def METHOD_NAME(self):
    """Returns a tuple of (x1, x2) screen space coordinates of the start
    and end selection points.
    If there is no current selection, then returns None.
    """
    ds = getattr(self.plot, self.axis)
    selection = ds.metadata[self.metadata_name]
    # "selections" metadata must be a tuple
    if self.metadata_name == "selections":
        if selection is not None and len(selection) == 2:
            return [self.mapper.map_screen(numpy.array(selection))]
        else:
            return []
    # All other metadata is interpreted as a mask on dataspace
    else:
        ar = numpy.arange(0, len(selection), 1)
        runs = arg_find_runs(ar[selection])
        coords = []
        for inds in runs:
            start = ds._data[ar[selection][inds[0]]]
            end = ds._data[ar[selection][inds[1] - 1]]
            coords.append(self.map_screen(numpy.array((start, end))))
        return coords