closes #436: use cairo_pdf() to record graphics

_posts/2011-12-09-graphics.md

@@ -75,6 +75,14 @@ list.files(system.file('enc', package = 'grDevices'))
 
 You probably need to set the encoding when you see a warning like this: `Warning: conversion failure on '<var>' in 'mbcsToSbcs': dot substituted for <var>`.
 
+Another possibility is to use the `cairo_pdf` device instead of `pdf` (see [#436](https://github.com/yihui/knitr/issues/436)):
+
+{% highlight r %}
+options(device = function(file, width = 7, height = 7, ...) {
+  cairo_pdf(tempfile(), width = width, height = height, ...)
+})
+{% endhighlight %}
+
 ## The Dingbats font
 
 According to the documentation of `pdf()`, the `useDingbats` argument can reduce the file size of PDF's which contain small circles. If you are using **knitr** in RStudio, this option is disabled by default. You may want to enable it by putting `pdf.options(useDingbats = TRUE)` in your source document if you have large scatter plots. See [#311](https://github.com/yihui/knitr/issues/311) for more comments and discussions.