use cairo by default for bitmap devices if possible (rstudio/rmarkdow…

…n#2561)

NEWS.md

@@ -2,6 +2,8 @@
 
 - Added back/forward/refresh/print buttons to the toolbar in the `litedown::roam()` preview interface.
 
+- Set `options(bitmapType = 'cairo')` in `fuse()` if `capabilities('cairo')` is TRUE, which will generate smaller bitmap plot files (e.g., `.png`) than using `quartz` or `Xlib`, and is also a safer option for `fuse()` to be executed in parallel (rstudio/rmarkdown#2561).
+
 # CHANGES IN litedown VERSION 0.2
 
 - A data frame (or matrix/tibble) wrapped in `I()` is fully printed to a table now by default. Without `I()`, data objects are truncated to 10 rows by default when printing to tables.

R/fuse.R

@@ -528,8 +528,12 @@ fiss = function(input, output = '.R', text = NULL) {
     )
     message('Quitting from ', get_loc(nms[k]))
   }
-  # suppress tidyverse progress bars
-  opt = options(rstudio.notebook.executing = TRUE)
+  # suppress tidyverse progress bars and use cairo for bitmap devices (for
+  # smaller plot files and possible parallel execution)
+  opt = options(
+    rstudio.notebook.executing = TRUE,
+    bitmapType = if (capabilities('cairo')) 'cairo' else .Options$bitmapType
+  )
   on.exit({ options(opt); on_error() }, add = TRUE)
 
   # the chunk option `order` determines the execution order of chunks