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