LaTeX Source Code Blocks in Org Mode

LaTeX source code blocks set default values for two standard header arguments. In addition, several LaTeX-specific header arguments are defined to control creation of bitmap images and pdf snippets.

LaTeX does not support sessions.

The default result type is latex, which wraps the results in a #+BEGIN_LaTeX ... #+END_LaTeX block.

LaTeX source code blocks are a special case because their functionality largely overlaps with the export facilities in Org Mode.

At its simplest, Org Mode evaluation of LaTeX source code blocks with C-c C-c wraps the results in a #+BEGIN_LaTeX ... #+END_LaTeX block.

#+name: hello-world
#+BEGIN_SRC latex
\LaTeX
#+END_SRC

#+RESULTS: hello-world
#+BEGIN_LaTeX
\LaTeX
#+END_LaTeX

This complex example was posted to the Org Mode list by Andreas Leha. It depends on a working installation of the R statistical software.⁶ The code makes use of R sessions to preserve state between R source code blocks.

The first source code block loads the TikZ package, which defines a language to produce vector graphics from a geometric/algebraic description.

library("tikzDevice")

A simple plot is generated and output as LaTeX code by the TikZ device in R.

tikz(console=TRUE, width=4, height=4)
plot(rnorm(100), rnorm(100))
dummy <- dev.off()

The LaTeX output of this R code is processed by a LaTeX source code block, using Org Mode's noweb syntax. Note the various #+header: lines and their settings, which serve to configure ImageMagick. In this case, a png file is being produced outside the usual Org Mode path through dvipng. Note that the header presented here has been simplified somewhat. Interested readers might want to review Andreas' original post.

#+name: test_plot_png
#+header: :exports results :file test.png 
#+header: :imagemagick yes :iminoptions -density 600 :imoutoptions -geometry 400 
#+header: :fit yes :noweb yes :headers '("\\usepackage{tikz}")
#+begin_src latex :exports results :file test.png 
  <<test_plot()>>
#+end_src

With this header, the LaTeX output of the TikZ device in R yields a graph of the random number generation.

If the header is changed so the results are not written to a file, then the LaTeX code generated by the TikZ device is written to the Org Mode buffer. The results shown below have been shortened somewhat for illustrative purposes.

#+name: test_plot_tikz
#+begin_src latex :noweb yes :exports results
  <<test_plot()>>
#+end_src

#+BEGIN_LaTeX
% Created by tikzDevice version 0.6.2 on 2012-02-08 21:28:07
% !TEX encoding = UTF-8 Unicode
\begin{tikzpicture}[x=1pt,y=1pt]
\definecolor[named]{drawColor}{rgb}{0.00,0.00,0.00}
\definecolor[named]{fillColor}{rgb}{1.00,1.00,1.00}
\fill[color=fillColor,fill opacity=0.00,] (0,0) rectangle (289.08,289.08);
\begin{scope}
\path[clip] ( 49.20, 61.20) rectangle (263.88,239.88);
\definecolor[named]{drawColor}{rgb}{0.00,0.00,0.00}
\draw[color=drawColor,line cap=round,line join=round,fill opacity=0.00,] (184.34, 99.14) circle (  2.25);

...

\draw[color=drawColor,line cap=round,line join=round,fill opacity=0.00,] (143.44,134.70) circle (  2.25);
\end{scope}
\begin{scope}
\path[clip] (  0.00,  0.00) rectangle (289.08,289.08);
\definecolor[named]{drawColor}{rgb}{0.00,0.00,0.00}

\draw[color=drawColor,line cap=round,line join=round,fill opacity=0.00,] ( 75.29, 61.20) -- (250.80, 61.20);

\draw[color=drawColor,line cap=round,line join=round,fill opacity=0.00,] ( 49.20, 61.20) --

: (263.88, 61.20) – : (263.88,239.88) – : ( 49.20,239.88) – : ( 49.20, 61.20);

\end{scope}
\begin{scope}
\path[clip] (  0.00,  0.00) rectangle (289.08,289.08);
\definecolor[named]{drawColor}{rgb}{0.00,0.00,0.00}

\node[color=drawColor,anchor=base,inner sep=0pt, outer sep=0pt, scale=  1.00] at (156.54, 13.20) {rnorm(100)};

\node[rotate= 90.00,color=drawColor,anchor=base,inner sep=0pt, outer sep=0pt, scale=  1.00] at ( 13.20,150.54) {rnorm(100)};
\end{scope}
\end{tikzpicture}
#+END_LaTeX

This example demonstrates the handling of a LaTeX code block differently depending on the export backend. If the following file is exported to HTML the tikz code block will be converted to an SVG images, while on export to pdf (through LaTeX) the tikz code will simply be inserted into the document verbatim.

#+LATEX_HEADER: \usepackage{tikz}

First execute the second code block, to define the convenience macro
and to set the required new variables in ob-latex.el.  Then export to
HTML and to pdf to see the tree exported as an SVG image and as
embedded tikz respectively.

* Tikz test
Here's a tree, exported to both html and pdf.

#+header: :file (by-backend (html "tree.svg") (t 'nil))
#+header: :imagemagick
#+header: :results (by-backend (pdf "latex") (t "raw"))
#+begin_src latex
  \usetikzlibrary{trees}
  \begin{tikzpicture}
    \node [circle, draw, fill=red!20] at (0,0) {1}
    child { node [circle, draw, fill=blue!30] {2}
      child { node [circle, draw, fill=green!30] {3} }
      child { node [circle, draw, fill=yellow!30] {4} }};
  \end{tikzpicture}
#+end_src

* COMMENT setup
#+begin_src emacs-lisp :results silent
  (setq org-babel-latex-htlatex "htlatex")
  (defmacro by-backend (&rest body)
    `(case (if (boundp 'backend) (org-export-backend-name backend) nil) ,@body))
#+end_src

This allows for the automatic composition of beautiful scalable graphics across both HTML and pdf from a single document and image source.