Option to hide/ignore incremental slides

[sebpardo]

There does not seem to be an option in remark to ignore incremental slides separators when converting to html. This is particularly desirable when converting html to pdf to produce slide notes. While there is already a request for this feature in the remark repo (gnab/remark#478), I think this could be easily implemented in xaringan by parsing the Rmd file to remove the -- delimiters before moon_readering to a temporary html, and finally converting to pdf using decktape. I use something along these lines in a Makefile using sed:

sed '/^--$$/d' slides.Rmd > temp.Rmd 
Rscript -e "library(rmarkdown); render('temp.Rmd', 'xaringan::moon_reader')"
decktape remark --chrome-arg=--allow-file-access-from-files temp.html slides.pdf

Perhaps this could be easily implemented in xaringan/R using a text parser?

[yihui]

I think @benjie's solution there is more robust and also has the advantage of letting you both view and print the slides with the same HTML page, so I'll integrate it into this package. Of course, I wish remark.js could support it officially.

The problem with sed '/^--$$/d' is that not all -- mean separators, e.g., -- in a code block:

```
--
```

I actually want this feature myself, too, so thanks for the report!

[yihui]

Done. You may test https://slides.yihui.name/xaringan/.

remotes::install_github('yihui/xaringan')

[sebpardo]

The slides print to pdf without the incremental slides as expected when using the Chromium -> print to PDF method, but unfortunately this method still has many issues which have previously been reported (e.g. not showing italics/bold text, LaTeX math, etc.). As is to be expected, the decktape method is unchanged.

I have minimal knowledge of CSS and JS, so perhaps what I'm going to suggest won't make much sense, but I'll give it a shot anyways :-) Looking at the hack written by @benjie it seems there should be a way of adding a CSS theme to enable hiding incremental slides when moon reading. Could adding has-continuation to all incremental slides but the last be done automatically, but the @media print { .has-continuation { display: none; } } trigger also be delivered via a CSS theme that can be specified in the Rmd's YAML for rendering to html rather than printing? This way we could potentially adapt this method for converting to pdf using decktape, with works much better than Chromium for complex slides.

[yihui]

I'm not sure if I get it: are you saying the fix doesn't work for decktape?

BTW, I have just fixed the several issues related to Chrome printing (MathJax, italics/bold text, ...). I think Chrome should work reasonably well with the current development version of xaringan.

[sebpardo]

Yes, sorry about that. Converting to pdf with decktape() still results in separate pages for incremental slides when docker = FALSE. I don't have docker installed so I'm unable to try to convert through it.

That's great about the fixes related to Chrome printing! Will test things again with the latest dev version. Thanks again!

[yihui]

I see. It is unfortunate that decktape does not respect display: none in this case. As I said, simply deleting ^--$ from the Markdown source is not a robust solution, so I tend not to use it if possible.

[pat-s]

Which decktape version did you use? I can give it a shot later.

[sebpardo]

@pat-s I used decktape v2.9.1.

[yihui]

In fact, in the development version of remark.js, there is an option to disable incremental slides entirely: gnab/remark@40e69d21580

And a CSS class remark-slide-incremental will also be added: gnab/remark@29515556

That said, I have no idea when the next version of remark.js will be released: gnab/remark#548 (comment).