'GtkDrawable draw event, like expose_event in GTK 2.X'

def on_draw_event(self, widget, ctx):

    self._renderer.set_context(ctx)
    allocation = self.get_allocation()
    (x, y, w, h) = (allocation.x, allocation.y, allocation.width, allocation.height)
    self._render_figure(w, h)
    return False
