[R-pkg-devel] Issue with use of par() in package

[Jan van der Laan]

I recently submitted a package to CRAN that creates a device that 
outputs into the terminal (for terminals that support the Terminal 
Graphics Protocol (and hopefully in the future also terminals that 
support sixel)) [1].

It introduces a 'tgp' function that does the following:

1. It opens a ragg::agg_capture device.

2. When term_col = TRUE: sets the background and foreground colors of 
the device to those of the terminal (when these can be detected).

3. Every time the ragg:agg_capture device is updated: updates the plot 
in the terminal.

Point 2 raises an issue from CRAN as par() changes some properties and 
these are not set back at the and of the function call. This is 
intentional, as otherwise setting them would be useless; it is the 
intention that the colors of subsequent plot calls are changed.  I am 
not sure how I can set the colors of the device to those in the terminal 
(as requested by the user) without violating this rule.

Are there alternative ways of helping the user to set the colors of the 
device without violating this issue?

Could this be an exception to the rule as the argument intentionally 
changes par()? This could be made more explicit by changing the default 
value to FALSE. I guess this question is better asked at the CRAN 
maintainers, but perhaps there are other package that do something 
similar that I might look at.

Instead of having this functionality in the tgp() function, I could 
create a 'set_figure_colours_to_terminal()` function (perhaps with a 
corresponding reset function). However, this function would run into the 
same issue.

I appreciate any suggestions/help that yoy could give.

Best,
Jan




[1] The current version of the code can be found here: 
https://codeberg.org/djvanderlaan/terminalgraphics/src/branch/dev