%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Module: ZzTeX Vertical Mode Facilities
%
% Synopsis:
%
% Author: Paul C. Anagnostopoulos
% Created: 21 September 1989
%
% Copyright 1989--2020 by Paul C. Anagnostopoulos
% under The MIT License (opensource.org/licenses/MIT)
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Interline Skip
% --------- ----
\def \nointerlineskip {%
\prevdepth = -1000pt}
\def \offinterlineskip {%
\baselineskip = -1000pt
\lineskip = 0pt
\lineskiplimit = \maxdimen}
% Vertical Skiping Environment
% -------- ------- -----------
% The following registers make up the vertical skiping environment.
\definecount{\zvskenvtype}{0} % Previous vertical skip type.
\definecount{\zvskenvpen}{0} % Previous columnbreak penalty.
\defineskip{\zvskenvreq}{0pt} % Previous required base-to-base skip.
\defineskip{\zvskenvskip}{0pt} % Previous actual skip amount.
\chardef \zvskenvdiscard = 0 % Just initialized the environment.
\chardef \zvskenvpar = 1 % Previous element was a paragraph.
\chardef \zvskenvabove = 2 % Just finished an above skip.
\chardef \zvskenvbelow = 3 % Just finished a below skip.
\chardef \zvskenvmath = 4 % Previous element was a paragraph ending
% with a math display.
\definecount{\zvskenvnopen}{20000\relax}
\let \noskip = \mindimen
% The vertical skiping environment is maintained in the vertical context.
\zdeclareeveryvcontext{\zvskenvvcontext}
\def \zvskenvvcontext {%
\zsavevcontext{\zvskenvtype=\the\zvskenvtype
\zvskenvpen=\the\zvskenvpen
\zvskenvreq=\the\zvskenvreq
\zvskenvskip=\the\zvskenvskip}%
\zvskpar
\global\zvskenvtype = \zvskenvdiscard}
% Base-to-Base Skiping
% ------------ -------
\declareeverypar{\zvskpar}
\def \zvskpar {%
\global\zvskenvtype = \zvskenvpar
\global\zvskenvpen = \zvskenvnopen
\global\zvskenvreq = \parskip \global\advance \zvskenvreq by \baselineskip
\global\zvskenvskip = 0pt}
%~ This command produces vertical space so that the base-to-base
%~ distance above the next element is equal to the *glue*. The
%~ space is preceded by the specified *penalty*. If there is a font
%~ change for the next element, it must be specified before this command.
\def \bbskipabove #1#2{% {penalty}{glue} %^vspace
\if \neqlp{\zvskenvtype}{\zvskenvdiscard}%
{\zvskprevmath{\parskip}{\baselineskip}%
\zparseglue #2\zmark
\setflag \znosk = {\dimeqlp{\zskipa}{\noskip}}%
\vpenalty{#1}%
\ifcase \zvskenvtype
\relax
\or
\if \znosk \zskipa = \zvskenvreq \fi
\or
\zskipa = \zvskenvreq
\or
\if \dimlssp{\zskipa}{\zvskenvreq}\zskipa = \zvskenvreq \fi
\or
\if \dimlssp{\zskipa}{\zvskenvreq}\zskipa = \zvskenvreq \fi
\fi
\if \notp{\dimzerop{\zvskenvskip}}\vskip -\zvskenvskip \fi
\zskipb = \zskipa
\advance \zskipb by -\parskip
\advance \zskipb by -\baselineskip
\vskip \zskipb
\if \notp{\znosk}%
\global\zvskenvtype = \zvskenvabove
\global\zvskenvreq = \zskipa
\fi
\global\zvskenvskip = \zskipb}%
\fi}
%~ This command produces vertical space so that the base-to-base
%~ distance below the current element is equal to the *glue*. The
%~ space is preceded by the specified *penalty*.
\def \bbskipbelow #1#2{% {penalty}{glue} %^vspace
\zvskbelow{#1}{#2}{\parskip}{\baselineskip}}
\def \bbskipbelowblock #1#2{% {penalty}{glue}
\zvskbelow{#1}{#2}{\enclosingparskip}{\enclosingbaselineskip}}
% This macro "returns" a value in \parnext:
% \noindent if next token does not start a new paragraph.
% empty if next token starts a new paragraph.
\def \bbskipbelowblockpar #1#2#3{% {token}{penalty}{glue}
{\setflag \znext = \false % Set \true if token starts new paragraph.
\ifcat \noexpand#1\relax \setflag \znext = \true \fi
\ifcat \noexpand#1\endgraf \setflag \znext = \true \fi
\ifcat \noexpand#1\egroup \setflag \znext = \true \fi
\ifcat \noexpand#1&\setflag \znext = \true \fi
\ifx #1\noindent \setflag \znext = \false \fi
\xdef \parnext {\if \znext \else \noindent \fi}%
\zskipa = #3\relax
\if \andp{\znext}{\dimneqlp{#3}{\noskip}}%
\tdimena = \zskipa
\advance \zskipa by -\tdimena
\advance \zskipa by \enclosingparskip
\advance \zskipa by \enclosingbaselineskip
\if \dimlssp{\zskipa}{#3}\zskipa = #3\fi
\fi
\zvskbelow{#2}{\zskipa}{\enclosingparskip}{\enclosingbaselineskip}}}
\def \zvskbelow #1#2#3#4{% {penalty}{glue}{parskip}{baselineskip}
{\zvskprevmath{#3}{#4}%
\zparseglue #2\zmark
\setflag \znosk = {\dimeqlp{\zskipa}{\noskip}}%
\vpenalty{#1}%
\ifcase \zvskenvtype
\zzerror{Skiping type is discard}%
\or
\if \znosk \zskipa = #3 \advance \zskipa by #4\fi
\or
\error{skipab}{A `skip below' follows a `skip above'}%
\or
\if \znosk \zskipa = \zvskenvreq \fi
\or
\if \dimlssp{\zskipa}{\zvskenvreq}\zskipa = \zvskenvreq \fi
\fi
\if \notp{\dimzerop{\zvskenvskip}}\vskip -\zvskenvskip \fi
\zskipb = \zskipa
\advance \zskipb by -#3%
\advance \zskipb by -#4%
\vskip \zskipb
\if \notp{\znosk}%
\if \neqlp{\zvskenvtype}{\zvskenvmath}% % Stay as math type so
\global\zvskenvtype = \zvskenvbelow % subsequent below skip
\fi % won't override.
\global\zvskenvreq = \zskipa
\fi
\global\zvskenvskip = \zskipb}}
\def \zvskprevmath #1#2{% {parskip}{baselineskip}
\if \eqlp{\mathdisplayprevgraf}{\prevgraf}%
\global\zvskenvtype = \zvskenvmath
\global\zvskenvpen = \mathdisplayprevpenalty
\global\zvskenvreq = \mathdisplayprevskip
\global\advance \zvskenvreq by #1
\global\advance \zvskenvreq by #2
\global\zvskenvskip = \mathdisplayprevskip
\global\mathdisplayprevgraf = -1\relax
\fi}
%~ This command forces the next base-to-base skip command
%~ regardless of the relationship between the previous element
%~ and the next one.
\def \forcenextbbskip {% %^vspace
\global\zvskenvtype = \zvskenvpar
\global\mathdisplayprevgraf = -1\relax}
\definecount{\zvpen}{0}
\def \vpenalty #1{% {penalty}
\zvpen = \if \emptyargp{#1}\breaknever \else #1\fi
\if \orp{\eqlp{\zvskenvpen}{\zvskenvnopen}}
{\eqlp{\zvpen}{\breaknever}}%
\columnbreak{\zvpen}%
\global\zvskenvpen = \zvpen\relax
\else \if \andp{\posp{\zvskenvpen}}{\gtrp{\zvpen}{\zvskenvpen}}%
\columnbreak{\zvpen}%
\global\zvskenvpen = \zvpen\relax
\fi\fi}
\def \forcenextpenalty {%
\global\zvskenvpen = \zvskenvnopen}
\def \repeatpenalty {%
\if \neqlp{\zvskenvpen}{\zvskenvnopen}%
\columnbreak{\zvskenvpen}%
\fi}
%~ This command inserts the specified amount of extra vertical space
%~ between the previous element and the next one.
\def \vspace #1{% {glue} %^vspace
\if \neqlp{\zvskenvtype}{\zvskenvdiscard}%
\zparseglue #1\zmark
\vskip \zskipa
\fi}
%~ This command inserts extra vertical space between the previous element
%~ and the next one. The space is measured in lines; a fractional number
%~ is allowed.
\def \linespace #1{\vspace{#1\baselineskip}}% {lines} %^vspace
\def \zparseglue #1#2\zmark{% {token}{tokens...}
\def \znext {#1}%
\def \zskip {\skip}%
\if \tokeqlp{\znext}{\zskip}%
\setskip \zskipa = #2\relax
\else
\zskipa = #1#2\relax
\fi}
% Top to Text Skipping
% --- -- ---- --------
% These commands use \zskipb so as not to screw up \fakepar.
\def \vsinkfromtypearea #1{% {sinkage}
\endgraf
\nobreak % So \fakepar can't break.
\fakepar % So \bbskipabove won't discard.
\vbox{}% % Force start of page if not already.
\kern -\pagetotal
\kern -\headerheight
\bbskipabove{\breaknever}{#1}}
\let \vsink = \vsinkfromtypearea
\def \vsinkfromtrim #1{% {sinkage}
\zskipb = #1\relax
\advance \zskipb by -\headmargin
\vsinkfromtypearea{\zskipb}}
\def \vsinkfromtextarea #1{% {sinkage}
\zskipb = #1\relax
\advance \zskipb by \headerheight
\if \topdeltaadjustment
\advance \zskipb by \topdelta
\fi
\vsinkfromtypearea{\zskipb}}
% Rules
% -----
\def \parrule #1#2{% {shift}{dimensions}
\endgraf
{\if \notp{\baselinetoprules}\zadjrule{#2}\fi
\hfuzz = 100pc
\noindent \hspace{#1}\vbox{\hrule height 0pt depth 0pt #2}\endgraf}}
\def \colorparrule #1#2#3{% {color}{shift}{dimensions}
\endgraf
{\if \notp{\baselinetoprules}\zadjrule{#3}\fi
\hfuzz = 100pc
\noindent \hspace{#2}%
\color{#1}\vbox{\hrule height 0pt depth 0pt #3}\endcolor \endgraf}}
\def \scotchrule #1#2#3{% {shift}{width}{height,gap,...}
\endgraf
{\hfuzz = 100pc
\commalist{\zscotchlist}{#3}%
\tcounta = 1\relax
\maplist{\zscotchb{#1}{#2}{##1}}{\zscotchlist}}}
\def \zscotchb #1#2#3{% {shift}{width}{dimension}
\if \andp{\eqlp{\tcounta}{1}}{\notp{\baselinetoprules}}%
\zadjrule{height #3 depth 0pt}%
\fi
\if \oddp{\tcounta}
\noindent \hspace{#1}\vbox{\hrule height #3 depth 0pt width #2}\endgraf
\parskip = 0pt
\else
\nobreak
\vspace{#3}%
\nointerlineskip
\fi
\increment \tcounta}
\def \zadjrule #1{% {dimensions}
\if \notp{\innermodep}%
\fakepar
\tdimena = \baselineskip
\advance \tdimena by -\prevdepth
\setbox \zboxa = \hbox{\vrule #1}%
\advance \tdimena by -\ht\zboxa
\vskip \tdimena
\vskip \topskip
\rule{height 0pt depth 0pt width 0pt}%
\penalty \breaknever
\vskip -\topskip
\parskip = 0pt \baselineskip = \ht\zboxa
\fi}
% Vertical Alignment
% -------- ---------
\def \bottomout {%
\hrule width 0pt height 0pt % Make sure \vskip isn't discarded.
\vskip 0pt plus 1filll}
% Counting Lines
% -------- -----
\definecount{\zlinect}{0}
\def \countlines #1#2#3#4{% {\count}{width}{font}{text}
\setbox\zboxa = \vbox{%
\hsize = #2%
#3%
#4\par}%
\global\zlinect = 0
\setbox\zboxa = \vbox{\unvbox\zboxa \zscanvbox}%
#1=\zlinect}
\def \zscanvbox {%
\loop
\setflag \zscanagain = \false
\setbox\zboxa = \lastbox
\if \hboxp{\zboxa}%
\global\increment \zlinect
\setflag \zscanagain = \true
\else\if \notp{\dimzerop{\lastskip}}%
\unskip
\setflag \zscanagain = \true
\else\if \notp{\dimzerop{\lastkern}}%
\unkern
\setflag \zscanagain = \true
\else\if \notp{\zerop{\lastpenalty}}%
\unpenalty
\setflag \zscanagain = \true
\fi\fi\fi\fi
\if \zscanagain \repeat}
% Special Boxes
% ------- -----
\definedimen{\zibprevdepth}{0pt}
\long\def \interjectbox #1#2{% {right-shift}{content}
{\zibprevdepth = \prevdepth
\penalty \breaknever
\nointerlineskip
\moveright #1 \vbox to 0pt{%
\zpushvcontext
#1\relax
\zpopvcontext}%
\prevdepth = \zibprevdepth}}
\long\def \smashbox #1{%
\vbox to 0pt{%
#1\relax
\vss}}