anchor.diff:      let mutable lookat = rot * Matrix4.LookAt(eye, Vector3.Zero, Vector3.UnitY)
       GL.UniformMatrix4(modelViewLocation, false, &lookat)
   
  +    refresh_drawables ()
       for drawable in drawables do
         drawable.render vertexLocation
   
  
positive.code:     base.OnRenderFrame e
  
  module Library =
    let game = new Game()
    let version = GL.GetString(StringName.Version)
    let N = 10
    printfn "GL version: %A" version
    printfn "Generating %d random markers" N
    Simulator.generate N
    do game.Run(30.)
  
negative.code:     if base.Keyboard.[Key.Escape] then base.Close()
      if base.Keyboard.[Key.Right] then
        Simulator.advance ()
  
    override o.OnRenderFrame(e) =
      GL.Clear(ClearBufferMask.ColorBufferBit ||| ClearBufferMask.DepthBufferBit)
  