'on motion notify event'

def _onmove(self, event):

    if (self.pressv is None):
        return
    (x, y) = self._get_data(event)
    if (x is None):
        return
    self.prev = (x, y)
    if (self.direction == u'horizontal'):
        v = x
    else:
        v = y
    (minv, maxv) = (v, self.pressv)
    if (minv > maxv):
        (minv, maxv) = (maxv, minv)
    if (self.direction == u'horizontal'):
        self.rect.set_x(minv)
        self.rect.set_width((maxv - minv))
    else:
        self.rect.set_y(minv)
        self.rect.set_height((maxv - minv))
    if (self.onmove_callback is not None):
        vmin = self.pressv
        (xdata, ydata) = self._get_data(event)
        if (self.direction == u'horizontal'):
            vmax = (xdata or self.prev[0])
        else:
            vmax = (ydata or self.prev[1])
        if (vmin > vmax):
            (vmin, vmax) = (vmax, vmin)
        self.onmove_callback(vmin, vmax)
    self.update()
    return False
