%D \module
%D   [       file=anch-pgr, % split off core-pos
%D        version=1999.08.01,
%D          title=\CONTEXT\ Anchoring Macros,
%D       subtitle=Positioning Graphics,
%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.

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

%D Before we come to graphics support, we have to make sure of
%D the reference point on the page. The next macros do so and
%D are hooked into the page building routine.

\unprotect

%D Here we implement position actions (was a dummy).

\unexpanded\def\showanchor#1%
  {\normalexpanded{\writestatus{#1}
     {\MPp{#1}\string|\MPx{#1}\string|\MPy{#1}\string|\MPw{#1}\string|\MPh{#1}\string|\MPd{#1}}}}

%D A few more low level macros take care of defining and
%D recalling actions. We could save this information in the
%D position containers themselves, this would save hash
%D entries, but at the cost of much more time consuming
%D expansion. Actions are saved globally!
%D
%D The lists can become quite long (also because there can
%D be lots of parameters passed on) so we provide a hook
%D to clean up the list afterwards.

\newtoks\everypositionaction
\newtoks\everyinsertpositionaction
\newtoks\everycleanpositionaction

\let\POSactionprefix\POSprefix

\unexpanded\def\dosetpositionaction#1%
  {\setgvalue{\POSactionprefix#1::}}

\def\doifpositionaction#1%
  {\ifcsname\POSactionprefix#1::\endcsname
     \expandafter\firstofoneargument
   \else
     \expandafter\gobbleoneargument
   \fi}

\def\doifpositionactionelse#1%
  {\ifcsname\POSactionprefix#1::\endcsname
     \expandafter\firstoftwoarguments
   \else
     \expandafter\secondoftwoarguments
   \fi}

\def\dopositionaction#1% test saves hash entry in etex
  {\ifcsname\POSactionprefix#1::\endcsname
     \positions_action_indeed{#1}%
   \fi}

\def\positions_action_indeed#1%
  {\ifcase\MPp{#1}\relax
     \traceposstring\clap\cyan{<#1>}% shouldn't happen too often
   \else
     \begingroup
     \setbox\scratchbox\hbox
       {\traceposstring\clap\red{<#1>}%
        \the\everyinsertpositionaction
        \the\everypositionaction
        \csname\POSactionprefix#1::\endcsname
        \positions_cleanup_action{#1}}%
     \smashedbox\scratchbox % smashing is really needed else we get problems with too big overlays
     \endgroup
   \fi}

%D Here the complication has to do with collecting actions
%D for later execution. This collection is especially handy
%D when we want to move actions to a specific layer.
%D Such series of actions are stored in a macro (the one
%D with the funny \type {++}) which is cleaned up after each
%D invocation.

% this can probably be done better

% \def\positions_cleanup_action#1% not in trialtypesetting
%   {\ifcsname\POSactionprefix#1++\endcsname
%      \the\everycleanpositionaction
%      \iflocalpositioning
%        \letgvalue{\POSactionprefix#1++}\empty
%      \else
%        \setxvalue{\POSactionprefix#1++}{\getvalue{\POSactionprefix#1++}}%
%      \fi
%    \fi}

\def\positions_cleanup_action#1% not in trialtypesetting
  {\ifcsname\POSactionprefix#1++\endcsname
     \the\everycleanpositionaction
     \iflocalpositioning
       % erase
       \expandafter\let\csname\POSactionprefix#1++\endcsname\empty
     \else
       % globalize
       \global\expandafter\let\csname\POSactionprefix#1++\expandafter\endcsname\csname\POSactionprefix#1++\endcsname
     \fi
   \fi}

\def\handlepositionaction#1\with#2\on#3% ugly
  {\begingroup
   \edef\!!stringa{\ifx\currentpositionoverlay\empty#3\else\currentpositionoverlay::\MPanchoridentifier\fi}%
   \edef\!!stringc{\POSactionprefix\!!stringa++}%
   \normalexpanded{\dosetpositionaction{\!!stringa}{\noexpand\getvalue{\!!stringc}}}%
   \global\let#1\relax
   \edef\!!stringb{\ifcsname\!!stringc\endcsname\csname\!!stringc\endcsname\fi}% why ...
   \setxvalue\!!stringc{\!!stringb#1#2}%
   \endgroup}

%D The next macros do some housekeeping.

\def\pageanchor{page:0} % for the moment only one pagesize
\def\textanchor{text:\the\realpageno}

%D The first version of this module implemented head and tail
%D anchors. Currently we stick to just one anchor and derive
%D the head and tail anchors from this one. We set these
%D anchors before and after each page.

% FOR THE MOMENT DISABLED (was downward compatibity issue)
%
% \def\headanchor{head:\the\realpageno} % virtual position
% \def\tailanchor{tail:\the\realpageno} % virtual position
%
% \def\presetpositionanchors % is this still needed?
%   {\ifpositioning
%      \positions_preset_anchors
%    \fi}
%
% \def\positions_preset_anchors
%   {\begingroup
%    \!!dimena\ifdim\topskip>\strutht\topskip\else\strutht\fi
%    \!!dimenb\dimexpr\MPy\textanchor+\MPh\textanchor-\!!dimena\relax
%    \!!dimenc\dimexpr\MPy\textanchor+\strutdp\relax
%    \!!dimend\MPx\textanchor
%    \!!dimene\MPw\textanchor
%    \replacepospxywhd\headanchor\realfolio\!!dimend\!!dimenb\!!dimene\!!dimena\strutdp
%    \replacepospxywhd\tailanchor\realfolio\!!dimend\!!dimenc\!!dimene\strutht \strutdp
%    \endgroup}
%
% \appendtoks \presetpositionanchors \to \beforeeverypage
% \appendtoks \presetpositionanchors \to \aftereverypage

% todo: change with each page size change .. can be made more efficient
% as some values are the same .. this one can (at some point) be used
% to provide correction for imposition

\unexpanded\def\positions_register_page#1% this one is flushed first ! ... can't we avoid this one
  {\ifpositioning\ifcase\realpageno\or
     \ifdim\printpaperheight=\paperheight
       \ifdim\printpaperwidth=\paperwidth
         % not needed,
       \else
         \positions_register_page_indeed{#1}%
       \fi
     \else
       \positions_register_page_indeed{#1}%
     \fi
   \fi\fi}

\def\positions_register_page_indeed#1%
  {\setbox#1\hbox{\hpos\pageanchor{\box#1}}}

\unexpanded\def\positions_place_anchors
  {\ifpositioning
     \positions_place_anchors_yes
   \else
     \positions_place_anchors_nop
   \fi}

% FOR THE MOMENT DISABLED
%
% \def\positions_place_anchors_yes % todo : depth pagebox
%   {\begingroup
%    \setbox\scratchbox\vbox to \textheight
%      {\simpletopskipcorrection
%       \hbox{\strut\dopositionaction\headanchor}%  ! actions on a virtual position
%       \vfill
%       \hbox{\strut\dopositionaction\tailanchor}}% ! actions on a virtual position
%    \dp\scratchbox\zeropoint
%    \wd\scratchbox\makeupwidth % not \zeropoint, else wrong text backgrounds
%    \hpos\textanchor{\box\scratchbox}%
%    \endgroup}

\def\positions_place_anchors_yes % todo : depth pagebox
  {\begingroup
   \setbox\scratchbox\emptyvbox
   \ht\scratchbox\textheight
   \dp\scratchbox\zeropoint
   \wd\scratchbox\makeupwidth
   \hpos\textanchor{\box\scratchbox}%
   \endgroup}

\def\positions_place_anchors_nop
  {\vskip\textheight}

%D \macros
%D   {positionoverlay,startpositionoverlay}
%D
%D As long as we're dealing with graphics it makes much sense
%D to use the available overlay mechanism. For this purpose, we
%D define some dedicated overlay extensions.
%D
%D \startbuffer[sample]
%D \defineoverlay [sample] [\positionoverlay{sample}]
%D
%D \startpositionoverlay{sample}
%D   \setMPpositiongraphic{A-1}{connectcenter}{from=A-1,to=A-2}
%D \stoppositionoverlay
%D \stopbuffer
%D
%D \typebuffer[sample]
%D
%D \startbuffer[graphic]
%D \startMPpositiongraphic{connectcenter}
%D   path pa, pb ; pair ca, cb ;
%D   initialize_box(\MPpos{\MPvar{from}}) ; pa := pxy ; ca := cxy ;
%D   initialize_box(\MPpos{\MPvar{to}}) ; pb := pxy ; cb := cxy ;
%D   draw pa withcolor red ;
%D   draw pb withcolor red ;
%D   draw ca -- cb withcolor blue ;
%D   anchor_box(\MPanchor{\MPvar{from}}) ;
%D \stopMPpositiongraphic
%D \stopbuffer
%D
%D We can best demonstrate this in an example, say:
%D
%D \startbuffer[text]
%D \framed
%D   [backgroundachtergrond=sample,align=middle,width=7cm]
%D   {We want to connect \hpos {A-1} {this} word with its
%D    grammatical cousin \hpos {A-2} {that}.}
%D \stopbuffer
%D
%D \typebuffer[text]
%D
%D \startlinecorrection
%D %\getbuffer[graphic,sample,text]
%D \stoplinecorrection
%D
%D The graphic is defined in the following way, using some
%D macros defined in an auxiliary \METAPOST\ module that is
%D preloaded.
%D
%D \typebuffer[graphic]

\def\MPanchoridentifier{mpa} % {mp-anchor}
\def\MPoverlayposprefix{MO::}

%D The rest of the definitions concerning such overlays may
%D look complicated,

\let\currentpositionoverlay\empty

%D Position actions are automatically executed when a position
%D is set.

\let\MPanchornumber\realfolio

\def\positionoverlay  % the test prevents too many redundant positions
  {\ifpositioning     % in (not used) text* position layers
     \expandafter\positions_overlay_indeed
   \else % also \iftrialtypesetting test here?
     \expandafter\gobbleoneargument
   \fi}

% keep this for a while
%
% \def\positions_overlay_indeed#1% the test prevents too many redundant positions
%   {\vbox to \overlayheight
%      {\doifpositionactionelse{#1::\MPanchoridentifier}%
%         {\edef\MPanchorid{#1::\MPanchoridentifier:\MPanchornumber}%
%          \edef\MPanchor##1{\MPpos{\MPanchorid}}%
%          \the\everyinsertpositionaction
%          \copyposition{#1::\MPanchoridentifier}{#1::\MPanchoridentifier:\MPanchornumber}%
%          \hpos
%            {#1::\MPanchoridentifier:\MPanchornumber}%
%           % this is ok
%           %{\hbox to \overlaywidth{\dopositionaction{#1::\MPanchoridentifier}\hss}}}%
%           % but this one prevents cyclic runs due to
%           % rounding errors
%            {\setbox\scratchbox\hbox to \overlaywidth{\dopositionaction{#1::\MPanchoridentifier}\hss}%
%             \ht\scratchbox\overlayheight
%             \dp\scratchbox\zeropoint
%             \box\scratchbox}}%
%         {\hbox to \overlaywidth{\hss}}%
%       \vfill}}

\def\positions_overlay_indeed#1%
  {\doifpositionactionelse{#1::\MPanchoridentifier}%
     \positions_overlay_yes\positions_overlay_nop{#1}}

\def\positions_overlay_yes#1%
  {\vbox to \overlayheight
     {\edef\MPanchorid{#1::\MPanchoridentifier:\MPanchornumber}%
      \edef\MPanchor##1{\MPpos\MPanchorid}%
      \the\everyinsertpositionaction
      \copyposition{#1::\MPanchoridentifier}\MPanchorid
      \hpos \MPanchorid
       %{\hbox to \overlaywidth{\dopositionaction{#1::\MPanchoridentifier}\hss}}}% oscillation due to rounding issues
        {\setbox\scratchbox\hbox to \overlaywidth{\dopositionaction{#1::\MPanchoridentifier}\hss}%
         \ht\scratchbox\overlayheight
         \dp\scratchbox\zeropoint
         \box\scratchbox}%
      \vfill}}

% \def\\positions_overlay_nop#1%
%   {\setbox\scratchbox\emptyvbox
%    \ht\scratchbox\overlayheight
%    \wd\scratchbox\overlaywidth
%    \box\scratchbox}

\let\positions_overlay_nop\gobbleoneargument

\unexpanded\def\startpositionoverlay
  {\iftrialtypesetting
     \expandafter\positions_overlay_start_nop
   \else
     \expandafter\positions_overlay_start_yes
   \fi}

\def\positions_overlay_start_nop#1\stoppositionoverlay
  {}

\def\positions_overlay_start_yes#1%
  {\def\currentpositionoverlay{#1}}

\unexpanded\def\stoppositionoverlay
  {\let\currentpositionoverlay\empty}

\def\resetpositionoverlay#1%
  {\dosetpositionaction{#1::\MPanchoridentifier::}{}}

\def\handlepositionboxes#1#2#3%
  {\handlepositionaction\dohandlepositionboxes\with{#1}{#2}{#3}\on{#2}}

\def\doinsertpositionboxes#1#2#3% pos tag setups
  {\ifnum\MPp{#1}=\realpageno\relax % can be sped up
     \executeifdefined{\MPoverlayposprefix#1}\gobblethreearguments{#1}{#2}{#3}%
   \fi}

\appendtoks
    \let\dohandlepositionboxes\doinsertpositionboxes % was handle ?
\to \everyinsertpositionaction

\def\docleanpositionboxes#1#2#3% pos tag setups
  {\ifnum\MPp{#1}<\realpageno \else
     \noexpand \dohandlepositionboxes{#1}{#2}{#3}% reinsert
   \fi}

\appendtoks
    \let\dohandlepositionboxes\docleanpositionboxes
\to \everycleanpositionaction

%D A position graphic is a normal (non||reused) \METAPOST\
%D graphic, used immediately, with zero dimensions, so that a
%D sequence of them does not harm.

\newbox\positiongraphicbox

\def\startMPpositiongraphic % id setups
  {\dodoublegroupempty\positions_mp_graphic_start}

\def\positions_mp_graphic_start#1#2#3\stopMPpositiongraphic % tag list mpcode
  {\setgvalue{MPG:#1}{\positions_mp_graphic_use{#1}{#2}{#3}}}

\let\stopMPpositiongraphic\relax

\def\positions_mp_graphic_prepare
  {\ifcsname\@@meta self\endcsname\else\letvalue{\@@meta self}\currentposition\fi
   \ifcsname\@@meta from\endcsname\else\letvalue{\@@meta from}\currentposition\fi}

\def\positions_mp_graphic_use#1#2#3%
  {\begingroup
   \prepareMPvariables{#2}%
   \positions_mp_graphic_prepare
   \enableincludeMPgraphics
   \startMPcode#3\stopMPcode
   \endgroup}

\def\MPpositiongraphic
  {\dodoublegroupempty\positions_mp_graphic_direct}

% \def\positions_mp_graphic_direct#1#2% tag setups
%   {\begingroup
%    \def\@@meta{#1:}%
%    \setupMPvariables[#2]%
%    \positions_mp_graphic_prepare
%    \MPshiftdrawingtrue
%    \def\positions_mp_graphic_direct{\positions_mp_graphic_nested{#2}}% takes two extra arguments
%    \setbox\positiongraphicbox\hbox
%      {\ignorespaces
%       \ifcsname MPM:#1\endcsname \csname MPM:#1\endcsname \else
%       \ifcsname MPG:#1\endcsname \csname MPG:#1\endcsname \fi\fi
%       \removelastspace}%
%    \smashbox\positiongraphicbox
%    \box\positiongraphicbox
%    \endgroup}

\def\positions_mp_graphic_direct#1% tag setups
  {\ifcsname MPM:#1\endcsname
     \expandafter\positions_mp_graphic_direct_indeed_mpm
   \else\ifcsname MPG:#1\endcsname
     \doubleexpandafter\positions_mp_graphic_direct_indeed_mpg
   \else
     \doubleexpandafter\positions_mp_graphic_direct_indeed_nop
   \fi\fi{#1}}

\let\positions_mp_graphic_direct_indeed_nop\gobbletwoarguments

\def\positions_mp_graphic_direct_indeed_mpm
  {\positions_mp_graphic_direct_indeed{MPM}}

\def\positions_mp_graphic_direct_indeed_mpg
  {\positions_mp_graphic_direct_indeed{MPG}}

\def\positions_mp_graphic_direct_indeed#1#2#3% what tag setups
  {\begingroup
   \def\@@meta{#2:}% will become a commandhandler
   \setupMPvariables[#3]%
   \positions_mp_graphic_prepare
   \MPshiftdrawingtrue
   \def\positions_mp_graphic_direct{\positions_mp_graphic_nested{#3}}% takes two extra arguments
   \setbox\positiongraphicbox\hbox
     {\ignorespaces\csname#1:#2\endcsname\removelastspace}%
   \smashbox\positiongraphicbox
   \box\positiongraphicbox
   \endgroup}

\def\positions_mp_graphic_nested#1#2#3% nesting used in prikkels / pascal
  {\begingroup
   \def\@@meta{#2:}%
   \setupMPvariables[#1,#3]%
   \positions_mp_graphic_prepare
   \getvalue{MPG:#2}%
   \endgroup}%

\long\def\startMPpositionmethod#1#2\stopMPpositionmethod
  {\long\setgvalue{MPM:#1}{#2}} % todo: var list here

\let\stopMPpositionmethod\relax

%D Simple one position graphics.

\def\setMPpositiongraphic
  {\dotriplegroupempty\dosetMPpositiongraphic}

\def\dosetMPpositiongraphic#1#2#3% pos tag vars
  {\ifx\currentpositionoverlay\empty
     \dosetpositionaction{#1}{\MPpositiongraphic{#2}{#3}}%
   \else % silly can be one
     \handlepositiongraphics{#1}{#2}{#3}%
   \fi}

\def\handlepositiongraphics#1#2#3% combine with boxes
  {\handlepositionaction\dohandleMPpositiongraphic\with{#1}{#2}{#3}\on{#2}}

\def\doinsertMPpositiongraphic#1#2#3% pos tag setups
  {\ifnum\MPp{#1}=\realpageno\relax % extra saveguard
     \def\currentposition{#1}\MPpositiongraphic{#2}{#3}%
   \fi}

\appendtoks
    \let\dohandleMPpositiongraphic\doinsertMPpositiongraphic
\to \everyinsertpositionaction

\def\docleanMPpositiongraphic#1#2#3% pos tag setups
  {\ifnum\MPp{#1}<\realpageno \else
     \noexpand\dohandleMPpositiongraphic{#1}{#2}{#3}%
   \fi}

\appendtoks
    \let\dohandleMPpositiongraphic\docleanMPpositiongraphic
\to \everycleanpositionaction

%D Graphics that span two positions (beware, does not cross pages).

\unexpanded\def\setMPpositiongraphicrange
  {\doquadruplegroupempty\dosetMPpositiongraphicrange}

\def\dosetMPpositiongraphicrange#1#2#3#4% bpos epos tag vars
  {\ifx\currentpositionoverlay\empty
     \dosetpositionaction{#1}{\MPpositiongraphic{#3}{#4}}%
   \else
     \handlepositiongraphicsrange{#1}{#2}{#3}{#4}%
   \fi}

\def\handlepositiongraphicsrange#1#2#3#4%
  {\handlepositionaction\dohandleMPpositiongraphicrange\with{#1}{#2}{#3}{#4}\on{#2}}

\def\doinsertMPpositiongraphicrange#1#2#3#4% pos pos tag setups
  {\ifnum\MPp{#1}\MPp{#2}>\zerocount
     \iflocalpositioning
       \donetrue
     \else
       \donefalse
       \ifnum\MPp{#1}=\realpageno
         \donetrue
       \else\ifnum\MPp{#2}=\realpageno
         \donetrue
       \else\ifnum\MPp{#1}<\realpageno\relax\ifnum\MPp{#2}>\realpageno
         \donetrue
       \fi\fi\fi\fi
     \fi
     \ifdone
       \def\currentposition{#1}\MPpositiongraphic{#3}{#4}%
     \fi
   \fi}

\appendtoks
    \let\dohandleMPpositiongraphicrange\doinsertMPpositiongraphicrange
\to \everyinsertpositionaction

\def\docleanMPpositiongraphicrange#1#2#3#4% pos tag setups
  {\ifnum\MPp{#2}<\realpageno \else
     \noexpand \dohandleMPpositiongraphicrange{#1}{#2}{#3}{#4}%
   \fi}

\appendtoks
    \let\dohandleMPpositiongraphicrange\docleanMPpositiongraphicrange
\to \everycleanpositionaction

%D \macros
%D   {stackposdown, stackposup, stackposleft,stackposright}
%D
%D This is sort of obsolete as we have now stacking in the
%D margin in a different way.

\def\stackposdistance{.5em}

\newcount\currentautopos
\newcount\previousautopos

\def\POSstackprefix{stack:}

\unexpanded\def\dostackposbox#1#2%
  {\dowithnextbox
     {#2%
      \bgroup
      \previousautopos\currentautopos
      \global\advance\currentautopos\plusone
      \edef\currentposition {\POSstackprefix\number\currentautopos}%
      \edef\previousposition{\POSstackprefix\number\previousautopos}%
      \hpos\currentposition{\doifoverlappingelse\currentposition\previousposition{#1}{\flushnextbox}%
      \egroup}}%
     \hbox}

\unexpanded\def\stackposup   {\dostackposbox{\raise\lineheight\flushnextbox}}
\unexpanded\def\stackposdown {\dostackposbox{\lower\lineheight\flushnextbox}}
\unexpanded\def\stackposleft {\dostackposbox{\copy\nextbox\hskip\nextboxwd\hskip\stackposdistance}}
\unexpanded\def\stackposright{\dostackposbox{\hskip\stackposdistance\hskip\nextboxwd\flushnextbox}}

\protect \endinput