# File easy_vtk.rb, line 1024
  def gui_start
    iren = Vtk::RenderWindowInteractor.new
    iren.SetRenderWindow( @renWin )
    iren.Initialize
    if block_given?
      proc = Proc.new{|widget, event|
        if widget.GetKeySym == 'Return'
          yield
          @renWin.Render
        end
      }
      iren.AddObserver('KeyPressEvent', proc )
    end
    iren.Start
    return nil
  end