vertically align TikZ snippet in text

Question

When creating a TikZ snippet inside a figure caption, the snippet is never really aligned with the surrounding text. For example,

\documentclass{article}

\usepackage{tikz}

\begin{document}

\begin{figure}
\caption{%
  (\protect\tikz \protect\node [circle,draw=black,minimum width=1em]{};)
  }
\end{figure}

\end{document}

produces

I suppose it all looks alright if the circle sits comfortably on the base line. How to get it there?

Answer 1

Give the node some (invisible) content and a name and use the base (or any other desired) anchor for baseline; you can also pass explicit lengths to baseline for finer control. The following example shows both options (I also set inner sep=0pt for the second example):

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{figure}
\caption{%
  (\protect\tikz[baseline=(circ.base)] \protect\node[circle,draw=black,minimum width=1em] (circ) {\protect\phantom{a}};)
    (\protect\tikz[baseline=-0.7ex] \protect\node[circle,draw=black,inner sep=0pt,text width=1em] (circ) {\protect\phantom{a}};)}
\end{figure}

\end{document}

The result:

Answer 2

The math mode command \vcenter centers its material around the math axis:

\documentclass{article}

\usepackage{tikz}

\begin{document}
\listoffigures

\begin{figure}
\caption{%
  (%
    $\vcenter{\hbox{%
      \protect\tikz \protect\node [circle,draw=black,minimum width=1em]{};%
    }}$%
  )%
}
\end{figure}
\end{document}

The additional \hbox prevents, that \tikz starts a new paragraph inside \vcenter with a full line width. Both \vcenter and \hbox are robust and do not need \protect.