Tikz Lua Filter for Pandoc

tikz.lua

local function draw_symbol(i,j,char)
   if char == '-' then
      return string.format('\\draw (%s,%s) -- (%s,%s)\n', i-1,j-0.5,i,j-0.5)
   elseif char == '_' then
      return string.format('\\draw (%s,%s) -- (%s,%s)\n', i-1,j,i,j)
   elseif char == '|' then
      return string.format('\\draw (%s,%s) -- (%s,%s)\n', i-0.5,j-1,i-0.5,j)
   elseif char == '/' then
      return string.format('\\draw (%s,%s) -- (%s,%s)\n', i-1,j-1,i,j)
   elseif char == '\\' then
      return string.format("\\draw (%s,%s) -- (%s,%s)\n", i-1,j-1,i,j)
   elseif char == '+' then
      return string.format('\\draw (%s,%s) -- (%s,%s)\n\\draw (%s,%s) -- \\draw (%s,%s)\n', i-1,j-0.5,i,j-0.5,i-0.5,j-1,i-0.5,j)
   elseif char == '<' then
      return string.format('\\draw [<-]  (%s,%s) -- (%s,%s)\n', i-1,j-0.5,i,j-0.5)
   elseif char == '>' then
      return string.format('\\draw [->]  (%s,%s) -- (%s,%s)\n', i-1,j-0.5,i,j-0.5)
   elseif char == '~' then
      return string.format('\\draw (%s,%s) -- (%s,%s)\n', i-0.75,j-0.5,i-0.25, j-0.5)
   elseif char ==  ':' then
      return string.format('\\draw (%s,%s) -- (%s,%s)\n \\draw (%s, %s) -- (%s,%s)', i-0.5,j-0.1,i-0.5, j-0.75, i-0.5, j-0.25, i-0.5, j)
   elseif char == 'v' then
      return string.format('\\draw [->] (%s,%s) -- (%s, %s)', i - 0.5, j-1, i-0.5,j)
   elseif char == '^' then
      return string.format('\\draw [<-] (%s,%s) -- (%s, %s)', i - 0.5, j-1, i-0.5,j)
   elseif char == "o" then
      return string.format('\\draw (%s,%s) circle [radius=1pt]' i-0.5,j-0.5)
   else
      error('Non-diagram character found: '..char)
   end
end



local function draw_tikz (diagram)
   local i = 1 -- length along a line
   local j = 1 -- line number
   local pos = 1 -- position in diagram string
   local tikz_final = '' -- what we will eventually output
   while pos <= diagram:len() do
      if diagram[pos] == '\n' then
	 local j = j+1
	 local i = 1
	 local pos = pos+1
      else
	 tikz_final = tikz_final..draw_symbol( i,j, diagram[pos])
	 pos = pos+1
      end
   end
   return '\\begin{tikzpicture}\n'..tikz_final..'\n\\end{tikzpicture}'
end


   


-- only use if going to latex
if FORMAT:match 'latex' then
   function Figure(elem) --use figure elements
      if elem.attr.Attributes['tikz'] == 'true' then -- require a tikz attribute
	 return pandoc.Figure { pandoc.Str draw_tikz(io.open(elem.content)), elem.caption, elem.attr } -- only modify content
      else
	 return elem
      end
   end
end