如何在 knitr 中使用不同的 "dev.off()"（自动裁剪图形）

Question

我想在使用 knitr 转换为 PDF 的 .Rnw 文档中使用我自己的 pdf() 绘图设备。生成图的PDF后它应该调用 pdfCrop.off() 而不是 dev.off() （或任何 knitr 调用）；这个会完美裁剪生成的图形。这怎么能做到？

如果 (*) 被注释掉（以及正确关闭之前的行），则以下 MWE 工作（但没有裁剪）。

\documentclass{article}

\begin{document}
<<knitr_options, echo = FALSE, results = "hide", purl = FALSE>>=
## Custom graphics device (for cropping .pdf):
pdfCrop <- function(file, width, height, ...)
{
    f <- file
    grDevices::pdf(f, width = width, height = height, onefile = FALSE)
    assign(".pdfCrop.file", f, envir = globalenv())
}
pdfCrop.off <- function() # used automagically
{
    grDevices::dev.off() # closing the pdf device
    f <- get(".pdfCrop.file", envir = globalenv())
    system(paste("pdfcrop --pdftexcmd pdftex", f, f, "1>/dev/null 2>&1"),
           intern = FALSE) # crop the file (relies on PATH)
}

## knitr options
knitr::opts_chunk$set(fig.path = "./fig_", background = "#FFFFFF",
                      dev = "pdfCrop", fig.ext = "pdf") # (*) => how to use pdfCrop.off() instead of dev.off()?
@

<<MWE>>=
<<fig-MWE, eval = FALSE, echo = FALSE>>=
plot(1:10, 10:1)
@
\setkeys{Gin}{width=\textwidth}
\begin{figure}[htbp]
  \centering
  \framebox{
<<figMWE, echo = FALSE, fig.width=6, fig.height=6>>=
<<fig-MWE>>
@
}
\caption{Just some text to show the actual textwidth in order to see that the
  figure is not perfectly horizontally aligned due to some white space which can
  be avoided by properly crop the figure with an adequate pdf crop device.}
\end{figure}

\end{document}

Answer 1

knitr 已经提供了一个基于 pdfcrop 的裁剪设备，所以我们可以通过 hook 使用它：

\documentclass{article}

\begin{document}
<<knitr_options, echo = FALSE, results = "hide", purl = FALSE>>=
## knitr options
library(knitr)
knit_hooks$set(crop = hook_pdfcrop)
knitr::opts_chunk$set(fig.path = "./fig_", # all figures are saved as fig_*
                      background = "#FFFFFF", # avoid color
                      crop = TRUE) # always crop
@

<<MWE>>=
<<fig-MWE, eval = FALSE, echo = FALSE>>=
plot(1:10, 10:1)
@
\setkeys{Gin}{width=\textwidth}
\begin{figure}[htbp]
  \centering
<<figMWE, echo = FALSE, fig.width=6, fig.height=6>>=
<<fig-MWE>>
@
\caption{Just some text to show the actual textwidth in order to see that the
  figure is not perfectly horizontally aligned due to some white space which can
  be avoided by properly crop the figure with an adequate pdf crop device.}
\end{figure}

\end{document}

如何在 knitr 中使用不同的 "dev.off()"（自动裁剪图形）

How to use different "dev.off()" with knitr (to auto-crop figures)

knitr

rnw