PanDoc filter to extract images from LaTeX with TikZ

tikz-to-png.lua

-- From: How to use PanDoc to derive output from LaTeX and TikZ to a DOCX file?
-- https://tex.stackexchange.com/questions/431719/how-to-use-pandoc-to-derive-output-from-latex-and-tikz-to-a-docx-file
-- see https://linuxtoosx.blogspot.com/2021/10/pandoc-quite-good-conversion-from-latex.html

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 -density 300  " .. tmp .. ".pdf " .. outfile)
  os.remove(tmp .. ".tex")
  os.remove(tmp .. ".pdf")
  os.remove(tmp .. ".log")
  os.remove(tmp .. ".aux")
end

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