anchor.diff:                  | None -> DateTime.Now
              )
   
  -    let setControl (self : RenderControl) (c : FrameworkElement) (cr : IRenderTarget) =
  +    member x.SetControl (self : RenderControl) (c : FrameworkElement) (cr : IRenderTarget) =
           match impl with
               | Some i -> failwith "implementation can only be set once per control"
               | None -> ()
  
positive.code: 
      member x.Implementation
          with get() = match ctrl with | Some c -> c | _ -> null
          and set v = setControl x v (v |> unbox<IRenderTarget>)
  
      member x.Runtime = runtime
      member x.Sizes = sizes :> IMod<V2i>
      member x.Samples = impl.Value.Samples
  
      member x.Keyboard = keyboard :> IKeyboard
  
negative.code:             | Some task -> cr.RenderTask <- task
              | None -> ()
  
  
          ctrl <- Some c
          impl <- Some cr
          transact(fun () ->
              cr.Time.AddOutput(time)
              inner <- Some cr.Time
  
              Mod.change sizes V2i.OO
          )
  
      override x.OnRenderSizeChanged(e) =
          base.OnRenderSizeChanged(e)
  