def __init__(self, ax, onselect, direction, minspan=None, useblit=False, rectprops=None, onmove_callback=None):
        """
        Create a span selector in ax.  When a selection is made, clear
        the span and call onselect with

          onselect(vmin, vmax)

        and clear the span.

        direction must be 'horizontal' or 'vertical'

        If minspan is not None, ignore events smaller than minspan

        The span rect is drawn with rectprops; default
          rectprops = dict(facecolor='red', alpha=0.5)

        set the visible attribute to False if you want to turn off
        the functionality of the span selector


        """
        if rectprops is None:
            rectprops = dict(facecolor='red', alpha=0.5)

        assert direction in ['horizontal', 'vertical'], 'Must choose horizontal or vertical for direction'
        self.direction = direction

        self.ax = ax
        self.visible = True
        self.canvas = ax.figure.canvas
        self.canvas.mpl_connect('motion_notify_event', self.onmove)
        self.canvas.mpl_connect('button_press_event', self.press)
        self.canvas.mpl_connect('button_release_event', self.release)
        self.canvas.mpl_connect('draw_event', self.update_background)

        self.rect = None
        self.background = None

        self.rectprops = rectprops
        self.onselect = onselect
        self.onmove_callback = onmove_callback
        self.useblit = useblit
        self.minspan = minspan

        # Needed when dragging out of axes
        self.buttonDown = False
        self.prev = (0, 0)

        if self.direction == 'horizontal':
            trans = blend_xy_sep_transform(self.ax.transData, self.ax.transAxes)
            w,h = 0,1
        else:
            trans = blend_xy_sep_transform(self.ax.transAxes, self.ax.transData)
            w,h = 1,0
        self.rect = Rectangle( (0,0), w, h,
                               transform=trans,
                               visible=False,
                               **self.rectprops
                               )

        if not self.useblit: self.ax.add_patch(self.rect)
        self.pressv = None