%% file: twin.txs  (TeXsis version 2.16)
%  $Revision: 16.0 $  :  $Date: 1993/07/26 22:59:46 $  :  $Author: myers $
%======================================================================*
% TWINOUT -- two pages side by side on one piece of paper
%
% \twinout redefines TeX's \output routine to put two pages side-by-side
% on one piece of paper, in landscape format. By default the height/width
% ratio of \vsize to \hsize is preserved, unless this would make the
% two pages overlap.  In that case the new \hsize is adjusted to give 
% a "reasonable" gutter between the two pages.  (For example, the first
% method works for A4 paper, but fails for U.S. letter size, so then the
% second method is used.)
%
% In some cases the defaults will not give you what you want. 
% If you don't like the way that \twinout sets the sizes of the pages
% you can adjust them to your liking AFTER you have invoked \twinout.
% \hsize is the width of an individual page, \vsize is the height of
% either page, and \twinhsize is the width of both pages across the
% length of the paper (the default is the \vsize in effect before you
% invoked \twinout).  The \hoffset and \voffset can also be adjusted.
% The default is to set \hoffset=-0.10in, which is a reasonable place to
% start; \voffset is unchanged.
%
% Typestyles are NOT changed, you have to do that yourself.   
%
% An example showing both page size and typestyle selection is:
%
%       \twinout
%       \twinhsize=9in \vsize=6.95in \hsize=4.36in \hoffset=-0.5in
%       \tenpoint
%
% These macros are patterned after similar macros in Harvmac by 
% Paul Ginsparg, as well as the plain.tex \output routines, but this 
% is a total rewrite by Eric Myers <myers@lifshitz.ph.utexas.edu>.
%
% Dependencies: \LandscapeSpecial should be defined in TXSsite.tex, but 
% you can make your own definition before twin.txs is read in, or you
% can do without it and give dvips the "-t landscape" flag.  Other than
% worrying about that, this can be used by itself with plain.tex.  
%
% This file is a part of TeXsis, a TeX macro package for Physicists
% (C) copyright 1993 by Eric Myers and Frank Paige 
%======================================================================*
\message{- two pages on one}
\catcode`@=11           % @ is a letter here to hide the inner workings

\newbox\@leftpage       % box to hold left page while building right page
\newdimen\twinhsize     % width of both pages together across the page


% \LandscapeSpecial is the \special command that puts your laser printer
% in "landscape" mode, i.e. printing sideways.  If it is not already
% defined (in TeXsis this is done in TXSsite.tex) then the default 
% is for Tom Rokicki's dvips.

\ifx\undefined\LandscapeSpecial % is there no definition? then use
  \def\LandscapeSpecial{\special{papersize=11in,8.5in}}% dvips version
\fi


% \twinout just sets up the column flag (to start in Left column),
% sets the new \hsize and \vsize and changes \output.

\def\twinout{% change \output to get two pages on one
   \global\let\@LR=L                    % begin in left column
   \twinsize                            % set paper size to default
   \output={\twinoutput}}               % redefine \output


% \twinsize sets the page size for twin page output from the
% current settings of \vsize and \hsize, preserving their ratio.
% If h and v are the original horizontal and vertical sizes then the
% width of a new page is w = h*(h/v).  [Since TeX stores dimensions
% in scaled points (65536sp=1pt) we have to be careful to rescale
% from sp to pt to avoid arithmetic overflow.]  If the columns would
% overlap then a smaller \hsize is chosen such that there is a
% reasonable gutter between the two pages.

\def\twinsize{% set page sizes for twin page output
   \twinhsize=\vsize                    % two pages across one rotated page
   \vsize=\hsize                        % height of page is width of paper
   \hoffset=-0.1in                      % also adjust offset a bit
% now compute default \hsize from \hsize/\vsize ratio
   \divide\hsize by 65536               % convert sp to pt for calculations
   \multiply\hsize by \hsize            % h^2 in points
   \dimen@=\twinhsize \divide \dimen@ by 65536 % v in pt from sp
   \divide\hsize by \dimen@             % w = h * (h/v)
   \multiply\hsize by 65536             % convert pt back to sp
% also compute candidate \hsize based on \twinhsize with a reasonable gutter
   \dimen@=-\vsize \divide\dimen@ by 13 % gutter width computed from height
   \advance\dimen@ by \twinhsize        % width of page minus gutter
   \divide\dimen@ by 2                  % divide by 2 to get column width
   \ifdim\dimen@<\hsize \hsize=\dimen@\fi} % choose smaller \hsize


% \twinoutput builds the page as plain.tex does, but with a modified 
% \shipout to collect the left page first, then put both pages out together

\def\twinoutput{% modified version of \plainoutput for two-on-one printing
  \twinshipout{\vbox{\makeheadline\pagebody\makefootline}}%
  \advancepageno
  \ifnum\outputpenalty>-\@MM \else\dosupereject\fi}


% \twinshipout takes a \vbox, as \shipout does, but for the left page
% it saves it temporarily.  When the right page is given it puts the two
% side by side and ships them out together.

\def\twinshipout#1{% modified version of \shipout for two-on-one  printing
   \if L\@LR                            % left page?
      \global\setbox\@leftpage=#1       % save the box for left page
      \message{[\the\pageno]}%          % fake [page number] in log
      \global\let\@LR=R                 % set flag for next (right) page
   \else                                % right page?
      \shipout\vbox{\LandscapeSpecial   % force landscape on every page
        \hbox to \twinhsize{\box\@leftpage\hfil{#1}}}% 2 pages side by side
      \global\let\@LR=L                 % set flag back to left page
   \fi}

\catcode`@=12                           % @ is no longer a letter
% >>> EOF twinout.txs <<<