Foo Satellite Animation

open System.Windows.Forms
open System.Drawing

type Direction =
    |Up
    |Down
    |Right
    |Left

type Animation() as this =

    inherit Control()

    let mutable posX, posY = this.Width/2 - 50, this.Height/2 - 50 // pos del satellite
    let mutable dir = Down

    let timer = new Timer(Interval = 30)

    // mi serve per capire se p è all'interno di r
    let correlate (p:Point) (r:Rectangle) =
        let mutable res = true
        if p.X <= r.X || p.X >= r.X + r.Width || p.Y <= r.Y || p.Y >= r.Y + this.Height then
            false
        else
            true

    //do this.SetStyle(ControlStyles.OptimizedDoubleBuffer,true) in questo caso non serve -> niente flicker comunque
    do timer.Tick.Add(fun e ->
       match dir with
       | Down -> posY <- posY + 5
                 if posY >= this.Height/2 + 50 then dir <- Right
       | Right -> posX <- posX + 5
                  if posX >= this.Width/2 + 50 then dir <- Up
       | Up -> posY <- posY - 5
               if posY <= this.Height/2 - 50 then dir <- Left
       | Left -> posX <- posX - 5
                 if posX <= this.Width/2 - 50 then dir <- Down
       this.Invalidate()
       )

    override this.OnPaint e =
        let g = e.Graphics
        g.FillEllipse(Brushes.Yellow, this.Width/2 - 25, this.Height/2 - 25, 50, 50) // pivot
        g.FillEllipse(Brushes.Black, posX, posY, 10, 10) // satellite
        g.FillRectangle(Brushes.Green, 5, 5, 50, 20) // bottone play
        g.FillRectangle(Brushes.Red, 5, 30, 50, 20) // bottone stop

    override this.OnResize e =
        // ripristino
        posX <- this.Width/2 - 50
        posY <- this.Height/2 - 50
        dir <- Down
        this.Invalidate()

    override this.OnMouseDown e =
        let rplay = new Rectangle(5, 5, 50, 20)
        let rstop = new Rectangle(5, 30, 50, 20)
        if correlate e.Location rplay then
            timer.Start() // ha cliccato su play
        if correlate e.Location rstop then
            timer.Stop() // ... su stop
        this.Invalidate()

     override this.OnKeyDown e =
         match e.KeyCode with
         | Keys.P -> timer.Start() //play
                     this.Invalidate()
         | Keys.X -> timer.Stop() //stop
                     this.Invalidate()
         | _ -> ()

// testing
let f = new Form(Text="Animation", TopMost=true)
f.Show()
let a = new Animation(Dock=DockStyle.Fill)
f.Controls.Add(a)