filter module: call function before calling the filter command?

[Henning Hraban Ramm <texml@fiee.net>]

Ahoi!

As you probably know ;), I’m using the filter module with LilyPond, setup see below.

Now, I’d like to overwrite "texsettings.ly", containing the setting of ConTeXt’s text width, each time before I call LilyPond, to adapt its note line width to the current text width. That would automate the line width adaption to e.g. columns.

In the module’s documentation under "Dealing with expansion" I found the example of creating the filter command in a macro.
Can I use this to call a Lua function first and then LilyPond? Or is there a better way?


-----

\usemodule[filter]

\startbuffer[lilypond::settings]
\include "../lilysettings.ly" % file must be in same folder as text, not in lilytemp
\include "texsettings.ly"
\stopbuffer

\def\LILYTEMP{lilytemp} % name of folder for LilyPond/buffer files

\def\ParseLilypondFile#1% #1 is the name of the output file
  {\ctxlua{thirddata.parselilypondfile("#1")}}

\startluacode

 thirddata = thirddata or {}
 
 -- create temp folder if missing
 if not lfs.isdir("\LILYTEMP") then
   lfs.mkdir("\LILYTEMP")
 end

 -- write text width to include file
 io.savedata("\LILYTEMP/texsettings.ly", "\\paper { line-width = " .. 
 	string.gsub(number.topoints(tex.dimen.textwidth),"pt","\\pt") .. " } \n")
 
 function thirddata.parselilypondfile(name)
   -- include all systems (pages)
   -- name is like \LILYTEMP/mainfile-temp-lilypond-21.pdf
   logs.report("LILYPOND","name='" .. name .. "'")
   local scname = string.gsub(name, '%.pdf$', '-systems.count')
   local syco = tonumber(io.loaddata(scname)) or 0
   
   for nr = 1, syco do
     logs.report("LILYPOND","including system no." .. nr)
     context("\\externalfigure[" .. string.gsub(name, '%.pdf$', '-' .. nr) .. "]")
   end
 end
\stopluacode

\defineexternalfilter[lilypond]
	[continue=yes,
	cache=yes,
	%purge=no,
	readcommand=\ParseLilypondFile,
	bufferbefore={lilypond::settings},
	directory=\LILYTEMP/,
	output={\externalfilterbasefile.pdf},
	filtercommand={lilypond -dbackend=eps -dinclude-eps-fonts -dno-gs-load-fonts -o"\LILYTEMP/\externalfilterbasefile" "\externalfilterinputfile"}]

\starttext

-----



Greetlings, Hraban
---
http://www.fiee.net
http://wiki.contextgarden.net
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