mtext truncates plot region in classic theme

[bastistician]

In the classic theme, adding extra axis labels using mtext seems to truncate the plot region.

First mtext then abline:

plt(0, 0, theme = "classic")
mtext("foo", at=0.3, side=2, line=2, las=1)
abline(h = 0.3)  # does NOT reach the y-axis

First abline then mtext:

plt(0, 0, theme = "classic")
abline(h = 0.3)  # OK
mtext("foo", at=0.3, side=2, line=2, las=1)

[grantmcdermott]

Unfortunately, this is a hard limitation of our ephemeral theme logic, since we (a) automatically reset the pars on exit and (b) can't plug into subsequent base graphics layers (like abline and mtext) that we don't control.

Three potential workarounds:

1. Set a persistent theme:

tinytheme("classic")
plt(0, 0)
mtext("foo", at=0.3, side=2, line=2, las=1)
abline(h = 0.3)
tinytheme() # reset theme (optional)

2. Keep the ephemeral theme, but pass the additional layers through draw (so that they're drawn as part of the same plt call):

plt(
  0, 0, theme = "classic",
  draw = {
    mtext("foo", at=0.3, side=2, line=2, las=1)
    abline(h = 0.3)
  }
)

3. Keep the ephemeral theme, but switch to layering with idiomatic plt_add equivalents:

plt(0, 0, theme = "classic")
plt_add(type = type_hline(0.3))
plt_add(par("usr")[1], y = 0.3, type = type_text(labels = "foo", xpd = NA, pos = 2))

Personally, I'd probably reach for option 2 as the most natural. But that's also b/c I have a preference for ephemeral themes (plus the fact that draw also plays nicely with the file = <myplot.png> arg).

Let us know if these address your issue.

[bastistician]

Thank you for the detailed reply (and sorry for my late one).

• The draw (aka panel.first) option is really nice to have, but I would not use it in my actual code as I add several more elements to the initial plot and I don't like to put too much into this argument.

• The plt_add equivalents are a bit too verbose for my taste.
  They also do not seem to solve the truncation when adding the line after the text:

plt(0, 0, theme = "classic")
plt_add(par("usr")[1], y = 0.3, type = type_text(labels = "foo", xpd = NA, pos = 2))
plt_add(type = type_hline(0.3))  # does NOT reach the y-axis

• Switching the theme globally and switching back afterwards seems to be the best option. This currently requires knowing the original theme to revert to. I tried

otheme <- tinytheme("classic")
# ...
tinytheme(otheme)

but tinytheme returns NULL, so this always restores the default theme.

[grantmcdermott]

Thanks for the follow-up! Both addressed in #738.