[matplotlib-devel] transform question

Hi MPL transform gurus (aka Mike),

I'm trying to close on this "dropped spine" thing, and I have a question
I think you could save me some time on.

I need to get a transform that will be combined with the normal xaxis
transform to shift the spine and associated ticks and tick labels by
some amount. For my first incarnation, I used something like

mtransforms.ScaledTranslation(offset_x,offset_y,self.figure.dpi_scale_trans)

This is fine when I new the offset in points directly. However, now I'd
like to support offsetting the spine to the center of the Axes. So, for
this case, I'd like to calculate the offset transform required to take
axes coordinate 0 and translate it to 0.5. Thus, I think I need
something like

mtransforms.ScaledTranslation(0.5, 0, self.axes.transAxes)

Unfortunately, that's clearly not working. So, is there a quick fix for
this?

Note that, as I've implemented things, the easiest path is that the new
transform is a translation combined with the existing xaxis transform
(using "get_xaxis_transform() + my_new_transform"). Other methods may be
possible, but I think they'll be a lot more work.

Thanks,
Andrew