Persistent random steps decorations during beamer \uncover

Question

I'm using a random steps decoration with a path that appears through several uncover transitions. Currently the decoration is redrawn in each instance of the slide. How can I change this behavior. A minimal example follows. Thanks.

\documentclass[presentation]{beamer}  
\usepackage{tikz, pgf}  
\usetikzlibrary{decorations.pathmorphing}  
\begin{document}  
\begin{frame}  
\begin{center}  
\begin{tikzpicture}  
\uncover<1-3>{  
\fill [decorate, decoration={random steps,segment length=2pt,amplitude=2pt}] (0,0) ellipse (0.5cm and 0.4cm);  
}  
\end{tikzpicture}  
\end{center}  
\end{frame}  
\end{document} 

Answer 1

You can set the random seed each time you draw the ellipse, like so:

\documentclass[presentation]{beamer}
\usepackage{tikz, pgf}
\usetikzlibrary{decorations.pathmorphing}
\begin{document}

\begin{frame}
\begin{center}
\begin{tikzpicture}
\uncover<1-3>{
\pgfmathsetseed{1234} % Choose a four-digit number here
\fill [decorate, decoration={random steps,segment length=2pt,amplitude=2pt}] (0,0) ellipse (0.5cm and 0.4cm);
}
\end{tikzpicture}
\end{center}
\end{frame}

\end{document} 

The best part is that \pgfmathsetseed is local so outside this tikzpicture environment the pseudo-random number generator will behave as usual.

And by the way random.org is a cool place to get random numbers to use as seeds. Here's one just for you.