Get the transformation used for drawing x-axis labels, which will add the given amount of padding (in points) between the axes and the label. The x-direction is in data coordinates and the y-direction is in axis coordinates. Returns a 3-tuple of the form:
(transform, valign, halign)
where valign and halign are requested alignments for the text.
This transformation is primarily used by the
Axis class, and is meant to be
overridden by new kinds of projections that may need to
place axis elements in different locations.