Named MetaPost instances

[jemmybutton]

In some cases it may be useful to have several named MetaPost instances which can be referred to independently from LaTeX (similar to what ConTeXt offers). As far as I understand, currently, this can't be achieved using luamplib? The interface could look something like:

\begin[instance_name]{mplibcode}
...
\end{mplibcode}

(see also this) My naïve attempt at implementing a minimal workaround does seem to work ok:

local function process_mplibcode_alt (data, instanceName)
  legacy_mplibcode_reset()

  local everymplib    = texgettoks'everymplibtoks'    or ''
  local everyendmplib = texgettoks'everyendmplibtoks' or ''
  data = format("\n%s\n%s\n%s\n",everymplib, data, everyendmplib)
  data = data:gsub("\r","\n")

  data = data:gsub("\\mpcolor%s+(.-%b{})","mplibcolor(\"%1\")")
  data = data:gsub("\\mpdim%s+(%b{})", "mplibdimen(\"%1\")")
  data = data:gsub("\\mpdim%s+(\\%a+)","mplibdimen(\"%1\")")

  data = data:gsub(btex_etex, function(str)
    return format("btex %s etex ", -- space
      luamplib.verbatiminput and str or protect_expansion(str))
  end)
  data = data:gsub(verbatimtex_etex, function(str)
    return format("verbatimtex %s etex;", -- semicolon
      luamplib.verbatiminput and str or protect_expansion(str))
  end)

  if not luamplib.verbatiminput then
    data = data:gsub("\".-\"", protect_expansion)

    data = data:gsub("\\%%", "\0PerCent\0")
    data = data:gsub("%%.-\n","")
    data = data:gsub("%zPerCent%z", "\\%%")

    run_tex_code(format("\\mplibtmptoks\\expanded{{%s}}",data))
    data = texgettoks"mplibtmptoks"
    data = data:gsub("##", "#")
    data = data:gsub("\".-\"", unprotect_expansion)
    data = data:gsub(btex_etex, function(str)
      return format("btex %s etex", unprotect_expansion(str))
    end)
    data = data:gsub(verbatimtex_etex, function(str)
      return format("verbatimtex %s etex", unprotect_expansion(str))
    end)
  end

  process_alt(data, instanceName)
end
...
local function process_alt (data, instanceName)
  local standalone = not luamplib.codeinherit
  local currfmt = instanceName or currentformat .. (luamplib.numbersystem or "scaled")
    .. tostring(luamplib.textextlabel) .. tostring(luamplib.legacy_verbatimtex)
  local mpx = mplibinstances[currfmt]
  if mpx and standalone then
    mpx:finish()
  end
  if standalone or not mpx then
    mpx = luamplibload(currentformat)
    mplibinstances[currfmt] = mpx
  end
  return process_indeed(mpx, data)
end

\directlua{luamplib.codeinherit = true}
\directlua{luamplib.process_mplibcode_alt([===[beginfig(1);a := 1cm;draw fullcircle scaled a;endfig;]===],"instance_a")}
\directlua{luamplib.process_mplibcode_alt([===[beginfig(1);a := 2cm;draw fullcircle scaled a;endfig;]===],"instance_b")}
\directlua{luamplib.process_mplibcode_alt([===[beginfig(1);draw unitsquare scaled a;endfig;]===],"instance_a")}
\directlua{luamplib.process_mplibcode_alt([===[beginfig(1);draw unitsquare scaled a;endfig;]===],"instance_b")}

But I'm sure it may break something elsewhere.

[jemmybutton]

I modified .sty and .lua files to work as described: luamplib_with_named_instances.zip

The following:

\mplibcodeinherit{enable}

\begin{mplibcode} % no instance name
beginfig(1);
a := 1/2cm;
draw fullcircle scaled a;
endfig;
\end{mplibcode}

\begin{mplibcode}[instance_one]
beginfig(1);
a := 1cm;
draw fullcircle scaled a;
endfig;
\end{mplibcode}

\begin{mplibcode}[instance_two]
beginfig(1);
a := 2cm;
draw fullcircle scaled a;
endfig;
\end{mplibcode}

\begin{mplibcode} % no instance name
beginfig(1);
draw unitsquare scaled a;
endfig;
\end{mplibcode}

\begin{mplibcode}[instance_one]
beginfig(1);
draw unitsquare scaled a;
endfig;
\end{mplibcode}

\begin{mplibcode}[instance_two]
beginfig(1);
draw unitsquare scaled a;
endfig;
\end{mplibcode}

produces this:

I didn't test it thoroughly though.

[dohyunkim]

Thanks for the suggestion. Would you please make a PR?

[jemmybutton]

@dohyunkim Sure! Done.

[dohyunkim]

Thank you so much. A new version based on your contribution has just been sent to CTAN.