This is due to an unfortunate interaction between how overprint works and the center environment. Because the center environment is in force when overprint is figuring out which text to use, the text gains some extra horizontal space (to centre it). But when overprint sets the text, it modifies it in such a way that TeX adds yet more space to centre it again. Net result being that the text gets shoved too far over to the right. Thanks to David Carlisle and Herbert, I can offer two ways to "cancel" the effect. Both get rid of the centre effect when the overprint environment is doing its stuff.
Note that due to the way overprint works, to get the contents centred, you have to add in \centering to each piece. There's no other way to do that. I've assumed, in the below, that that is what you want to happen.
\documentclass[transparent]{beamer}
\usepackage[english]{babel}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{positioning}
\makeatletter
\def\normaljustify{%
\let\\\@centercr
\rightskip\z@skip
\leftskip\z@skip%
\parfillskip=0pt plus 1.0fil\relax
}
\makeatother
\begin{document}
\begin{frame}%
\begin{center}
\begin{tikzpicture}[every node/.style={draw}]
\onslide<+->{\node(a){Herbert's code};}
\onslide<+->{\node(b)[below=of a,align=center]{%
\normaljustify
\begin{overprint}[4cm]
\onslide<+>
\centering
$a=b$
\onslide<+>
\centering
$b=c$
\onslide<+>
\centering
$c=d$
\end{overprint}
};}
\node(c)[below=of b]{test2};
\end{tikzpicture}
\begin{tikzpicture}[every node/.style={draw}]
\onslide<+->{\node(a){David Carlisle's code};}
\onslide<+->{\node(b)[below=of a,align=center]{%
\begin{minipage}{\textwidth}%
\begin{overprint}[4cm]
\onslide<+>
\centering
$a=b$
\onslide<+>
\centering
$b=c$
\onslide<+>
\centering
$c=d$
\end{overprint}%
\end{minipage}
};}
\node(c)[below=of b]{test2};
\end{tikzpicture}
\end{center}
\end{frame}%
\end{document}
I'm not sure which of the two to prefer. One thing to note about David's method (with the additional minipage) is that if you put anything "normal" (such as bare text) inside that minipage then it will have width \textwidth which is not desirable.
The simplest way IMHO is to typeset the inner tikzpicture in a savebox outside the other tikzpicture and then use the box inside the node.
This way no settings of the parent tikzpicture will be picked up, because the inner one is already rendered.
\documentclass{report}
\usepackage{tikz}
\usetikzlibrary{positioning}
\newsavebox\mybox
\begin{document}
\begin{lrbox}{\mybox}
\begin{tikzpicture}
\draw [step=0.25cm,lightgray,very thin] (0,0) grid (2.5,1.5);
\draw [draw,->,ultra thick] (0,0.0) -- (0,1.5);
\draw [draw,->,ultra thick] (0,0.0) -- (2.5,0);
\draw [fill=blue!20!white,ultra thick,overlay] (0.2,0) ..controls
(0.5,2.2) and (1,0.1) .. (2,0);
\end{tikzpicture}
\end{lrbox}
\begin{tikzpicture}[node distance=2em]
\node(pdf){\usebox\mybox};
\node [rectangle,draw, right=of pdf] (cfd) {Nonlinear Flow Solution};
\path[draw,->] (pdf) -- (cfd);
\end{tikzpicture}
\end{document}
If you want to do this using a macro:
\documentclass{report}
\usepackage{tikz}
\usetikzlibrary{positioning}
\newsavebox\mybox
\begin{lrbox}{\mybox}
\normalfont% to ensure that the font is fully set up
\begin{tikzpicture}
\draw [step=0.25cm,lightgray,very thin] (0,0) grid (2.5,1.5);
\draw [draw,->,ultra thick] (0,0.0) -- (0,1.5);
\draw [draw,->,ultra thick] (0,0.0) -- (2.5,0);
\draw [fill=blue!20!white,ultra thick,overlay] (0.2,0) ..controls
(0.5,2.2) and (1,0.1) .. (2,0);
\end{tikzpicture}
\end{lrbox}
\newcommand\mypdfimage{\usebox\mybox}
\begin{document}
\begin{tikzpicture}[node distance=2em]
\node(pdf){\mypdfimage};
\node [rectangle,draw, right=of pdf] (cfd) {Nonlinear Flow Solution};
\path[draw,->] (pdf) -- (cfd);
\end{tikzpicture}
And again:
\begin{tikzpicture}[node distance=2em]
\node(pdf){\mypdfimage};
% [..]
\end{tikzpicture}
\end{document}
But here the macro is just a short-cut, you can use \usebox\mybox directly if you don't mind.
Best Answer
The problem with your code is that the
\tikzcommand itself is not overlay-aware. (I think that it would be quite difficult to make it so.) So the\tikzstuff is getting executed on every slide, but theyyynode doesn't exist until the second slide so it doesn't know what to do with it. If you shift the<2>to the\drawinstead then it works.