anchor.diff:      let keyboard = new Aardvark.Application.WinForms.Keyboard()
       let mouse = new Aardvark.Application.WinForms.Mouse()
       let sizes = Mod.init (V2i(base.ActualWidth, base.ActualHeight))
  +
  +    let actualSize = 
  +        adaptive {
  +            let! s = sizes
  +            match impl with
  +             | Some v -> 
  +                printfn "switched to impl"
  +                return! v.Sizes
  +             | None -> return s
  +        }
  +
       let mutable inner : Option<IMod<DateTime>> = None
       let time = 
           Mod.custom (fun () -> 
  
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:                 | 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 -> ()
  