anchor.diff:      Div [ Width (string width); Attr.Style "float:left" ] -< [
         Div [ Attr.Style "float:center" ] -< [
           element
  +        |>! OnMouseMove (movePlayerShip element playerShip)
         ]
       ]
   
  
positive.code:     let rec loop =
        async {
          do drawBackground ctx
          do! Async.Sleep (1000 / fps)
          do! loop
        }
  
negative.code:     ctx.Fill()
  
    [<JavaScript>]
    let drawPlayerShip (ctx : CanvasRenderingContext2D) playerShip =
      ctx.Save()
      ctx.BeginPath()
      ctx.Translate(playerShip.x, playerShip.y)
      ctx.MoveTo(0., -10.)
      ctx.LineTo(-10., 10.)
      ctx.LineTo(10., 10.)
      ctx.FillStyle <- "rgb(64, 64, 255)"
      ctx.Fill()
      ctx.Restore()
  
    [<JavaScript>]
    let movePlayerShip (element : Element) playerShip _ (point : Events.MouseEvent) =
      let offset = JQuery.JQuery.Of(element.Dom).Offset()
      let x = float (point.X - offset.Left)
      let y = float (point.Y - offset.Top)
      playerShip := { x = x; y = y }
  
    [<JavaScript>]
    let animatedCanvas width height =
  
      let playerShip = ref { x = 0.; y = 0. }
  
      // キャンバスの設定
      let element = Tags.NewTag "Canvas" []
  