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beamer / doc / beamerug-twoscreens.tex

% Copyright 2007 by Till Tantau
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\section{Taking Advantage of Multiple Screens}

\label{section-twoscreens}

This section describes options provided by \beamer\ for taking
advantage of computers that have more than one video output and 
can display different outputs on them. For such systems, one video
output can be attached to a projector and the main presentation is
shown there. The second video output is attached to a small extra
monitor (or is just shown on the display of the computer) and shows,
for example, special notes for you. Alternatively, the two outputs
might be attached to two different projectors. One can then show the
main presentation on the first projection and, say, the table of
contents on the second. Or the second projection might show a version
translated into a different language. Or the seoncd projection might
alwyas show the ``previous'' slide. Or \ldots---I am sure you can
think of further useful things. 

The basic idea behind \beamer's support of two video outputs is the
following: Using special options you can ask \beamer\ to create a
\pdf-file in which the ``pages'' are unusually wide or high. By
default, their height will still be 128mm, but their width will be
192mm (twice the usual 96mm). These ``superwide'' pages will show 
the slides of the main presentation on the left and auxilliary
material on the right (this can be switched using appropriate
options, though hyperlinks will only work if the presentation is on
the left and the second screen on the right).

For the presentation you attach two screens to the system. The
windowing system believe that the screen is twice as wide as it
actually is. Everything the windowing system puts on the left half of
this big virtual screen is redirected to the first video output,
everything on the right half is redirected to the second video
output. 

When the presentation program displays the specially prepared
superwide \beamer-presentation, exactly the left half of the screen
will be filled with the main presentation, the right part is filled
with the auxilliary material---voil�. Not all presentation programs
support this special feature. For example, the Acrobat Reader 6.0.2 will
only use one screen in fullscreen mode on MacOS~X. You will have to
find out for yourself whether your display program and system support
showing superwise presentations stretching over two screens.

\beamer\ uses the package |pgfpages| to typeset two-screen
presentations. Because of this, your first step when creating a
two-screen presentation is to include this package:
\begin{verbatim}
\documentclass{beamer}
\usepackage{pgfpages}
\end{verbatim}

The next step is to choose an appropriate option for showing something
special on the second screen. These options are discussed in the
following sections.

One of the things these options do is to setup a certain
|pgfpages|-layout that is appropriate for two-screen
presentations. However, you can still change hte |pgfpages|-layout
arbitrarily, afterwards. For example, you might wish to enlarge the
virtual pages. For details, see the documentation of |pgfpages|.


\subsection{Showing Notes on the Second Screen}

The first way to use a second screen is to show the presentation
on the main screen and to show your notes on the second screen. The
option |show notes on second screen| can be used for this. It is
described on page~\pageref{command-notesonsecondscreen}.  



\subsection{Showing Second Mode Material on the Second Screen}

The second way to use the second screen is to show ``a different
vesion'' of the presentation on the second screen. This different
version might be a translation or it might just always be the current
table of contents.

To specify what is shown on the second screen, you can use a special
\beamer-mode called |second|. This mode behaves similar to modes like
|handout| or |beamer|, but its effect depends on the exact options
used:

\begin{beameroption}{second mode text on second screen}{|=|\meta{location}}
  This option causes the second screen to show the second mode
  material. The \meta{location} of the second screen can be |left|,
  |right|, |bottom|, or |top|.

  In detail, the following happens: When a new frame needs to be
  typeset, \beamer\ checks whether the special option |typeset second|
  is given. If not, the frame is typeset normally and the slides are
  put on the main presentation screen  (more precisely, on the logical
  |pgfpages|-page number zero). The second screen (logical page number
  one) shows whatever it showed before the frame was typeset.

  If the special frame option |typeset second| is given, after each
  slide of the frame the frame contents is typeset once more, but this
  time for the mode |second|. This results in another slide, which
  is put on the second screen (on logical page number one). Then the
  whole page is shipped out.

  The |second| mode behaves more like the |beamer| mode than
  other modes: Any overlay specification for |beamer| will also apply
  to |second| mode, unless an explicit |second| mode specification is
  also given. In particular, |\only<1-2>{Text}| will be shown on
  slides 1 and 2 in |second| mode, but only on the first slide in
  |handout| mode or |trans| mode.

  \example
\begin{verbatim}
\documentclass{beamer}
\usepackage{pgfpages}
\setbeameroption{second mode text on second screen}
\begin{document}
\begin{frame}[typeset second]
  This text is shown on the left and on the right.
  \only<second>{This text is only shown on the right.}
  \only<second:0>{This text is only shown on the left.}
\end{document}
\begin{frame}
  This text is shown on the left. The right shows the same as for the
  previous frame.
\end{frame}
\begin{frame}[typeset second]
  \alt<second>{The \string\alt command is useful for second
    mode. Let's show the table of contents, here: \tableofcontents}
  {Here comes some normal text for the first slide.}
\end{frame}
\end{document}
\end{verbatim}

  \example The following example shows how translations can be added
  in a comfortable way.
\begin{verbatim}
\documentclass{beamer}
\usepackage{pgfpages}
\setbeameroption{second mode text on second screen}
\DeclareRobustCommand\translation[1]{\mytranslation#1\relax}
\long\def\mytranslation#1|#2\relax{\alt<second>{#2}{#1}}
\title{\translation{Preparing Presentations|Vortr\"age vorbereiten}}
\author{Till Tantau}
\begin{document}
\begin{frame}[typeset second]
  \titlepage
\end{frame}
\begin{frame}[typeset second]
  \frametitle{\translation{This is the frame title.|Dies ist der Titel des Rahmens.}}
  \begin{itemize}
  \item<1-> \translation{First|Erstens}.
  \item<2-> \translation{Second|Zweitens}.
  \item<3-> \translation{Third|Drittens}.
  \end{itemize}
  \translation{Do not use line-by-line uncovering.|Man sollte Text nicht
  Zeile f\"ur Zeile aufdecken.}
\end{frame}
\end{document}  
\end{verbatim}
\end{beameroption}

In the last of the above example, it is a bit bothersome that the
option |typeset second| has to be added to each frame. The following
option globally sets this option:
\begin{beameroption}{always typeset second mode}{|=|\meta{true or false}}
  When this option is set to true, every following frame will have the
  option |typeset second| set to true.
\end{beameroption}


\subsection{Showing the Previous Slide on the Second Screen}

\begin{beameroption}{previous slide on second screen}{|=|\meta{location}}
  This option causes the second screen to show the previous slide that
  was typeset, unless this is overruled by a frame with the
  |[typeset second]| option set. The idea is that if you have two
  projectors you can always present ``the last two'' slides
  simultaneously and talk about them.

  Using this option will switch off the updating of external files
  like the table of contents.
\end{beameroption}



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