%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 the reference point
%D on the page. The next macros do so and are hooked into the page building routine.

\registerctxluafile{anch-pgr}{}

\unprotect

%D A few more low level macros take care of defining and recalling actions. Actions
%D are saved globally! The lists can become quite long because there can be lots of
%D parameters passed on so we clean up the list afterwards.

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

\installcorenamespace{positionaction}
\installcorenamespace{positioncleanup}

\unexpanded\def\anch_positions_set_action#1%
  {\expandafter\gdef\csname\??positionaction#1\endcsname} % nicely gobbles spaces

\unexpanded\def\doifpositionaction#1%
  {\ifcsname\??positionaction#1\endcsname
     \expandafter\firstofoneargument
   \else
     \expandafter\gobbleoneargument
   \fi}

\unexpanded\def\doifelsepositionaction#1%
  {\ifcsname\??positionaction#1\endcsname
     \expandafter\firstoftwoarguments
   \else
     \expandafter\secondoftwoarguments
   \fi}

\let\doifpositionactionelse\doifelsepositionaction

\unexpanded\def\dopositionaction#1%
  {\edef\currentpositionaction{#1}%
   \ifcsname\??positionaction\currentpositionaction\endcsname
     \anch_positions_action_indeed
   \fi}

\def\anch_positions_action_indeed
  {\doifelseposition\currentpositionaction
     \anch_positions_action_indeed_yes
     \anch_positions_action_indeed_nop}

\def\anch_positions_action_indeed_nop
  {\anch_positions_trace_action_nop}

\def\anch_positions_action_indeed_yes % we need a way to figure out if we have actions
  {\begingroup
   \setbox\scratchbox\hbox % \hpack
     {\anch_positions_trace_action_yes
      \the\everyinsertpositionaction
      \the\everypositionaction
      \begincsname\??positionaction\currentpositionaction\endcsname
      \anch_positions_cleanup_action}%
   \smashedbox\scratchbox % smashing is really needed else we get problems with too big overlays
   \endgroup}

\unexpanded\def\anch_positions_trace_action_nop_indeed
  {\anch_positions_trace\clap\darkred{<\currentpositionaction>}}

\unexpanded\def\anch_positions_trace_action_yes_indeed
  {\anch_positions_trace\clap\darkgreen{<\currentpositionaction>}}

\let\anch_positions_trace_action_nop\relax
\let\anch_positions_trace_action_yes\relax

\appendtoks
    \let\anch_positions_trace_action_nop\anch_positions_trace_action_nop_indeed
    \let\anch_positions_trace_action_yes\anch_positions_trace_action_yes_indeed
\to \t_anch_positions_tracers

%D Here the complication has to do with collecting actions for later execution. This
%D collection is especially handy when we want to move actions to a specific layer.
%D Such series of actions are stored in a macro that is cleaned up after each
%D invocation.

\def\anch_positions_cleanup_action % not in trialtypesetting
  {\ifcsname\??positioncleanup\currentpositionaction\endcsname
     \the\everycleanpositionaction
     \setxvalue{\??positioncleanup\currentpositionaction}{\csname\??positioncleanup\currentpositionaction\endcsname}%
   \fi}

\def\handlepositionaction#1\with#2\on#3% ugly
  {\begingroup
   \edef\currentpositionanchor
     {\ifx\currentpositionoverlay\empty#3\else\currentpositionoverlay::\MPanchoridentifier\fi}%
   \normalexpanded{\anch_positions_set_action{\currentpositionanchor}{\noexpand\getvalue{\??positioncleanup\currentpositionanchor}}}%
   \let#1\relax
   \ifcsname\??positioncleanup\currentpositionanchor\endcsname
     \setxvalue{\??positioncleanup\currentpositionanchor}%
       {\csname\??positioncleanup\currentpositionanchor\endcsname#1#2}%
   \else
     \setxvalue{\??positioncleanup\currentpositionanchor}%
       {#1#2}%
   \fi
   \endgroup}

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

\newdimen\c_anch_page_width
\newdimen\c_anch_page_height

\unexpanded\def\anch_positions_register_page#1% this one is flushed first ! ... can't we avoid this one
  {\ifpositioning\ifcase\realpageno\or
     \ifdim\c_anch_page_height=\paperheight
       \ifdim\c_anch_page_width=\paperwidth
         % no change
       \else
         \c_anch_page_width \paperwidth
         \c_anch_page_height\paperheight
         \anch_make_page_box{#1}% \ifvbox#1\setbox#1\hpack{\box#1}\fi
       \fi
     \else
       \c_anch_page_width \paperwidth
       \c_anch_page_height\paperheight
       \anch_make_page_box{#1}% \ifvbox#1\setbox#1\hpack{\box#1}\fi
     \fi
   \fi\fi}

\unexpanded\def\anch_positions_place_anchors
  {\ifpositioning
     \anch_positions_place_anchors_yes
   \else
     \anch_positions_place_anchors_nop
   \fi}

\def\anch_positions_place_anchors_yes % todo : depth pagebox
  {\begingroup
   \setbox\scratchbox\emptyhbox
   \ht\scratchbox\textheight
   \dp\scratchbox\zeropoint % redundant
   \wd\scratchbox\makeupwidth
   \anch_mark_text_box\scratchbox
   \box\scratchbox
   \endgroup}

\def\anch_positions_place_anchors_nop
  {\vkern\textheight}

%D \macros
%D   {positionoverlay,startpositionoverlay}
%D
%D As long as we're dealing with graphics it makes much sense to use the available
%D overlay mechanism. For this purpose, we 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 macros defined in an
%D auxiliary \METAPOST\ module that is preloaded.
%D
%D \typebuffer[graphic]

\def\MPanchoridentifier{mpa}  % {mp-anchor}

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

\let\currentpositionoverlay\empty

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

\def\textbackgroundoverlay#1{\v!text#1}
\def\MPanchornumber         {\the\realpageno}

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

\def\anch_positions_overlay_indeed#1%
  {\begingroup
   \edef\currentpositionoverlay{#1}%
   \ifcsname\??positionaction\currentpositionoverlay::\MPanchoridentifier\endcsname
     \anch_positions_overlay_compose
   \fi
   \endgroup}

\def\MPoverlayanchor#1{\MPpos\MPanchorid}

\def\anch_positions_overlay_compose
  {\vpack to \d_overlay_height
     {%\writestatus{!!!}{\currentpositionoverlay/\MPanchoridentifier/\MPanchornumber}%
      \edef\MPanchorid{\currentpositionoverlay::\MPanchoridentifier:\MPanchornumber}% realpageno
    % \edef\MPanchor##1{\MPpos\MPanchorid}%
      \let\MPanchor\MPoverlayanchor % no need to fetch it already, seldom used
      \the\everyinsertpositionaction
      \copyposition{\currentpositionoverlay::\MPanchoridentifier}\MPanchorid
      \setbox\scratchbox\hbox to \d_overlay_width % \hpack
        {\dopositionaction{\currentpositionoverlay::\MPanchoridentifier}\hss}%
      \ht\scratchbox\d_overlay_height
      \dp\scratchbox\zeropoint
      \anch_mark_tagged_box\scratchbox\MPanchorid % needs an hbox
      \box\scratchbox
      \vfill}}

\unexpanded\def\positionregionoverlay  % shares regions
  {\ifpositioning
     \expandafter\anch_positions_region_overlay_indeed
   \else % also \iftrialtypesetting test here?
     \expandafter\gobbletwoarguments
   \fi}

\let\currentpositionregion\empty

\def\anch_positions_region_overlay_indeed#1#2%
  {\begingroup
   \edef\currentpositionregion {#1}%
   \edef\currentpositionoverlay{#2}%
   \ifcsname\??positionaction\currentpositionoverlay::\MPanchoridentifier\endcsname
     \anch_positions_region_overlay_compose
   \fi
   \endgroup}

\def\anch_positions_region_overlay_compose
  {\vpack to \d_overlay_height
     {\let\MPanchorid\currentpositionregion
      \let\MPanchor\MPoverlayanchor % no need to fetch it already, seldom used
      \the\everyinsertpositionaction
      \copyposition{\currentpositionoverlay::\MPanchoridentifier}\MPanchorid
      \setbox\scratchbox\hbox to \d_overlay_width % \hpack
        {\dopositionaction{\currentpositionoverlay::\MPanchoridentifier}\hss}%
      \ht\scratchbox\d_overlay_height
      \dp\scratchbox\zeropoint
      \box\scratchbox
      \vfill}}

% \let\anch_positions_overlay_nop\gobbleoneargument

\unexpanded\def\startpositionoverlay
  {\iftrialtypesetting
     \expandafter\anch_positions_overlay_start_nop
   \else
     \expandafter\anch_positions_overlay_start_yes
   \fi}

\let\stoppositionoverlay\relax

\def\anch_positions_overlay_start_nop#1\stoppositionoverlay
  {}

\ifdefined\checkpositionoverlays \else \let\checkpositionoverlays\relax \fi

\let\currentpositionoverlay\empty

\def\anch_positions_overlay_start_yes#1%
  {\checkpositionoverlays
   \edef\currentpositionoverlay{#1}}

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

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

\installcorenamespace{positiongraphic}
\installcorenamespace{positionmethod}
%installcorenamespace{graphicvariable}

\newbox\b_anch_positions_graphic

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

\def\anch_positions_meta_graphic_start#1#2#3\stopMPpositiongraphic % tag list mpcode
  {\setgvalue{\??positiongraphic#1}{\anch_positions_meta_graphic_use{#1}{#2}{#3}}}

\let\stopMPpositiongraphic\relax

\def\anch_positions_meta_graphic_prepare
  {\ifcsname\??graphicvariable\currentmpvariableclass:self\endcsname \else
     \letvalue{\??graphicvariable\currentmpvariableclass:self}\currentposition
   \fi
   \ifcsname\??graphicvariable\currentmpvariableclass:from\endcsname \else
     \letvalue{\??graphicvariable\currentmpvariableclass:from}\currentposition
   \fi}

\def\anch_positions_meta_graphic_use#1#2#3%
  {\begingroup
   \meta_prepare_variables{#2}%
   \anch_positions_meta_graphic_prepare
   \startMPcode#3\stopMPcode
   \endgroup}

\unexpanded\def\MPpositiongraphic
  {\dodoublegroupempty\anch_positions_meta_graphic_direct}

\def\anch_positions_meta_graphic_direct#1% tag setups
  {\ifcsname\??positionmethod#1\endcsname % method
     \expandafter\anch_positions_meta_graphic_direct_indeed_method
   \else\ifcsname\??positiongraphic#1\endcsname
     \doubleexpandafter\anch_positions_meta_graphic_direct_indeed_normal
   \else
     \doubleexpandafter\anch_positions_meta_graphic_direct_indeed_unknown
   \fi\fi{#1}}

\let\anch_positions_meta_graphic_direct_indeed_unknown\gobbletwoarguments

\def\anch_positions_meta_graphic_direct_indeed_method
  {\anch_positions_meta_graphic_direct_indeed\??positionmethod}

\def\anch_positions_meta_graphic_direct_indeed_normal
  {\anch_positions_meta_graphic_direct_indeed\??positiongraphic}

\def\anch_positions_meta_graphic_direct_indeed#1#2#3% what tag setups
  {\begingroup
   \setupMPvariables[#2][#3]%
   \edef\currentmpvariableclass{#2}%
   \anch_positions_meta_graphic_prepare
   \obeyMPboxorigin % do we also set the size ? when needed this must be done in mp ... might change
   \def\anch_positions_meta_graphic_direct{\anch_positions_meta_graphic_nested{#3}}% takes two extra arguments
   \setbox\b_anch_positions_graphic\hbox % \hpack
     {\ignorespaces\begincsname#1#2\endcsname\removelastspace}%
   \smashbox\b_anch_positions_graphic
   \box\b_anch_positions_graphic
   \endgroup}

\def\anch_positions_meta_graphic_nested#1#2#3% nesting used in prikkels / pascal (might go away)
  {\begingroup
   \setupMPvariables[#2][#1,#3]%
   \edef\currentmpvariableclass{#2}%
   \anch_positions_meta_graphic_prepare
   \begincsname\??positiongraphic#2\endcsname
   \endgroup}%

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

\let\stopMPpositionmethod\relax

%D Simple one position graphics.

\unexpanded\def\setMPpositiongraphic
  {\dotriplegroupempty\anch_positions_meta_graphic_set}

\def\anch_positions_meta_graphic_set#1#2#3% pos tag vars
  {\ifx\currentpositionoverlay\empty
     \anch_positions_set_action{#1}{\MPpositiongraphic{#2}{#3}}%
   \else % silly can be one
     \anch_positions_meta_graphic_handle{#1}{#2}{#3}%
   \fi}

\def\anch_positions_meta_graphic_handle#1#2#3% combine with boxes
  {\handlepositionaction\anch_positions_meta_graphic_handle_indeed\with{#1}{#2}{#3}\on{#2}}

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

\let\anch_positions_meta_graphic_handle_indeed\relax

\appendtoks
    \let\anch_positions_meta_graphic_handle_indeed\anch_positions_meta_graphic_insert
\to \everyinsertpositionaction

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

\appendtoks
    \let\anch_positions_meta_graphic_handle_indeed\anch_positions_meta_graphic_cleanup
\to \everycleanpositionaction

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

\unexpanded\def\setMPpositiongraphicrange
  {\doquadruplegroupempty\anch_positions_meta_graphic_set_range}

\def\anch_positions_meta_graphic_set_range#1#2#3#4% bpos epos tag vars
  {\ifx\currentpositionoverlay\empty
     \anch_positions_set_action{#1}{\MPpositiongraphic{#3}{#4}}%
   \else
     \anch_positions_meta_graphic_handle_range{#1}{#2}{#3}{#4}%
   \fi}

\def\anch_positions_meta_graphic_handle_range#1#2#3#4%
  {\handlepositionaction\anch_positions_meta_graphic_handle_range_indeed\with{#1}{#2}{#3}{#4}\on{#2}}

\def\anch_positions_meta_graphic_insert_range#1#2#3#4% pos pos tag setups
  {\clf_doifelserangeonpage{#1}{#2}\realpageno
     {\def\currentposition{#1}%
      \MPpositiongraphic{#3}{#4}}%
     {}}

\appendtoks
    \let\anch_positions_meta_graphic_handle_range_indeed\anch_positions_meta_graphic_insert_range
\to \everyinsertpositionaction

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

\appendtoks
    \let\anch_positions_meta_graphic_handle_range_indeed\anch_positions_meta_graphic_cleanup_range
\to \everycleanpositionaction

\let\anch_positions_meta_graphic_handle_range_indeed\gobblefourarguments

% Helpers:

\def\MPgetposboxes #1#2{\clf_fetchposboxes{#1}{#2}\realpageno}
\def\MPgetmultipars#1#2{\clf_fetchmultipar{#1}{#2}\realpageno}

\protect \endinput