%D \module
%D   [       file=core-vis,
%D        version=1996.06.01,
%D          title=\CONTEXT\ Core Macros,
%D       subtitle=Visualization,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA / Hans Hagen \& Ton Otten}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. Non||commercial use is 
%C granted. 

%D This module adds some more visualization cues to the ones 
%D supplied in the support module. 
%D 
%D %\everypar   dual character, \the\everypar and \everypar=
%D %\hrule      cannot be grabbed in advance, switches mode
%D %\vrule      cannot be grabbed in advance, switches mode
%D %
%D %\indent     only explicit ones
%D %\noindent   only explicit ones
%D %\par        only explicit ones
%D
%D %\leftskip   only if explicit one
%D %\rightskip  only if explicit one

\writestatus{loading}{Context Support Macros / Visualization}

\unprotect

%D \macros
%D   {indent, noindent,
%D    leavevmode,
%D    par}
%D   {}
%D 
%D \TeX\ acts upon paragraphs. In mosts documents paragraphs 
%D are separated by empty lines, which internally are handled as
%D \type{\par}. Paragraphs can be indented or not, depending on
%D the setting of \type{\parindent}, the first token of a 
%D paragraph and/or user suppressed or forced indentation. 
%D 
%D Because the actual typesetting is based on both explicit
%D user and implicit system actions, visualization is only
%D possible for the user supplied \type{\indent},
%D \type{\noindent}, \type{\leavevmode} and \type{\par}. Other
%D 'clever' tricks will quite certainly lead to more failures
%D than successes, so we only support these three explicit 
%D primitives and one macro: 

\let\normalnoindent   = \noindent
\let\normalindent     = \indent
\let\normalpar        = \par

\let\normalleavevmode = \leavevmode

\def\showparagraphcue#1#2#3#4#5%
  {\bgroup
   \scratchdimen#1\relax
   \dontinterfere
   \dontcomplain
   \boxrulewidth=5\testrulewidth 
   #3#4\relax
   \setbox0=\normalhbox to \scratchdimen
     {#2{\ruledhbox to \scratchdimen
           {\vrule 
              #5 20\testrulewidth 
              \!!width \!!zeropoint
            \normalhss}}}%
   \smashbox0
   \normalpenalty\!!tenthousand
   \box0
   \egroup}

\def\ruledhanging%
  {\ifdim\hangindent>\!!zeropoint\relax
     \ifnum\hangafter<0
       \normalhbox 
         {\boxrulewidth=5\testrulewidth
          \setbox0=\ruledhbox to \hangindent
            {\scratchdimen=\ht\strutbox
             \advance\scratchdimen by \dp\strutbox
             \vrule
               \!!width\!!zeropoint
               \!!height\!!zeropoint
               \!!depth-\hangafter\scratchdimen}%
          \normalhskip-\hangindent
          \smashbox0
          \raise\ht\strutbox\box0}%
     \fi
   \fi}

\def\ruledparagraphcues%
  {\bgroup
   \dontcomplain
   \normalhbox to \!!zeropoint
     {\ifdim\leftskip>\!!zeropoint\relax
        \showparagraphcue\leftskip\llap\relax\relax\!!depth
        \normalhskip-\leftskip
      \fi
      \ruledhanging
      \normalhskip\hsize
      \ifdim\rightskip>\!!zeropoint\relax
        \normalhskip-\rightskip
        \showparagraphcue\rightskip\relax\relax\relax\!!depth
      \fi}%
   \egroup}

\def\ruledpar%
  {\relax
   \ifhmode 
     \showparagraphcue{40\testrulewidth}\relax\rightrulefalse\relax\!!height 
   \fi
   \normalpar}

\def\rulednoindent%  
  {\relax
   \normalnoindent
   \ruledparagraphcues
   \showparagraphcue{40\testrulewidth}\llap\leftrulefalse\relax\!!height}

\def\ruledindent%  
  {\relax 
   \normalnoindent 
   \ruledparagraphcues
   \ifdim\parindent>\!!zeropoint\relax
     \showparagraphcue\parindent\relax\relax\relax\!!height 
   \else
     \showparagraphcue{40\testrulewidth}\llap\relax\relax\!!height 
   \fi
   \normalhskip\parindent}

\def\ruledleavevmode%
  {\relax
   \normalleavevmode
   \ifdim\parindent>\!!zeropoint\relax
     \normalhskip-\parindent
     \ruledparagraphcues
     \showparagraphcue\parindent\relax\leftrulefalse\rightrulefalse\!!height 
     \normalhskip\parindent
   \else
     \ruledparagraphcues
     \showparagraphcue{40\testrulewidth}\llap\leftrulefalse\rightrulefalse\!!height 
   \fi}

\def\dontshowimplicits%
  {\let\noindent   = \normalnoindent  
   \let\indent     = \normalindent    
   \let\leavevmode = \normalleavevmode
   \let\par        = \normalpar}

\def\showimplicits%
  {\testrulewidth  = \defaulttestrulewidth
   \let\noindent   = \rulednoindent  
   \let\indent     = \ruledindent    
   \let\leavevmode = \ruledleavevmode
   \let\par        = \ruledpar}

%D The next few||line examples show the four cues. Keep in 
%D mind that we only see them when we explicitly open or close
%D a paragraph. 
%D 
%D \bgroup
%D \def\voorbeeld#1%
%D   {#1Visualizing some \TeX\ primitives and Plain \TeX\
%D    macros can be very instructive, at least it is to me.
%D    Here we see {\tt\string#1} and {\tt\string\ruledpar} in
%D    action, while {\tt\string\parindent} equals
%D    {\tt\the\parindent}.\ruledpar} 
%D 
%D \showimplicits
%D 
%D \voorbeeld \indent   
%D \voorbeeld \noindent   
%D \voorbeeld \leavevmode 
%D 
%D \parindent=60pt
%D 
%D \voorbeeld \indent     
%D \voorbeeld \noindent   
%D \voorbeeld \leavevmode 
%D
%D \startsmaller
%D \voorbeeld \indent     
%D \voorbeeld \noindent   
%D \voorbeeld \leavevmode 
%D \stopsmaller
%D \egroup
%D
%D These examples also demonstrate the visualization of 
%D \type{\leftskip} and \type{\rightskip}. 

\newcounter\ruledbaselines

\def\debuggertext#1%
  {\ifx\ttxx\undefined
     $\scriptscriptstyle#1$%
   \else
     {\ttxx#1}%
   \fi}

\def\ruledbaseline%
  {\vrule \!!width \!!zeropoint
   \bgroup
   \dontinterfere
   \doglobal\increment\ruledbaselines
   \scratchdimen=3\baselineskip
   \setbox\scratchbox=\normalvbox to 2\scratchdimen
     {\leaders
        \normalhbox
          {\strut
           \vrule
             \!!height \testrulewidth
             \!!depth \testrulewidth
             \!!width 120pt}
      \normalvfill}%
   \smashbox\scratchbox
   \advance\scratchdimen by \strutheightfactor\baselineskip
   \setbox\scratchbox=\normalhbox
     {\normalhskip -48pt
      \normalhbox to 24pt
        {\normalhss\debuggertext\ruledbaselines\normalhskip6pt}%
      \raise\scratchdimen\box\scratchbox}%
   \smashbox\scratchbox
   \box\scratchbox
   \egroup}

\def\showbaselines%
  {\testrulewidth=\defaulttestrulewidth
   \EveryPar{\ruledbaseline}}

%D {\em Not yet documented!}

\def\makecutbox#1%
  {\edef\ruledheight{\the\ht#1}%
   \edef\ruleddepth {\the\dp#1}%
   \edef\ruledwidth {\the\wd#1}%
   \setbox\scratchbox=\normalvbox
     {\dontcomplain
      \offinterlineskip
      \scratchdimen=12pt\relax
      \def\verrule##1##2%
        {\vrule
           \!!width\boxrulewidth
           \!!height##1\scratchdimen
           \!!depth##2\scratchdimen}%
      \def\horrule##1##2##3%
        {\normalhskip##1\scratchdimen
         \vrule
           \!!height\boxrulewidth
           \!!width##2\scratchdimen
         \normalhskip##3\scratchdimen}%
      \normalvskip-3\scratchdimen
      \normalhbox to \ruledwidth
        {\verrule{3}{-1}\normalhss\verrule{3}{-1}}%
      \normalhbox to \ruledwidth
        {\horrule{-3}{2}{1}\normalhss\horrule{1}{2}{-3}}%
      \normalvskip-\boxrulewidth
      \vskip\ruledheight
      \ifdim\ruleddepth>\!!zeropoint\relax
        \normalvskip-.5\boxrulewidth
        \normalhbox to \ruledwidth
          {\horrule{-2}{1}{1}\normalhss\horrule{1}{1}{-2}}%
        \normalvskip-.5\boxrulewidth
        \vskip\ruleddepth
      \fi
      \normalvskip-\boxrulewidth
      \normalhbox to \ruledwidth
        {\horrule{-3}{2}{1}\normalhss\horrule{1}{2}{-3}}%
      \normalhbox to \ruledwidth
        {\verrule{-1}{3}\normalhss\verrule{-1}{3}}}%
   \dp\scratchbox=\ruleddepth      % This re-bounding is needed and 
   \ht\scratchbox=\ruledheight     % surfaced while typesetting continuous 
   \setbox\scratchbox=\normalhbox  % double culumns with pagecutmark 
     {\lower\ruleddepth\box\scratchbox}%
   \setbox#1=\ifhbox#1\normalhbox\else\normalvbox\fi
     {\normalhbox
        {\wd#1=\!!zeropoint 
         \box#1\relax
         \box\scratchbox}}%
   \wd#1=\ruledwidth
   \ht#1=\ruledheight
   \dp#1=\ruleddepth}

\def\cuthbox%
  {\normalhbox\bgroup
   \dowithnextbox{\makecutbox\nextbox\box\nextbox\egroup}%
   \normalhbox}

\def\cutvbox%
  {\normalvbox\bgroup
   \dowithnextbox{\makecutbox\nextbox\box\nextbox\egroup}%
   \normalvbox}

\def\cutvtop%
  {\normalvtop\bgroup
   \dowithnextbox{\makecutbox\nextbox\box\nextbox\egroup}%
   \normalvtop}

%
% \cutvbox
% \cutvtop
% \cuthbox
%
% \cutvbox{\ruledvbox{hello\par world \par \strut ziezo}}

\protect

\endinput