenhagen, 2017-05-30

FractalTree.fsx

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

// Create a form to display the graphics
let width, height = 500, 500         
let form = new Form(Width = width, Height = height)
let box = new PictureBox(BackColor = Color.White, Dock = DockStyle.Fill)
let image = new Bitmap(width, height)
let graphics = Graphics.FromImage(image)
//The following line produces higher quality images, 
//at the expense of speed. Uncomment it if you want
//more beautiful images, even if it's slower.
//Thanks to https://twitter.com/AlexKozhemiakin for the tip!
graphics.SmoothingMode <- System.Drawing.Drawing2D.SmoothingMode.HighQuality
let brush = new SolidBrush(Color.FromArgb(0, 0, 0))

box.Image <- image
form.Controls.Add(box) 

// Compute the endpoint of a line
// starting at x, y, going at a certain angle
// for a certain length. 
let endpoint x y angle length =
    x + length * cos angle,
    y + length * sin angle

let flip x = (float)height - x

// Utility function: draw a line of given width, 
// starting from x, y
// going at a certain angle, for a certain length.
let drawLine (target : Graphics) (brush : Brush) 
             (x : float) (y : float) 
             (angle : float) (length : float) (width : float) =
    let x_end, y_end = endpoint x y angle length
    let origin = PointF((single)x, (single)(y |> flip))
    let destination = PointF((single)x_end, (single)(y_end |> flip))
    let pen = new Pen(brush, (single)width)
    target.DrawLine(pen, origin, destination)

let draw = drawLine graphics brush

let pi = Math.PI

type Line = { X : float; Y : float; Angle : float; Length : float; Width : float }

let drawL line = draw line.X line.Y line.Angle line.Length line.Width

type Parameters = { LeftAngle : float; RightAngle : float; ShrinkFactor : float }

let getBranches p line =
    let x, y = endpoint line.X line.Y line.Angle line.Length
    let left = {
        X = x
        Y = y
        Angle = (pi * (line.Angle / pi + p.LeftAngle))
        Length = line.Length * p.ShrinkFactor
        Width = line.Width * p.ShrinkFactor }
    let right = {
        X = x
        Y = y
        Angle = (pi * (line.Angle / pi - p.RightAngle))
        Length = line.Length * p.ShrinkFactor
        Width = line.Width * p.ShrinkFactor }
    [left; right]

let rec createTree counter p trunk =
    if counter > 0
    then        
        let branches = getBranches p trunk
        trunk :: List.collect (createTree (counter - 1) p) branches
    else [trunk]

{ X = 250.; Y = 50.; Angle = (pi*(0.5)); Length = 100.; Width = 4. }
|> createTree 10 { LeftAngle = 0.1; RightAngle = 0.1; ShrinkFactor = 0.8 }
|> List.iter drawL

form.ShowDialog()