mathchoice and tikz's remember picture

Question

I have a macro to box (parts of) equations with tikz. I want to use mathchoice to remember the style and I want to label the tikz nodes for later reference. However, it does not work.

MWE:

\documentclass{article}

\usepackage[customcolors,shade]{hf-tikz}
\usepackage[]{tikz}

\tikzset{
  tbx-base/.style={ fill opacity=0.4, draw ,
  color=red, fill=red!80, },
}

\newcommand{\tbx}[3]{
  \mathchoice%
  {\tikz[remember picture] \node[#1] (#2) {\normalcolor{$\displaystyle#3$}};}
  {\tikz[remember picture] \node[#1] (#2) {\normalcolor{$\textstyle#3$}};}
  {\tikz[remember picture] \node[#1] (#2) {\normalcolor{$\scriptstyle#3$}};}
  {\tikz[remember picture] \node[#1] (#2) {\normalcolor{$\scriptscriptstyle#3$}};}
}

\newcommand{\tbxx}[3]{
  {\tikz[remember picture] \node[#1] (#2) {\normalcolor{$\displaystyle#3$}};}
}

\begin{document}
\[
  \tbx{tbx-base}{nodeEkin1}{A}
  +
  \tbxx{tbx-base}{nodeEkin2}{A}
\]
energy \tikz[remember picture,overlay, baseline=-.5ex]\node (nodeEkin01) {}; \\
energy \tikz[remember picture,overlay, baseline=-.5ex]\node (nodeEkin02) {};
\begin{tikzpicture}[remember picture,overlay]
  \path[-stealth,draw] (nodeEkin01) edge [out=0, in=-90] (nodeEkin1);
  \path[-stealth,draw] (nodeEkin02) edge [out=0, in=-90] (nodeEkin2);
\end{tikzpicture}
\end{document}

The arrow to the box created with \tbxx is correct, but \tbxx does not allow for the correct size (if, e.g. used in fractions or indices). \tbx allows for correct sizing, but not for correct referencing of the tikz nodes.

Is there a possibility to get the advantages of both macros?

Answer 1

The following example remembers the math style in a \label. Each argument of \mathchoice gets the same \label that is put in a deferred \write node. Later, when TeX makes its choice, only the correct \write node is executed.

Because the example uses references, two LaTeX runs are needed:

\documentclass{article}

\usepackage[customcolors,shade]{hf-tikz}
\usepackage[]{tikz}

\tikzset{
  tbx-base/.style={ fill opacity=0.4, draw ,
  color=red, fill=red!80, },
}

\usepackage{refcount}

\makeatletter
\newcounter{tbx}
\renewcommand*{\thetbx}{tbx@\the\value{tbx}}
\newcommand*{\tbxstyle}{%
  \refused{\thetbx}%
  \ifcase\getrefbykeydefault{\thetbx}{}{0} %
    \displaystyle
  \or\textstyle
  \or\scriptstyle
  \or\scriptscriptstyle
  \fi
}
\newcommand{\tbx}[3]{%
  \stepcounter{tbx}%
  \mathchoice
  {\def\@currentlabel{0}\label{\thetbx}}%
  {\def\@currentlabel{1}\label{\thetbx}}%
  {\def\@currentlabel{2}\label{\thetbx}}%
  {\def\@currentlabel{3}\label{\thetbx}}%
  {\tikz[remember picture] \node[#1] (#2) {\normalcolor{$\tbxstyle#3$}};}
}
\makeatother

\begin{document}
\[
  \tbx{tbx-base}{nodeEkin1}{A}
  _{\tbx{tbx-base}{nodeEkin2}{A}}
\]
energy \tikz[remember picture,overlay, baseline=-.5ex]\node (nodeEkin01) {};
\\
energy \tikz[remember picture,overlay, baseline=-.5ex]\node (nodeEkin02) {};
\begin{tikzpicture}[remember picture,overlay]
  \path[-stealth,draw] (nodeEkin01) edge [out=0, in=-90] (nodeEkin1);
  \path[-stealth,draw] (nodeEkin02) edge [out=0, in=-90] (nodeEkin2);
\end{tikzpicture}
\end{document}

Remarks:

• The math style is encoded as plain integer number, 0 for \displaystyle, 1 for \textstyle, ...

• The reference data is extracted with the help of package refcount.

• The label names are automatically generated with the help of counter tbx.

Package refmathstyle

For easier usage I have written a package refmathstyle that saves and references the current math style via macros \labelmathstyle and \refmathstyle. Until the next release of my bundle, the package is also available here (The .dtx file is embedded as PDF attachment. Then run tex refmathstyle.dtx (not latex) to extract the package file.)

The example simplifies to:

\documentclass{article}

\usepackage[customcolors,shade]{hf-tikz}
\usepackage[]{tikz}

\tikzset{
  tbx-base/.style={ fill opacity=0.4, draw ,
  color=red, fill=red!80, },
}

\usepackage{refmathstyle}
\newcommand{\tbx}[3]{%
  \labelmathstyle{}%
  {\tikz[remember picture] \node[#1] (#2) {\normalcolor$\refmathstyle{}#3$};}
}

\begin{document}
\[
  \tbx{tbx-base}{nodeEkin1}{A}
  _{\tbx{tbx-base}{nodeEkin2}{A}}
\]
energy \tikz[remember picture,overlay, baseline=-.5ex]\node (nodeEkin01) {};
\\
energy \tikz[remember picture,overlay, baseline=-.5ex]\node (nodeEkin02) {};
\begin{tikzpicture}[remember picture,overlay]
  \path[-stealth,draw] (nodeEkin01) edge [out=0, in=-90] (nodeEkin1);
  \path[-stealth,draw] (nodeEkin02) edge [out=0, in=-90] (nodeEkin2);
\end{tikzpicture}
\end{document}