How to use pandoc to convert .tex file, containing a TikZ figure, to a .docx file?

Question

What I want to do is to convert a .tex file, containing several TikZ figures to a .docx-file using pandoc. I have tried to follow the pandoc documentation and to use lua filters to achieve this. Problem: whenever I use the lua filter, a file is generated that contains only the title of my .tex file and all the rest of the file is omitted. I do not see the TikZ figures either.

This is my input for pandoc in the commandline:

 pandoc --from latex+raw_tex --lua-filter=tikz.lua -s file.tex -o test.docx

My lua filter file (tikz.lua) is changed from the original filter suggested by pandoc, on the basis of the advice given in this post. I have adopted the suggested changes there one-on-one to this file:

local function file_exists(name)
  local f = io.open(name, 'r')
  if f ~= nil then io.close(f); return true
  else return false end
end

function RawBlock(el)
  -- Don't alter element if it's not a tikzpicture environment
  if not el.text:match'^\\begin{tikzpicture}' then
    return nil
    -- Alternatively, parse the contained LaTeX now:
    -- return pandoc.read(el.text, 'latex').blocks
  end  
  local fname = pandoc.sha1(el.text) .. ".png"
  if not file_exists(fname) then
    tikz2image(el.text, fname)
  end
  return pandoc.Para({pandoc.Image({}, fname)})
end

--- Create a standalone LaTeX document which contains only the TikZ picture.
--- Convert to png via Imagemagick.
local function tikz2image(src, outfile)
  local tmp = os.tmpname()
  local tmpdir = string.match(tmp, "^(.*[\\/])") or "."
  local f = io.open(tmp .. ".tex", 'w')
  f:write("\\documentclass{standalone}\n")
  -- include all packages needed to compile your images
  f:write("\\usepackage{tikz}\n\\usepackage{stanli}\n")
  f:write("\\begin{document}\n")
  f:write(src)
  f:write("\n\\end{document}\n")
  f:close()
  os.execute("pdflatex -output-directory " .. tmpdir  .. " " .. tmp)
  os.execute("convert " .. tmp .. ".pdf " .. outfile)
  os.remove(tmp .. ".tex")
  os.remove(tmp .. ".pdf")
  os.remove(tmp .. ".log")
  os.remove(tmp .. ".aux")
end

pdflatex and pdf2svg are both installed, as well as ImageMagick.

In short, I should be good to go but something goes wrong and all I see is my title. Any advice would be really welcome!

Here is my code:

\documentclass{book}

\usepackage{graphicx}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,positioning}

\begin{document}

\begin{tikzpicture}

\draw (0,0) -- (4,0);

\end{tikzpicture}

\end{document}

When rendering as a .pdf file in TexStudio, the TikZ figure shows up. When using pandoc, nothing happens.

Hopefully you can spot something I have missed!

Answer 1

The filter throws an error, because convert doesn't like to make a grey scale PNG. The solution is to add the option -colorspace RGB. In the end ImageMagick seems to have other issues too, so I suggest using pdftoppm -png form the poppler tools instead:

local function file_exists(name)
  local f = io.open(name, 'r')
  if f ~= nil then io.close(f); return true
  else return false end
end

--- Create a standalone LaTeX document which contains only the TikZ picture.
--- Convert to png via Imagemagick.
local function tikz2image(src, outfile)
  local tmp = os.tmpname()
  local tmpdir = string.match(tmp, "^(.*[\\/])") or "."
  -- local tmpdir = "."
  local f = io.open(tmp .. ".tex", 'w')
  f:write("\\documentclass{standalone}\n")
  -- include all packages needed to compile your images
  f:write("\\usepackage{tikz}\n\\usepackage{stanli}\n")
  f:write("\\begin{document}\n")
  f:write(src)
  f:write("\n\\end{document}\n")
  f:close()
  os.execute("pdflatex -output-directory " .. tmpdir  .. " " .. tmp)
  -- os.execute("convert " .. tmp .. ".pdf " .. "-colorspace RGB " .. outfile)
  os.execute("pdftoppm -png " .. tmp .. ".pdf " .. "> " .. outfile)
  os.remove(tmp .. ".tex")
  os.remove(tmp .. ".pdf")
  os.remove(tmp .. ".log")
  os.remove(tmp .. ".aux")
end

function RawBlock(el)
  -- Don't alter element if it's not a tikzpicture environment
  if not el.text:match'^\\begin{tikzpicture}' then
    return nil
    -- Alternatively, parse the contained LaTeX now:
    -- return pandoc.read(el.text, 'latex').blocks
  end  
  local fname = pandoc.sha1(el.text) .. ".png"
  if not file_exists(fname) then
    tikz2image(el.text, fname)
  end
  return pandoc.Para({pandoc.Image({}, fname)})
end

If you are using more complex tikz code, don't forget to add the used libraries and packages to the filter

---

You can also extend the original filter to cover .docx:

local system = require 'pandoc.system'

local tikz_doc_template = [[
\documentclass{standalone}
\usepackage{xcolor}
\usepackage{tikz}
\begin{document}
\nopagecolor
%s
\end{document}
]]

local function tikz2image(src, filetype, outfile)
  system.with_temporary_directory('tikz2image', function (tmpdir)
    system.with_working_directory(tmpdir, function()
      local f = io.open('tikz.tex', 'w')
      f:write(tikz_doc_template:format(src))
      f:close()
      os.execute('pdflatex tikz.tex')
      if filetype == 'pdf' then
        os.rename('tikz.pdf', outfile)
      elseif filetype == 'png' then
        os.execute("pdftoppm -png tikz.pdf > " .. outfile)
      else
        os.execute('pdf2svg tikz.pdf ' .. outfile)
      end
    end)
  end)
end

extension_for = {
  docx = 'png',
  html = 'svg',
  html4 = 'svg',
  html5 = 'svg',
  latex = 'pdf',
  beamer = 'pdf' }

local function file_exists(name)
  local f = io.open(name, 'r')
  if f ~= nil then
    io.close(f)
    return true
  else
    return false
  end
end

local function starts_with(start, str)
  return str:sub(1, #start) == start
end


function RawBlock(el)
  if starts_with('\\begin{tikzpicture}', el.text) then
    local filetype = extension_for[FORMAT] or 'svg'
    local fname = system.get_working_directory() .. '/' ..
        pandoc.sha1(el.text) .. '.' .. filetype
    if not file_exists(fname) then
      tikz2image(el.text, filetype, fname)
    end
    return pandoc.Para({pandoc.Image({}, fname)})
  else
   return el
  end
end

---

Using it with the following document:

\documentclass{book}

\usepackage{graphicx}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,positioning}

\begin{document}

\begin{tikzpicture}

\draw[fill] (1,2) circle (100pt);

\end{tikzpicture}

\end{document}

On the command line:

pandoc --from latex+raw_tex --lua-filter=tikz.lua -s file.tex -o test.docx