Suppress rendering of empty canvas created by graphics device side-effects

[yjunechoe]

This concerns the side-effect of functions like grid::convertUnit() which requests information from the graphics device. If a graphics device is not available, R will open one as a side-effect. The issue concerns whether this then gets rendered as an image.

litedown will render an empty canvas in these cases:

In rmarkdown (and quarto), the rendering is suppressed:

I'm not sure how it's implemented in rmarkdown/quarto, but if it's not too much hassle I think this behavior is desirable to implement for litedown. Please LMK what you think!

---

Reprex:

f <- tempfile(fileext = ".Rmd")
writeLines("
---
title: reprex
---

```{r}
library(grid)
g <- pointsGrob()
x <- convertUnit(g$x, 'mm')
x
```
", f)
rmarkdown_html <- rmarkdown::render(f)
browseURL(rmarkdown_html)
litedown_html <- litedown::fuse(f)
browseURL(litedown_html)

[yihui]

I'll see if I can suppress this empty plot. In the mean time, you can use the chunk option fig.path = NULL to avoid capturing the plot on litedown's side: https://yihui.org/litedown/#sec:option-fig Thanks for the report!

[yjunechoe]

Thanks for the quick response!

Apologies if I'm misunderstanding, but fig.path = NULL doesn't seem to prevent the plot from being rendered for me. Am I doing this correctly?

---
knit: litedown:::knit
---

```{r, fig.path = NULL}
library(grid)
g <- pointsGrob()
x <- convertUnit(g$x, 'mm')
x
```

[yihui]

Sorry I meant fig.path = NA instead of NULL.

[yjunechoe]

Thanks, that worked!