# [texhax] Beamer vertical jitter and vertical centering

Steve Schwartz s.schwartz at imperial.ac.uk
Fri Sep 8 14:19:51 CEST 2006

I give a lot of presentations in which I use beamer's columns to put,
say, itemized text in the left column and corresponding graphics in the
right. Often I use overlays to add the itemized text one by one and to
replace the graphics on the right as I step through. One of the
advantages of using columns is that beamer balances and vertically
centres the column material.

As predicted in the beamer documentation, this can lead to vertical
jitter (in this case in the itemized list). I attach a minimal example;
notice how the vertical position of the "> Item 1" jumps from the 1st to
2nd page.

The 3rd and 4th pages use beamer's solution to this problem, namely an
overprint environment. The jitter is absent, as the overprint area is
big enough to hold the biggest of the material inside it. HOWEVER, the
material is set at the top of the overprint area rather than in the
centre.

I've tried in vain to find a way to automatically move the overprint
material vertically within the overprint area. It IS possible to
manually insert a \vspace{..}\par after the onslide specifier. While I
guess it would be possible to write a macro to calculate the size of the
overprint area, the size of a given set of material, and hence the
amount of vspace to insert, that seems tedious.

So, does anyone have a better way?

Thanks
Steve

BTW, you can't begin a new group, e.g., with a curly brace, after the
onslide<..>, but you can have an immediate box. That is,

\onslide<+->{blah} produces different results to

\onslide<+->blah.

Some commands do this without an explicit curly brace. In particular,
\includegraphics does. Thus in my real presentations:

\onslide<+->\includegraphics{fig1}
\onslide<+->\includegraphics{fig2}

doesn't work: it positions fig2 underneath the position where it put
fig1. The same happens if you use the overlay-aware versions of
\includegraphics. A solution is to put everything in a box, e.g.:

\onslide<+->\mbox{\includegraphics{fig1}}
\onslide<+->\mbox{\includegraphics{fig2}}

Personally, I think this is a bug.
--
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Professor Steven J Schwartz      Phone: +44-(0)20-7594-7660
Space and Atmospheric Physics    Fax:   +44-(0)20-7594-7772
The Blackett Laboratory          E-mail: s.schwartz at imperial.ac.uk
Imperial College London          Office: Huxley 6M70
London SW7 2BW, U.K.             Web: http://www.sp.ph.ic.ac.uk/~sjs
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