TikZ - Change the color of a node "after" its declaration

Question

Is it possible to "change" the color of a node after its declaration ? Here is an example using forest even if my question is about TikZ.

\documentclass{article}
\usepackage{forest}
\newcommand\colorafter[2]{
    % ???
}
\begin{document}
\begin{forest}
    [
        [$A$, red % I don't want to use this.
            [$B$, name = nB]
            [$C$, name = nC]
        ]
        [$D$, blue % I don't want to use that.
        ]
    ]
    \colorafter{nB}{red}
    \colorafter{nD}{blue}
\end{forest}
\end{document}

I think this is not possible without major change of internal of forest. — muzimuzhi Z, Aug 05 '20 at 11:16
What is the point of this? Why do you need to declare first, then modify afterwards? — AndréC, Aug 05 '20 at 11:43
I would like to keep the logical definition of the tree and its decorations separated. I use more "advanced" formatting than the one in my example. — projetmbc, Aug 05 '20 at 12:34
While not what you're asking for, is defining and using styles an option? Certainly if you have a lot of options, if will reduce "clutter" in the tree. (By the way, when replying to a specific comment, you should ping the user with an at-sign, @AndréC wouldn't have been notified of your reply.) — Torbjørn T., Aug 05 '20 at 14:44
I agree with @Torbjørn T that the use of style is most appropriate. — AndréC, Aug 05 '20 at 15:23
You've probably seen it before, do e.g. \tikzset{foo/.style={draw=, blue, fill=cyan}, bar/.style={draw, dotted, yellow}} in the preamble and use just foo or bar in the tree. — Torbjørn T., Aug 06 '20 at 08:08

score 3 · Accepted Answer · edited Aug 26 '20 at 22:33

In the example, all nodes are created as blue nodes. The color of A (top left) is changed to red at the end. The bottom node is there only to suggest the path I have chosen.

The answer is for TikZ. The function \aftercolorof}[2]{... creates a new node with color #1 over node #2 with name #2-2 (in case you need it afterward).

It is based on the function given by @Henri Menke in How to access the label text of a node?.

\documentclass[11pt, border=1cm]{standalone}
\usepackage{tikz}
\makeatletter
\protected\def\tikz@fig@main#1{%
  \expandafter\gdef\csname labeltextof@\tikz@fig@name\endcsname{#1}%
  \iftikz@node@is@pic%
    \tikz@node@is@picfalse%
    \tikz@subpicture@handle{#1}%
  \else%
    \tikz@@fig@main#1\egroup%
  \fi}
\makeatother
\newcommand\labeltextof[1]{\csname labeltextof@#1\endcsname}
\newcommand{\aftercolorof}[2]{% #1 is the color, #2 us the node
  \path (#2.center) node[#1] (#2-2) {\labeltextof{#2}};
}
\begin{document}
\begin{tikzpicture}[
  every node/.style={draw, circle, color=blue, text=blue},
  spear/.style={->, very thin, shorten <=2pt, shorten >=2pt,}
  ]
  \path (0, 0) node (nA) {$A$};
  \path (2, 0) node (nB) {$B$};
\path (1, -2) node[label={
    [rectangle, text width=8em]-80:this is the node nC with nA's content
  }] (nC) {\labeltextof{nA}};
\path
  (nA) edge [spear, right] (nB)
  (nA) edge [spear, right] (nC);
% changing the color
  \aftercolorof{red}{nA}
\end{tikzpicture}
\end{document}

Here is an example showing that the solution works with forest.

\documentclass{article}
\usepackage{tikz}
\usepackage{forest}
\makeatletter
\protected\def\tikz@fig@main#1{%
  \expandafter\gdef\csname labeltextof@\tikz@fig@name\endcsname{#1}%
  \iftikz@node@is@pic%
    \tikz@node@is@picfalse%
    \tikz@subpicture@handle{#1}%
  \else%
    \tikz@@fig@main#1\egroup%
  \fi}
\makeatother
\newcommand\labeltextof[1]{\csname labeltextof@#1\endcsname}
\newcommand{\aftercolorof}[2]{% #1 is the color, #2 us the node
  \path (#2.center) node[#1] (#2-2) {\labeltextof{#2}};
}
\begin{document}
\begin{forest}
    [
        [$A$, name = nA
            [$B$]
            [$C$]
        ]
        [$D$, name = nD
        ]
    ]
    \aftercolorof{red}{nA}
    \aftercolorof{blue}{nD}
\end{forest}
\end{document}

TikZ - Change the color of a node "after" its declaration

1 Answers1

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