• There is one point in the old implementation which I do not understand:

        if self._ticklabel_add_angle != self._axislabel_add_angle:
            if ((self.major_ticks.get_visible()  # ???
                 and not self.major_ticks.get_tick_out())
                or (self.minor_ticks.get_visible()
                    and not self.major_ticks.get_tick_out())):
                axislabel_pad = self.major_ticks._ticksize
            else:
                axislabel_pad = 0

My recollection is that this is to test if the axislabel and the ticklabels are on the same side. If self._ticklabel_add_angle != self._axislabel_add_angle is True, it means that they on different side. In this case, we only need to check if the ticks are on the same side as the axislabel. Also, the second branch of the or should use minor_ticks twice.

I just realized that this is a two-year old PR. It would be still good if this can be merged after some more fix. I can work on it if that is desired.

@leejjoon Feel free to pick it up; it was essentially a proof of concept in reply to #19101.
One thing I would suggest to change, though, is the orientation of ticks with the "out" direction: as noted above, I think it would look nicer if they were actually perpendicular to the box, rather than tangential with the gridline. (Inwards ticks can stay tangential.)

One thing I would suggest to change, though, is the orientation of ticks with the "out" direction: as noted above, I think it would look nicer if they were actually perpendicular to the box, rather than tangential with the gridline. (Inwards ticks can stay tangential.)

For this, I'd like to introduce tickangle_mode. For now, it's argument could be 'auto' (or None), 'normal', and 'parallel'. 'normal' is for perpendicular to the box, 'parallel' is for parallel to gridlines, and 'auto' is 'normal' only if tickdir is 'out'.

However, I don't think these are good choice of option names. Any recommendation?

Here are some exanples. For the floating_axis, I enforced "parallel" mode.

I would perhaps call this tick_orientation={"parallel", "normal", "auto"}. Perhaps @timhoffm can chime in?

Superseded by #24553.

Actually superseded by #30369 in the end.