class my_main_window : public Withmy_main_windowLayout<TopWindow> {

	[...misc stuff...]

	//Event<> WhenLayout; // not even necessary
	void Layout() override
	{
		// first and foremost, do whatever you need to 
		// with all the widgets (resize etc)
		Withmy_main_windowLayout<TopWindow>::Layout();

		// and then finally, mess with the ScatterCtrl
		set_chart_grid();

		Chart1.Refresh();  // doesn't make a difference
		Ctrl::ProcessEvents(); // doesn't make a difference
		//PromptOK("hello there");  // DOES make a difference?
	}
}