%D \module
%D   [       file=anch-snc,
%D        version=2003.12.01, % actually 1999 so real old
%D          title=\CONTEXT\ Anchoring Macros,
%D       subtitle=Synchronization,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA ADE \& \CONTEXT\ Development Team}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

%D This is a rather old mechanism that we once needed in an actually nice design.
%D Those were the times that processing a rather complex xml file with \PDFTEX\ into
%D a 400 page document took 45 minutes (a few runs) while nowadays with luatex and
%D \MKIV\ (and \LMTX) we express runtime in seconds.
%D
%D In retrospect it was a waste of time (and money) to invest in all these
%D mechanisms because the publishers we were dealign with were far from ready for
%D dealing with xml and let alone automatic rendering. But, as the code still worked
%D well after nearly two decades I decided to revive it .. maybe some curious
%D \CONTEXT\ user can benefit from it after all.
%D
%D The logic is mostly the same as in \MKII\ but some work is now delegated to \LUA\
%D so that we save memory and gain some runtime. As this was not really a used
%D module the interface also was upgraded. As we know the bottlenecks in \METAPOST\
%D we also work around those a bit. It made sense too change the interface to use
%D the new \LMTX\ mechanisms for passing parameters. The old interface can be found
%D in the \MKII\ and \MKIV\ files.

%D TODO: bleed | autobleed

\writestatus{loading}{ConTeXt Anchoring Macros / Synchronization}

\registerctxluafile{anch-snc}{}
\registerctxluafile{mlib-snc}{}

%D \stoptyping
%D \starttext
%D
%D \setuplayout[location=middle]
%D \setupbodyfont[dejavu]
%D
%D \definesyncpositions[1]
%D \definesyncpositions[2]
%D
%D % \startuseMPgraphic{sync1}
%D %     StartPage ;
%D %         lmt_synchronizer [ ... ] ;
%D %         clip currentpicture to Page ;
%D %         setbounds currentpicture to Page ;
%D %     StopPage ;
%D % \stopuseMPgraphic
%D
%D \startuseMPgraphic{sync1}
%D     lmt_synchronizer [
%D       % page       = "yes",
%D         index      = 1,
%D         hoffset    = 0,
%D         width      = BackSpace - LeftMarginDistance,
%D         extend     = false,
%D         prune      = true,
%D         draw       = false,
%D         fill       = true,
%D     ] ;
%D \stopuseMPgraphic
%D
%D \startuseMPgraphic{sync2}
%D     lmt_synchronizer [
%D         index   = 2,
%D         region  = OverlayRegion,
%D         hoffset = -1cm,
%D         width   = 1cm,
%D         extend  = true,
%D         prune   = false,
%D         draw    = false,
%D         fill    = true,
%D     ] ;
%D     clip currentpicture to OverlayBox leftenlarged 1cm;
%D     setbounds currentpicture to OverlayBox ;
%D \stopuseMPgraphic
%D
%D \defineoverlay[tempoverlay1][\useMPgraphic{sync1}]
%D \defineoverlay[tempoverlay2][\useMPgraphic{sync2}]
%D
%D \setupbackgrounds[page][background=tempoverlay1]
%D
%D \framed[region=yes,background=tempoverlay2,width=14cm,align=normal]{%
%D     \syncposition[2][1]\samplefile{ward}\endgraf
%D     \syncposition[2][2]\samplefile{ward}\endgraf
%D     \syncposition[2][3]\samplefile{ward}\endgraf
%D }
%D
%D \vskip1cm \hskip1cm \framed[region=yes,background=tempoverlay2,width=16cm,align=normal]{%
%D     \syncposition[2][1]\samplefile{ward}\endgraf
%D     \syncposition[2][2]\samplefile{ward}\endgraf
%D     \syncposition[2][3]\samplefile{ward}\endgraf
%D }
%D
%D \vskip1cm \hskip1cm \framed[region=yes,background=tempoverlay2,width=10cm,align=normal]{%
%D     \syncposition[2][1]\samplefile{ward}\endgraf
%D     \syncposition[2][2]\samplefile{ward}\endgraf
%D     \syncposition[2][3]\samplefile{ward}\endgraf
%D }
%D
%D \dorecurse {100} {
%D     \startchapter[title={Test #1}]
%D         \syncposition[1][1,reset]\dorecurse{20}{\samplefile{ward}\endgraf}
%D         \syncposition[1][2]\dorecurse {4}{\samplefile{ward}\endgraf}
%D         \syncposition[1][3]\dorecurse {7}{\samplefile{ward}\endgraf}
%D         \syncposition[1][4]\dorecurse {3}{\samplefile{ward}\endgraf}
%D     \stopchapter
%D }
%D
%D \dorecurse {100} {
%D     \startchapter[title={Test #1}]
%D         \syncposition[1][1]\dorecurse{1}{\samplefile{ward}\endgraf}
%D         \syncposition[1][2]\dorecurse{1}{\samplefile{ward}\endgraf}
%D         \syncposition[1][3]\dorecurse{1}{\samplefile{ward}\endgraf}
%D         \syncposition[1][4]\dorecurse{1}{\samplefile{ward}\endgraf}
%D     \stopchapter
%D }
%D
%D \stoptext
%D \stoptyping

%D We could actually use par positions but in \LMTX\ we have syncpos entries
%D somewhat optimized.

\unprotect

\installcorenamespace{syncposcounter}

\let\c_sync_n\relax

\permanent\protected\def\definesyncpositions[#1]%
  {\ifcsname\??syncposcounter:#1\endcsname \else
     \expandafter\newinteger\csname\??syncposcounter:#1\endcsname
   \fi}

\permanent\tolerant\protected\def\syncposition[#1]#*[#2]%
  {\dontleavehmode
   \ifcsname\??syncposcounter:#1\endcsname
     \let\c_sync_n\lastnamedcs
     \global\advanceby\c_sync_n\plusone
     \enabletextarearegistration
     \setpositionplus{\s!syncpos:#1:\the\c_sync_n}{#2}\hpack{\strut}%
   \else
     \strut
   \fi
   \ignorespaces}

\protect