%D \module
%D   [       file=anch-bar,
%D        version=2003.03.16,
%D          title=\CONTEXT\ Anchoring Macros,
%D       subtitle=Margin Bars and alike,
%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 / Margin Bars}

\unprotect

%D We will implement a sidebar mechanism using the
%D functionality from \type {core-pos}.
%D
%D \starttyping
%D \definesidebar[whow][rulecolor=green,distance=]
%D
%D \input tufte \par
%D \startsidebar
%D   \input tufte \par
%D   \input tufte \par
%D   \startsidebar[whow]
%D     \input tufte \par
%D     \input tufte \par
%D     \input tufte
%D   \stopsidebar \par
%D   \input tufte \par
%D   \input tufte
%D \stopsidebar \par
%D \input tufte \par
%D \input tufte \par
%D \startsidebar
%D   \input tufte \par
%D   \input tufte \par
%D   \input tufte \par
%D   \input tufte \par
%D   \input tufte
%D \stopsidebar \par
%D \input tufte \par
%D \input tufte \par
%D \startsidebar
%D   \input tufte
%D   \input tufte
%D   \input tufte
%D   \input tufte
%D   \input tufte
%D \stopsidebar
%D \stoptyping

\newcount\currentsidebar
\newdimen\sidebardistance

\def\setupsidebars
  {\dodoubleargument\dosetupsidebars}

\def\dosetupsidebars[#1][#2]%
  {\ifsecondargument
     \getparameters[\??br#1][#2]%
   \else
     \getparameters[\??br][#1]%
   \fi}

% \setupMPvariables
%   [mpos:bar]
%   [linecolor=red,
%    linewidth=2pt,
%    distance=5pt]

\setupsidebars
  [\c!rulethickness=2pt,
   \c!rulecolor=red,
   \c!distance=.5\bodyfontsize]

\def\definesidebar
  {\dodoubleempty\dodefinesidebar}

\def\dodefinesidebar[#1][#2]%
  {\copyparameters
     [\??br#1][\??br]
     [\c!rulethickness,\c!rulecolor,\c!distance]%
   \getparameters
     [\??br#1][#2]}

\def\startsidebar
  {\dosingleempty\dostartsidebar}

\def\dostartsidebar[#1]%
  {\bgroup
   \dontleavehmode
   \checktextbackgrounds
   \global\advance\currentsidebar\plusone
   \doifelsenothing{#1}
     {\advance\sidebardistance\@@brdistance}
     {\doifelsevaluenothing{\??br#1\c!distance}
        {\advance\sidebardistance\@@brdistance}
        {\sidebardistance\getvalue{\??br#1\c!distance}}}%
   \startpositionoverlay{text-1}%
     \expanded{\setMPpositiongraphicrange
       {b:side:\the\currentsidebar}%
       {e:side:\the\currentsidebar}%
       {mpos:bar}%
       {self=side:\the\currentsidebar,
        linewidth=\getvalue{\??br#1\c!rulethickness},
        linecolor=\getvalue{\??br#1\c!rulecolor},
        distance=\the\sidebardistance}}%
   \stoppositionoverlay
   \bpos{side:\the\currentsidebar}\ignorespaces}

% \def\dostopsidebar#1%
%   {\removelastspace\tpos{side:#1}\carryoverpar\egroup}

\def\stopsidebar
  {\removelastspace\tpos{side:\the\currentsidebar}\carryoverpar\egroup}

\startMPpositionmethod{mpos:bar}
  \startMPpositiongraphic{mpos:bar}{linecolor,linewidth,distance}%
    StartPage ;
      path p ; p :=
      if \MPp\MPbself=\MPp\MPeself :
        (xpart ulcorner Field[Text][Text],\MPy\MPbself+\MPh\MPbself) --
        (xpart llcorner Field[Text][Text],\MPy\MPeself-\MPd\MPeself) ;
      elseif RealPageNumber=\MPp\MPbself :
        (xpart ulcorner Field[Text][Text],\MPy\MPbself+\MPh\MPbself) --
        (llcorner Field[Text][Text]) ;
      elseif RealPageNumber=\MPp\MPeself :
        (ulcorner Field[Text][Text]) --
        (xpart llcorner Field[Text][Text],\MPy\MPeself-\MPd\MPeself) ;
      else :
        (ulcorner Field[Text][Text]) --
        (llcorner Field[Text][Text]) ;
      fi ;
      p := p shifted (-llcorner Field[Text][Text]-(\MPvar{distance},0)) ;
      interim linecap := butt ;
      draw p
        withpen pencircle scaled \MPvar{linewidth}
        withcolor \MPvar{linecolor} ;
    StopPage ;
  \stopMPpositiongraphic
  \MPpositiongraphic{mpos:bar}{}%
\stopMPpositionmethod

%D We now reimplement the margin rules handler defined in
%D \type {core-rul}:
%D
%D \setupmarginrules[level=5]
%D
%D \startmarginrule[1]
%D First we set the level at~5. Next we typeset this first
%D paragraph as a level~1 one. As expected no rule show up.
%D \stopmarginrule
%D
%D \startmarginrule[5]
%D The second paragraph is a level~5 one. As we can see here,
%D the marginal rule gets a width according to its level.
%D \stopmarginrule
%D
%D \startmarginrule[8]
%D It will of course be no surprise that this third paragraph
%D has a even thicker margin rule. This behavior can be
%D overruled by specifying the width explictly.
%D \stopmarginrule

\definesidebar
  [\v!margin]
  [\c!rulecolor=\s!black,
   \c!rulethickness=\@@karulethickness,
   \c!distance=\dimexpr\leftmargindistance-\@@karulethickness/2\relax]

\definecomplexorsimple\startmarginrule

\def\simplestartmarginrule
  {\complexstartmarginrule[1]}

\def\complexstartmarginrule[#1]%
  {\bgroup
   \ifnum#1<\@@kalevel\relax
     \let\stopmarginrule\egroup
   \else
     \def\@@kadefaultwidth{#1}%
     \let\stopmarginrule\dostopmarginrule
     \@EA\startsidebar\@EA[\@EA\v!margin\@EA]%
   \fi}

\def\dostopmarginrule
  {\stopsidebar
   \egroup}

\protect \endinput