Draw edges in background of transparent nodes

Question

This question is an extension of this one.

That question is about drawing a path in the background of nodes. There are three nodes equally separated on a line, and there is a straight line connecting all three in the background such that the middle one is not crossed visually. The nodes are filled, so the part of the path underneath the middle node is not visible (because it is behind the filling so to speak).

I want to achieve the same with transparent nodes (without filling) so that I can reuse the figure in different contexts (posters/slides) without the need to recolor the filling.

Here's my MWE (mostly borrowed from the same question)

\documentclass[border=20pt]{standalone}
\usepackage{tikz}
\pgfdeclarelayer{bg}
\pgfsetlayers{bg,main}
\begin{document}
\begin{tikzpicture}
  \node [draw] (foo) at (0,0) { foo };
  \node [draw] (bar) at (2,0) { bar };
  \node [draw] (baz) at (4,0) { baz };

  \begin{pgfonlayer}{bg}
    \draw [pink] (foo) -- (baz) ;
    \draw [cyan] (foo.25) -- (bar.155) (bar.25) -- (baz.155) ;
  \end{pgfonlayer}
\end{tikzpicture}
\end{document}

Which compiles to

The desired behavior can be achieved similarly to how the cyan line is drawn, but that notation is very long when there are more nodes and even longer when the line goes not through the vertical center, as here. Moreover, if I decide to add more nodes, I will have to correct all that code over and over again.

Is there any trick to produce a line like the cyan one by specifying its coordinates only at the outermost nodes?

Answer 1

Lines between nodes in ordered in line you can simpli draw, by use of join macro defined in the chains library. Also code is very simple, special if distances between nodes are equal:

\documentclass[border=20pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{chains,
                positioning}

\begin{document}
    \begin{tikzpicture}[
node distance = 10mm,
  start chain = going right,
   arr/.style = {draw=red, semithick},
N/.style = {draw, fill=gray, text opacity=1,
            on chain, join=by arr}
                        ]
  \node [N] (foo)   { foo };
  \node [N, fill opacity=0] (bar)   { bar };
  \node [N] (baz)   { baz };
  \node [N] (foo)   { foo };
  \node [N, fill opacity=0] (bar)   { bar };
  \node [N] (baz)   { baz };
    \end{tikzpicture}
\end{document}

Answer 2

Let me try with a combination of different other solutions (but mainly this one). It would only work with rectangular nodes though:

\documentclass[border=10pt]{standalone}
\usepackage{tikz}

\tikzset{
    clip even odd rule/.code={\pgfseteorule}, % Credit to Andrew Stacey 
    inverse clip/.style={
        clip,
        insert path={
            [clip even odd rule] {
               [reset cm] (-\maxdimen,-\maxdimen) rectangle (\maxdimen,\maxdimen)
            }
        }
    },
    cut out/.code={
        \begin{pgfinterruptboundingbox}
            \clip[inverse clip]
                (#1.north east) -- (#1.north west) -- (#1.south west) -- (#1.south east) -- cycle;
        \end{pgfinterruptboundingbox}
    }
}

\begin{document}
\begin{tikzpicture}

    \fill[yellow!50] (-1,-1) rectangle (7,3);

    \node[draw] (foo) at (0,0) { foo };
    \node[draw] (bar) at (2,0) { bar };
    \node[draw] (baz) at (4,0) { baz };
    
    \begin{scope}
        \draw[red, cut out={bar}] (foo) -- (baz);
    \end{scope}

    \node[draw] (Foo) at (0,2) { foo };
    \node[draw] (Bar) at (2,2) { bar };
    \node[draw] (Baz) at (4,2) { baz };
    \node[draw] (Qux) at (6,2) { qux };

    \begin{scope}
        \draw[red, cut out={Bar}, cut out={Baz}] (Foo.25) -- (Qux.155);
    \end{scope}

    % to show that scoping works
    \draw[cyan] (bar.south) -- (Bar.north);

\end{tikzpicture}
\end{document}

I hope that this does not break too many things. And maybe someone has an idea how to avoid the necessary scoping even ...