def start_pan(self, x, y, button):
        bd = self.viewer.get_bindings()
        data_x, data_y = self.viewer.get_data_xy(x, y)
        bd.ms_pan(self.viewer, 'down', data_x, data_y)
Called when a pan operation has started.
dataset/ETHPy150Open ejeschke/ginga/ginga/mplw/transform.py/GingaAxes.start_pan