%D \module
%D   [       file=spac-grd,
%D        version=2009.10.16, % 1998.03.10, was core-grd.tex
%D          title=\CONTEXT\ Spacing Macros,
%D       subtitle=Grid Snapping,
%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. See mreadme.pdf for
%C details.

%D This module will be merged intio spac-ver.mkiv.

\writestatus{loading}{ConTeXt Spacing Macros / Grid Snapping}

% buff-ver.mkiv: halfline spacing
% strc-mat.mkiv: configure math grid (new code needed)
% page-one.mkiv: to be checked
% page-mul.mkiv: to be checked and redone
% page-sid.mkiv: to be checked
% page-set.mkiv: to be checked
% strc-not.mkiv: to be checked
% strc-ren.mkiv: to be checked
% strc-flt.mkiv: to be checked (captions, probably top/bottom)
% core-mis.mkiv: to be checked (placement, probbaly harmless)

\unprotect

%D Helpers:

\let\poplastnode\relax

\def\pushlastnode
  {\ifdim\lastskip=\zeropoint
     \ifnum\lastpenalty=\zerocount
       \ifnum\lastkern=\zerocount
         \let\poplastnode\relax
       \else
         \edef\poplastnode{\kern\the\lastkern\relax}\kern-\lastkern % untested
       \fi
     \else
       \edef\poplastnode{\penalty\the\lastpenalty\relax}\nobreak % untested
     \fi
   \else
     \edef\poplastnode{\vskip\the\lastskip\relax}\vskip-\lastskip % \removelastskip
   \fi}

%D Moved from supp-box:

%D \macros
%D  {startbaselinecorrection,baselinecorrection,
%D   showbaselinecorrection,offbaselinecorrection}
%D
%D Spacing around ruled boxes can get pretty messed up. The
%D next macro tries as good as possible to fix this.
%D
%D \startbuffer[1]
%D \startbaselinecorrection
%D \ruledhbox{Rule Brittanica}
%D \stopbaselinecorrection
%D \stopbuffer
%D
%D \typebuffer[1]
%D
%D The macros put some white space around the box:
%D
%D \getbuffer[1]
%D
%D A simple alternative is \type {\baselinecorrection}, which
%D only looks at the previous line.
%D
%D \startbuffer[2]
%D \baselinecorrection
%D \ruledhbox{Rule Brittanica}
%D \baselinecorrection
%D \stopbuffer
%D
%D \typebuffer[2]
%D
%D This time the last preceding line gets a correction,%
%D dependant on the depth.
%D
%D \getbuffer[2]
%D
%D One can make the correction visible by saying \type
%D {\showbaselinecorrection}. Part of the correction is
%D calculated from the dimensions of a~(. One can disble the
%D correction by calling \type {\offbaselinecorrection}.
%D
%D When visualize the first example looks like:
%D
%D {\showbaselinecorrection\getbuffer[1]}
%D
%D and the second one comes out as:
%D
%D {\showbaselinecorrection\getbuffer[2]}

% \definecolor[GridLineColor][red]
% \definecolor[GridTextColor][blue]

\let\thetopbaselinecorrection   \!!zeropoint
\let\thebotbaselinecorrection   \!!zeropoint
\let\thenegtopbaselinecorrection\!!zeropoint
\let\thenegbotbaselinecorrection\!!zeropoint

\def\setbaselinecorrections
  {\setbox0\hbox{\setstrut\strut}%
   \setbox2\hbox{(}%
   \dimen0\ht0\advance\dimen0 -\ht2
   \ifdim\dimen0<\zeropoint\dimen0\zeropoint\fi
   \dimen2\dp0\advance\dimen2 -\dp2
   \ifdim\dimen2<\zeropoint\dimen2\zeropoint\fi
   \edef\thetopbaselinecorrection   {\the\dimen0}\dimen0-\dimen0
   \edef\thebotbaselinecorrection   {\the\dimen2}\dimen2-\dimen2
   \edef\thenegtopbaselinecorrection{\the\dimen0}%
   \edef\thenegbotbaselinecorrection{\the\dimen2}}

\def\dotopbaselinecorrection   {\kern\thetopbaselinecorrection}
\def\dobotbaselinecorrection   {\kern\thebotbaselinecorrection}
\def\donegtopbaselinecorrection{\kern\thenegtopbaselinecorrection}
\def\donegbotbaselinecorrection{\kern\thenegbotbaselinecorrection}

\def\showbaselinecorrection
  {\def\dobaselinecorrection % visualization is not watertight!
     {\bgroup
\ifdim\prevdepth>\zeropoint\kern-\prevdepth\fi
      \setbox0\null
      \wd0\hsize
      \dp0\strutdp
      \nointerlineskip
      \forgetall
      \ruledvbox{\box0}%
      \egroup
      \prevdepth\strutdp}%
   \def\dotopbaselinecorrection
     {\hrule\!!height\thetopbaselinecorrection}%
   \def\dobotbaselinecorrection
     {\hrule\!!height\thebotbaselinecorrection}}

\def\dobaselinecorrection
  {\ifdim\prevdepth>\zeropoint\kern-\prevdepth\fi
   \kern\strutdp
   \prevdepth\strutdp}

\def\baselinecorrection
  {\endgraf
   \ifvmode
     \ifdim\prevdepth<\maxdimen
       \ifdim\prevdepth<\zeropoint \else
         \ifdim\prevdepth<\strutdepth \relax
           \pushlastnode
           \dobaselinecorrection
           \poplastnode
         \fi
       \fi
     \fi
   \fi}

\def\pagebaselinecorrection
  {\ifdim\pagegoal<\maxdimen
     \ifdim\pagetotal>\lineheight % or \topskip
       \scratchdimen\pagetotal
       \advance\scratchdimen\lineheight
       \ifdim\scratchdimen<\pagegoal
         \baselinecorrection
       \fi
     \fi
   \fi}

\unexpanded\def\startbaselinecorrection
  {\bgroup
   \let\stopbaselinecorrection\egroup
   \ifcase\baselinecorrectionmode
   \or % normal
     \baselinecorrection
     \ifvmode
       \setbox\scratchbox\vbox\bgroup\ignorespaces
       \let\stopbaselinecorrection\donormalstopbaselinecorrection
     \fi
   \or % off
   \or % force
     \baselinecorrection
     \ifvmode
       \setbox\scratchbox\vbox\bgroup\ignorespaces
       \let\stopbaselinecorrection\doforcedstopbaselinecorrection
     \fi
   \fi}

\let\stopbaselinecorrection\relax

\def\donormalstopbaselinecorrection % I have to check columns yet.
  {\egroup
   \topbaselinecorrection
   \box\scratchbox
   \botbaselinecorrection
   \egroup}

\def\doforcedstopbaselinecorrection % I have to check columns yet.
  {\egroup
   \forcedtopbaselinecorrection
   \box\scratchbox
   \forcedbotbaselinecorrection
   \egroup}

%D We do a bit more checking than needed. The pageborder check
%D is not needed, but I want to look the visualization as good
%D as possible too.

\chardef\baselinecorrectionmode\plusone

\def\onbaselinecorrection   {\chardef\baselinecorrectionmode\plusone  }
\def\offbaselinecorrection  {\chardef\baselinecorrectionmode\plustwo  }
\def\forcebaselinecorrection{\chardef\baselinecorrectionmode\plusthree}

%D \macros
%D  {topbaselinecorrection,botbaselinecorrection}
%D
%D The actual top and bottom corrections are implemented as:

\def\topbaselinecorrection
  {\ifvmode \ifdim\pagegoal<\maxdimen
     \forcedtopbaselinecorrection
   \fi \fi}

\def\forcedtopbaselinecorrection
  {\ifvmode
     \bgroup
     \setbaselinecorrections
     \whitespace
     \nointerlineskip
     \dotopbaselinecorrection
     \egroup
   \fi}

\def\botbaselinecorrection
  {\ifvmode
     \bgroup
     \setbaselinecorrections
     \dobotbaselinecorrection
     \allowbreak % new, otherwise problems when many in a row
     \prevdepth\strutdp
     \egroup
   \fi}

\let\forcedbotbaselinecorrection\botbaselinecorrection

\let\normalstartbaselinecorrection\startbaselinecorrection

\unexpanded\def\startbaselinecorrection
  {\ifgridsnapping
     \snaptogrid[v!normal]\vbox\bgroup
     \let\stopbaselinecorrection\egroup
   \else
     \normalstartbaselinecorrection
   \fi}

\protect \endinput