Tikz equivalent of PSTricks commands ncbar and rnode

Question

Motivated by this recent question, I tried to cook up a tikz based solution using the code provided in the answer to this question. More precisely, I tried to cook up equivalents of the pstricks \rnode and \ncline commands in tikz. This is what I got:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\newsavebox{\tempbox}

\newcommand{\tikznode}[2]{\relax\ifmmode\savebox{\tempbox}{\ensuremath{#2}}
\makebox[\wd\tempbox]{\tikz[overlay,remember picture,baseline=-0.8ex]%
 \node[minimum width=\wd\tempbox] (#1) {\ensuremath{#2}};}
\else\savebox{\tempbox}{#2}
\makebox[0.5\wd\tempbox]{\tikz[overlay,remember picture,baseline=-0.8ex,minimum width=\wd\tempbox]%
 \node[minimum width=\wd\tempbox] (#1) {#2};}\fi}

\tikzset{
    ncbar angle/.initial=-90,
    ncbar/.style={
        to path=(\tikztostart)
        -- ($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)
        -- ($(\tikztotarget)!($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztostart)$)
        -- (\tikztotarget)
    },
    ncbar/.default=0.5cm
}

\begin{document}
blabla \tikznode{A}{A}\tikznode{B}{B}\tikznode{C}{C} blabla
\tikznode{X}{X}\tikznode{Y}{Y}\tikznode{Z}{Z} blabla
\tikz[overlay,remember picture]{\draw[->] (A) to [ncbar=0.4] (X);}%
\tikz[overlay,remember picture]{\draw[->] (B) to [ncbar=0.5] (Y);}%
\tikz[overlay,remember picture]{\draw[->] (C) to [ncbar=0.6] (Z);}%
\end{document}

It produces:

which looks not completely unreasonable. However, it seems unreasonably complicated and I assume that there is a much more elegant and stable solution. For instance, I need to shift the baseline by hand using baseline=-0.8ex. This doesn't seem right. I also need to compute the width of the text and multiply it by an arbitrary factor of 0.5, which again appears odd. Last but not least, I have to distinguish between math and text modes. (Yes, I know that in principle there is \mathchoice that may be used, but I feel that I've chosen an unnecessarily complicated approach, so I refrained from building this in.) My question is if someone knows how to make this more elegant and, in particular, stable.

Answer 1

I would probably do

\newcommand{\tikznode}[2]{%
\ifmmode%
\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {$#2$};%
\else
\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {#2};%
\fi}

By setting the baseline to the base anchor of the node, you don't have to use some specific value. With inner sep=0pt you wont get any extra space around the text in the node.

Note also that I removed the overlay option. That option means that you get a zero-size bounding box, which you don't want here.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}

\newcommand{\tikznode}[2]{%
\ifmmode%
\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {$#2$};%
\else
\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {#2};%
\fi}

\tikzset{
    ncbar angle/.initial=-90,
    ncbar/.style={
        to path=(\tikztostart)
        -- ($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)
        -- ($(\tikztotarget)!($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztostart)$)
        -- (\tikztotarget)
    },
    ncbar/.default=0.5cm
}

\begin{document}
blabla \tikznode{A}{A}$\tikznode{B}{B}$\tikznode{C}{C} blabla
\tikznode{X}{X}\tikznode{Y}{Y}\tikznode{Z}{Z} blabla
\begin{tikzpicture}[overlay,remember picture]
\draw[->] (A) to [ncbar=0.4] (X);
\draw[->] (B) to [ncbar=0.5] (Y);
\draw[->] (C) to [ncbar=0.6] (Z);
\end{tikzpicture}
\end{document}

If you want to implement \mathchoice in this, you get problems, because all the four different choices are typeset. Hence, the naive implementation of

\newcommand{\tikznode}[2]{%
\ifmmode%
\mathchoice
  {\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {$\displaystyle #2$};}%
  {\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {$\textstyle #2$};}%
  {\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {$\scriptstyle #2$};}%
  {\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {$\scriptscriptstyle #2$};}%
\else
\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {#2};%
\fi}

doesnt't work, because the node name will always refer to the scriptscript-version, which isn't used at all in the three other styles. So for the example above, where the B is in textstyle, you get an arrow pointing out of the page.

Perhaps unsurprisingly though, someone has wondered about that problem before, and Heiko Oberdiek provided a solution to it in mathchoice and tikz's remember picture. The refmathstyle package he made has not yet been published on CTAN though, and the link to it in that answer is dead, so here is the non-package version:

\documentclass{article}
\usepackage{tikz}
\usepackage{refcount}
\usetikzlibrary{calc}

% from https://tex.stackexchange.com/questions/122415/mathchoice-and-tikzs-remember-picture
\makeatletter
\newcounter{tikznode}
\renewcommand*{\thetikznode}{tikznode@\the\value{tikznode}}
\newcommand*{\tikznodestyle}{%
  \refused{\thetikznode}%
  \ifcase\getrefbykeydefault{\thetikznode}{}{0} %
    \displaystyle
  \or\textstyle
  \or\scriptstyle
  \or\scriptscriptstyle
  \fi
}
\newcommand{\tikznode}[2]{%
\ifmmode%
  \stepcounter{tikznode}%
  \mathchoice
  {\def\@currentlabel{0}\label{\thetikznode}}%
  {\def\@currentlabel{1}\label{\thetikznode}}%
  {\def\@currentlabel{2}\label{\thetikznode}}%
  {\def\@currentlabel{3}\label{\thetikznode}}%
  \tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {$\tikznodestyle #2$};
\else
  \tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {#2};%
\fi}
\makeatother

% from https://tex.stackexchange.com/questions/55068/is-there-a-tikz-equivalent-to-the-pstricks-ncbar-command
\tikzset{
    ncbar angle/.initial=-90,
    ncbar/.style={
        to path=(\tikztostart)
        -- ($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)
        -- ($(\tikztotarget)!($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztostart)$)
        -- (\tikztotarget)
    },
    ncbar/.default=0.5cm
}

\begin{document}
blabla
$\displaystyle\tikznode{A}{A}\textstyle\tikznode{B}{B}_{\tikznode{C}{C}_{\tikznode{D}{D}}}$
blabla
\tikznode{X}{X}\tikznode{Y}{Y}\tikznode{Z}{Z}\tikznode{W}{W}
blabla
\begin{tikzpicture}[overlay,remember picture]
\draw[->] (A) to [ncbar=0.4] (X);
\draw[->] (B) to [ncbar=0.5] (Y);
\draw[->] (C) to [ncbar=0.6] (Z);
\draw[->] (D) to [ncbar=0.6] (W);
\end{tikzpicture}
\end{document}

Answer 2

Since it's buried in the comments on Torbjørn's answer, this is just to note that this is now a part of the tikzmark package, and correctly handles the different math modes. Here's a demo:

\documentclass{article}
%\url{https://tex.stackexchange.com/q/402462/86}
\usepackage{tikz}
\usetikzlibrary{tikzmark,calc}
\tikzset{
    ncbar angle/.initial=-90,
    ncbar/.style={
        to path=(\tikztostart)
        -- ($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)
        -- ($(\tikztotarget)!($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztostart)$)
        -- (\tikztotarget)
    },
    ncbar/.default=0.5cm
}
\begin{document}
blabla \tikzmarknode{A}{A}(\tikzmarknode{B}{B}^{\tikzmarknode{C}{C}}) blabla
\tikzmarknode{X}{X}\tikzmarknode{Y}{Y}\tikzmarknode{Z}{Z} blabla
\begin{tikzpicture}[overlay,remember picture]
\draw[->] (A) to [ncbar=0.4] (X);
\draw[->] (B) to [ncbar=0.5] (Y);
\draw[->] (C) to [ncbar=0.6] (Z);
\end{tikzpicture}
\end{document}

The lines from C to Z are angled because the bottoms of the nodes are at different levels. I don't know what the original PSTricks ncline does in that circumstance so I left that code as it is in Torbjørn's answer.