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

[Jan van der Laan]

Someone asked for the response I got from CRAN. I included it below:

---
[... another issue where I forgot a \value{} in the documentation of one 
of the functions]

Please make sure that you do not change the user's options, par or 
working directory. If you really have to do so within functions, please 
ensure with an *immediate* call of on.exit() that the settings are reset 
when the function is exited.
e.g.:
...
oldpar <- par(no.readonly = TRUE) # code line i
on.exit(par(oldpar)) # code line i + 1
...
par(mfrow=c(2,2)) # somewhere after
...
e.g.: -> R/tgp.R
If you're not familiar with the function, please check ?on.exit. This 
function makes it possible to restore options before exiting a function 
even if the function breaks. Therefore it needs to be called immediately 
after the option change within a function.
For more details: 
<https://contributor.r-project.org/cran-cookbook/code_issues.html#change-of-options-graphical-parameters-and-working-directory>

Please fix and resubmit.
---

I understand why this is asked and I also know how to handle this in 
usual cases. I am not sure how to handle this in the specific case here. 
Perhaps I missed some alternative way of handling this.

Best,
Jan


On 8/20/25 21:31, Jan van der Laan wrote:
> 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
> 
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