\ProvidesPackage{overlays}[2021/02/23 v2.12 Incremental slides]

% Copyright (C) 2021 Andreas Nolda

% Author: Andreas Nolda <andreas@nolda.org>
% Version: 2.12

% This work may be distributed and/or modified under the conditions of the LaTeX
% Project Public License, either version 1.3c of this license or (at your
% option) any later version. The latest version of this license is in
% http://www.latex-project.org/lppl.txt and version 1.3c or later is part of all
% distributions of LaTeX version 2005/12/01 or later.

% The following code is inspired by Matthias Meister's "present" package. It
% uses an algorithm by Martin Scharrer for testing numbers in numerical ranges
% (http://tex.stackexchange.com/q/19000). The code for saving counters between
% overlays as well as for overlays with verbatim content is taken from the
% "texpower" package, which in turn is based on Till Tantau's "beamer" package.

\RequirePackage{xcolor}
\RequirePackage{environ}
\RequirePackage{pgffor}

\def\s@vedcounters{}
\def\s@vedseries{}

\def\s@vecounters
  {\begingroup
     \def\@elt##1{\global\csname c@##1\endcsname\the\csname c@##1\endcsname}%
     \xdef\restores@vedcounters{\s@vedcounters}%
   \endgroup}

\def\s@veseries
  {\begingroup
     \def\@elt##1{\def\expandafter\noexpand\csname enit@resume@series@##1\endcsname%
                  {\csname c@##1i\endcsname\csname the##1i\endcsname}}%
     \xdef\restores@vedseries{\s@vedseries}%
   \endgroup}

\newcommand{\savecounterbetweenoverlays}[1]%
  {\expandafter\def\expandafter\s@vedcounters\expandafter{\s@vedcounters\@elt{#1}}}

\let\savebetweenoverlays\savecounterbetweenoverlays % for backward compatibility

\newcommand{\saveseriesbetweenoverlays}[1]%
  {\expandafter\def\expandafter\s@vedseries\expandafter{\s@vedseries\@elt{#1}}}

\savebetweenoverlays{page}
\savebetweenoverlays{equation}

\newcount\curoverl@y
\newcount\maxoverl@y

\NewEnviron{overlays}[1]%
  {\s@vecounters
   \s@veseries
   \maxoverl@y=#1%
   \curoverl@y=0%
   \loop
     \advance\curoverl@y by 1%
     \begingroup
     \BODY
     \endgroup
     \ifnum\curoverl@y<\maxoverl@y%
       \clearpage
       \restores@vedcounters
       \restores@vedseries
   \repeat}

\newwrite\verb@timfileout

\def\verb@timreadslide
  {\begingroup%
   \let\do\@makeother\dospecials%
   \count@=127%
   \@whilenum\count@<255 \do
     {\advance\count@ by 1%
      \catcode\count@=11}
   \@makeother\^^L
   \endlinechar`\^^M \catcode`\^^M=12 \processslidefirstline}

\newenvironment{fragileoverlays}[1]
  {\maxoverl@y=#1%
   \def\verb@timfilen@me{\jobname.vrb}%
   \immediate\openout\verb@timfileout=\verb@timfilen@me%
   \verb@timreadslide}
  {\immediate\closeout\verb@timfileout%
   \begin{overlays}{\maxoverl@y}
   \def\verbatim@nolig@list{\do\`\do\<\do\>\do\'} % don't make "," and "-" active
   \input{\verb@timfilen@me}%
   \end{overlays}}

\def\endfr@gileoverl@ys{\endgroup\end{fragileoverlays}}

{\catcode`\^^M=12\endlinechar=-1%
 \long\gdef\processslidefirstline#1^^M%
   {\def\overl@ystest{#1}%
    \ifx\overl@ystest\stopslidefirst%
      \let\next=\endfr@gileoverl@ys%
    \else
      \ifx\overl@ystest\@empty%
      \else%
        \@temptokena={#1}%
        \immediate\write\verb@timfileout{\the\@temptokena}%
      \fi%
      \let\next=\processslideline%
    \fi%
    \next}
 \long\gdef\processslideline#1^^M%
   {\def\overl@ystest{#1}%
    \ifx\overl@ystest\stopslide%
      \let\next=\endfr@gileoverl@ys%
    \else
      \immediate\write\verb@timfileout{#1}%
    \fi%
    \next}}

{\escapechar=-1\relax%
 \xdef\stopslide{\string\\end\string\{fragileoverlays\string\}}
 \xdef\stopslidefirst{\noexpand\end\string\{fragileoverlays\string\}}}

\newcount\overl@yspeca
\newcount\overl@yspecb

\def\@getoverl@yspecb-#1\relax%
  {\ifx\relax#1\relax
     \overl@yspecb=\maxoverl@y
   \else
     \overl@yspecb=#1\relax
   \fi}

\def\getoverl@yspecb%
  {\@ifnextchar\relax
     {\overl@yspecb=\overl@yspeca}%
     {\@getoverl@yspecb}}

\def\ifinoverl@yspec#1#2%
  {\global\let\inoverl@yspec\@secondoftwo
   \foreach \i in {#2}
     {\afterassignment\getoverl@yspecb
      \overl@yspeca=0\i\relax
      \pgfmathtruncatemacro\result{and((#1>=\overl@yspeca),(#1<=\overl@yspecb))}%
      \ifnum\result=1\relax
        \breakforeach
        \global\let\inoverl@yspec\@firstoftwo
      \fi}%
   \inoverl@yspec}

\long\def\overl@y#1#2#3{\ifinoverl@yspec{\curoverl@y}{#1}{#2}{#3}}

\newcommand{\only}[2]{\overl@y{#1}{#2}{\setbox1=\vbox{#2}}} % ensure side-effects of content (such as incremented counters)

\definecolor{background}{rgb}{1,1,1}

\@ifpackageloaded{pstricks}%
  {\def\pssetb@ckgroundcolor{\psset{linecolor=background}}}%
  {\def\pssetb@ckgroundcolor{\relax}}

\@ifpackageloaded{graphics}%
  {\def\hidegr@phics{\Gin@drafttrue}}%
  {\def\hidegr@phics{\relax}}

\newcommand{\visible}[2]{\overl@y{#1}{#2}{{\color{background}%
                                           \blendcolors{!0!background}%
                                           \pssetb@ckgroundcolor
                                           \hidegr@phics
                                           {#2}%
                                           \ifvmode
                                             \unskip % undo spurious space introduced by \color
                                           \fi}}}

\newcommand{\psvisible}[2]{\overl@y{#1}{#2}{{\pssetb@ckgroundcolor
                                             {#2}}}}

\definecolor{alert}{rgb}{1,0,0}
\@ifpackageloaded{pstricks}%
  {\def\psset@lertcolor{\psset{linecolor=alert}}}%
  {\def\psset@lertcolor{\relax}}

\newcommand{\alert}[2]{\overl@y{#1}{{\color{alert}%
                                     \psset@lertcolor
                                     {#2}%
                                     \ifvmode
                                       \unskip % undo spurious space introduced by \color
                                     \fi}}{#2}}

\newcommand{\psalert}[2]{\overl@y{#1}{{\psset@lertcolor
                                       {#2}}}{#2}}

\newcommand{\alertsoff}{\renewcommand{\alert}[2]{##2}%
                        \renewcommand{\psalert}[2]{##2}}

\newcommand{\overlaysoff}{\RenewEnviron{overlays}[1]%
                            {\maxoverl@y=##1%
                             \curoverl@y=##1%
                             \BODY}}