def _containsEvent( self, event ):
        """
        Checks that the event occured in the L{RoundButton} circle.

        :param `event`: a `wx.MouseEvent` event.
        """
        x, y, width, height = self.GetClientRect()
        x += width // 2
        y += height // 2
        px, py = event.GetPosition().Get()
        dx = px - x
        dy = py - y
        return dx * dx + dy * dy < self._buttonRadius * self._buttonRadius

        Checks that the event occured in the L{RoundButton} circle.

        :param `event`: a `wx.MouseEvent` event.
        
recipes/Python/577951_wxPythDramatic_shaded_3D_buttons_that_look_like_/recipe-577951.py