Beamer presentation without stretching of vertical spaces

Question

Currently I am updating and extending my beamer themes. Thereby I also want to solve a spacing problem, which is sometimes quite annoying.

Think of the following example:

\documentclass[t]{beamer}
%
\newcommand{\testcontent}[2]{%
    \frametitle{Frame #2}
    Text\medskip\par
    Itemize:%
    \begin{itemize}
    \item a%
    \item b%
    \item c%
    \end{itemize}
    \begin{figure}
    \framebox(300,#1){Height = #1 units}%
    \end{figure}
}
%
\begin{document}
%
\begin{frame}
\testcontent{150}{1}%
\end{frame}
%
\begin{frame}
\testcontent{50}{2}%
\end{frame}
%
\begin{frame}
\testcontent{150}{3}%
\vspace{0ex plus 1fil minus 1fil}%
\end{frame}
%
\end{document}

The example creates the following three frames. Open them in separate tabs to see the differences in vertical spacing:

In the first frame the defined height of the figure forces LaTeX to stretch (shrink) the vertical spaces of \medskip, itemize and figure. This can be seen if compared with the second frame, where the height of the figure is smaller and the vertical spaces are not stretched.

So I was looking for a solution to avoid the stretching of vertical spaces and consequently to have no jumping text lines when switching between frames. I found that someone redefined the corresponding lenghts to have no plus minus glue, but this did not work in my case or I missed to change some lengths.

So I came up with the \vspace{0ex plus 1fil minus 1fil} command in the third frame. This avoids stretching of the other verticals spaces, but gives no warning if the frame content does not fit on the frame. Another problem is, that I have to add this line manually to each frame end. I tried to automate this using \patchcmd for \beamer@collect@@body, but this also did not work.

Now to my questions:

1. Is there another way to avoid the described stretching of vertical spaces and to have constant vertical spaces independent of the frame content?
2. If there is no other solution then I used in the third frame above, is it possible to add the command automatically to each frame end?

Thank you very much for your help.

Answer 1

For "frames with only slightly varying content" I would not use separate frames, but slides of the same frame. To get the same shrinking between the slides, you can reserve the required space for your largest figure with the overlayarea environment.

\documentclass[t]{beamer}

\begin{document}

\begin{frame}
    \frametitle<1>{Frame 1}
    \frametitle<2>{Frame 2}
    Text\medskip\par
    Itemize:%
    \begin{itemize}
    \item a%
    \item b%
    \item c%
    \end{itemize}
    \begin{overlayarea}{300pt}{150pt}
      \begin{figure}
        \only<1>{\framebox(300,150){Height = 150 units}}
        \only<2>{\framebox(300,50){Height = 50 units}}
      \end{figure}
    \end{overlayarea}
\end{frame}

\end{document}

Answer 2

Here is an answer according to my answer here: https://tex.stackexchange.com/a/389647/120578

\documentclass[t]{beamer}
%
\usepackage{calc}
\newdimen\mycurrentheight
\newdimen\mymaxheight
\newdimen\myspace
\newdimen\zerodimen
\newsavebox{\mybox}

\def\keepHeight#1{
\setbox\mybox\vbox{#1}
\setlength{\mycurrentheight}{\ht\mybox+\dp\mybox}
\addspace{\mycurrentheight}
\usebox{\mybox}
\vskip \myspace
}


\def\addspace#1{
\ifdim\mycurrentheight>#1
\let\mymaxheight=\mycurrentheight
\let\myspace=\zerodimen
\else
\let\myspace=\zerodimen
\advance \myspace by \mymaxheight
\advance \myspace by -\mycurrentheight
\fi
}

\newcommand{\testcontent}[2]{%
    \frametitle{Frame #2}
    Text\medskip\par
    Itemize:%
    \begin{itemize}
    \item a%
    \item b%
    \item c%
    \end{itemize}
    \keepHeight{\begin{figure}
    \framebox(300,#1){Height = #1 units}%
    \end{figure}}
}
%
\begin{document}
%
\begin{frame}
\testcontent{140}{1}%
\end{frame}
%
\begin{frame}
\testcontent{50}{2}%
\end{frame}
%
\begin{frame}
\testcontent{140}{3}%
%\vspace{0ex plus 1fil minus 1fil}%
\end{frame}
%
\end{document}

I am not really sure if this is what you really want. I have created the command \keepheight{} and used it in your \testcontent.

I suppose we can manipulate it to your wants but I am not sure about that.

Give it a try!

Edit

Adding screenshots after OP's comment: