Unneeded warnings when creating plot using non-default fonts

[yixuan]

Take this code snippet as an example (assuming "Ubuntu" font is installed in the system):

\documentclass{article}
\begin{document}

<<dev='png'>>=
library(ggplot2)
ggplot() + geom_point(aes(x=mpg, y=wt), data=mtcars) +
    theme(text = element_text(size = 16, family = "Ubuntu"))
@

\end{document}

When compiling this with knitr, the output pdf will contain a long list of warnings similar as below:

## Warning: font family 'Ubuntu' not found in PostScript font database

However, if we call the device function directly,

png()
library(ggplot2)
ggplot() + geom_point(aes(x=mpg, y=wt), data=mtcars) +
    theme(text = element_text(size = 16, family = "Ubuntu"))
dev.off()

then there is no such warning issued.

I believe this is caused by the null graphics device pdf(NULL). From my understanding knitr will evaluate code chunk on this null device and record the plotting operations to some objects. However, pdf() only support standard fonts like "Times" and "Courier", and will yell to other fonts that it does not recognize.

The "real" null device mentioned in http://yihui.name/en/2010/12/a-special-graphics-device-in-r-the-null-device/ is already removed from R. Is there any other approach to solve this problem?

[yihui]

#561 may be one approach, but I have not implemented it yet.

An inelegant solution is to set the recording device to png, e.g.

options(device = function(file, width, height) {
  png(tempfile(), width = width, height = height)
})

Maybe I should give up the idea of using the PDF null device to record graphics, but use the device specified in the dev option instead. I'll think more about this.

[hrbrmstr]

possibly also solved by using extrafont::loadfonts() in a hidden markdown block?

[yihui]

I think this specific problem has been solved long ago. When dev='png', knitr will just use a png() device to record plots instead of the null pdf() device.

[bhaskarvk]

FWIW I am still seeing this bug and I do need to use the workaround mentioned in #729 (comment)

[JerryWho]

I still have this problem, too. My problem isn't resolved with this work around. The work around seems only to work with pdflatex or lualatex. But I habe to use xelatex.
With xelatex there aren't any fonts in the graphics.
This document only gets this output

\documentclass{article}
\usepackage{graphicx}

\begin{document}
<<set-options>>=
 Sys.setenv(LANG = "en")  
 options(device = function(file, width, height) {
  png(tempfile(), width = width, height = height)
})
@
 \begin{figure}
    \centering
<<output, dev='png'>>=
library(ggplot2)
ggplot(mtcars, aes(x=wt, y=mpg, color=factor(gear))) + geom_point() +
 ggtitle('Fuel Efficiency of 32 Cars') +
 xlab('Weight (x1000 lb)') + ylab('Miles per Gallon') +
 theme(text=element_text(size=16, family='Source Code Pro'
 ))
@
   \end{figure}


\end{document}

(I'm using an extra example because I'm using a Mac and don't have this Ubuntu font. So I use Source Code Pro.)

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