def create_ui(self):
        '''
        .. versionchanged:: 0.20
            Debounce window expose and resize handlers to improve
            responsiveness.

        .. versionchanged:: X.X.X
            Call debounced `_on_expose_event` handler on _leading_ edge to make
            UI update more responsive when, e.g., changing window focus.

            Decrease debounce time to 250 ms.
        '''
        super(GtkShapesCanvasView, self).create_ui()
        self.widget.set_events(gtk.gdk.BUTTON_PRESS |
                               gtk.gdk.BUTTON_RELEASE |
                               gtk.gdk.BUTTON_MOTION_MASK |
                               gtk.gdk.BUTTON_PRESS_MASK |
                               gtk.gdk.BUTTON_RELEASE_MASK |
                               gtk.gdk.POINTER_MOTION_HINT_MASK)
        self._dirty_check_timeout_id = gtk.timeout_add(30, self.check_dirty)

        self.resize = Debounce(self._resize, wait=250)
        debounced_on_expose_event = Debounce(self._on_expose_event, wait=250,
                                             leading=True, trailing=True)
        self.widget.connect('expose-event', debounced_on_expose_event)