[Tex/LaTex] Draw a node as a square with TikZ

Question

I googled but cannot find a solution. Is that possible to draw a node with TikZ which will be a square and NOT a rectangle of arbitrary proportions?

Minimum working example can be something like this:

\documentclass{article}
\usepackage{tikz}

\begin{document}
    \begin{tikzpicture}
        \node at (0,0) [circle,draw] (c100) {$c_{100}$};
        \node at (3,0) [rectangle,draw] (v100) {$v_{100}$};
        \draw (c100) -- (v100);
    \end{tikzpicture}
\end{document}

While circle is perfectly round, rectangle is just a rectangle:

And I want it to be a square. I did not find any shape like square or so.

Answer 1

This is surprisingly difficult. In the following code, I've defined a custom node shape square that inherits from the rectangle shape, but forces its size to be square. Unfortunately, the inheritance mechanism doesn't allow redefinition of inherited saved anchors, so I had to copy some code from the TikZ rectangle definition.

On the plus side, it should be correct in all cases (defining different values for inner [xy]sep, minimum {width,height} and outer [xy]sep) and has all the anchors of the rectangle shape.

\documentclass[tikz,margin=5pt]{standalone}
\usepackage{tikz}

\makeatletter
% the contents of \squarecorner were mostly stolen from pgfmoduleshapes.code.tex
\def\squarecorner#1{
    % Calculate x
    %
    % First, is width < minimum width?
    \pgf@x=\the\wd\pgfnodeparttextbox%
    \pgfmathsetlength\pgf@xc{\pgfkeysvalueof{/pgf/inner xsep}}%
    \advance\pgf@x by 2\pgf@xc%
    \pgfmathsetlength\pgf@xb{\pgfkeysvalueof{/pgf/minimum width}}%
    \ifdim\pgf@x<\pgf@xb%
        % yes, too small. Enlarge...
        \pgf@x=\pgf@xb%
    \fi%
    % Calculate y
    %
    % First, is height+depth < minimum height?
    \pgf@y=\ht\pgfnodeparttextbox%
    \advance\pgf@y by\dp\pgfnodeparttextbox%
    \pgfmathsetlength\pgf@yc{\pgfkeysvalueof{/pgf/inner ysep}}%
    \advance\pgf@y by 2\pgf@yc%
    \pgfmathsetlength\pgf@yb{\pgfkeysvalueof{/pgf/minimum height}}%
    \ifdim\pgf@y<\pgf@yb%
        % yes, too small. Enlarge...
        \pgf@y=\pgf@yb%
    \fi%
    %
    % this \ifdim is the actual part that makes the node dimensions square.
    \ifdim\pgf@x<\pgf@y%
        \pgf@x=\pgf@y%
    \else
        \pgf@y=\pgf@x%
    \fi
    %
    % Now, calculate right border: .5\wd\pgfnodeparttextbox + .5 \pgf@x + #1outer sep
    \pgf@x=#1.5\pgf@x%
    \advance\pgf@x by.5\wd\pgfnodeparttextbox%
    \pgfmathsetlength\pgf@xa{\pgfkeysvalueof{/pgf/outer xsep}}%
    \advance\pgf@x by#1\pgf@xa%
    % Now, calculate upper border: .5\ht-.5\dp + .5 \pgf@y + #1outer sep
    \pgf@y=#1.5\pgf@y%
    \advance\pgf@y by-.5\dp\pgfnodeparttextbox%
    \advance\pgf@y by.5\ht\pgfnodeparttextbox%
    \pgfmathsetlength\pgf@ya{\pgfkeysvalueof{/pgf/outer ysep}}%
    \advance\pgf@y by#1\pgf@ya%
}
\makeatother

\pgfdeclareshape{square}{
    \savedanchor\northeast{\squarecorner{}}
    \savedanchor\southwest{\squarecorner{-}}

    \foreach \x in {east,west} \foreach \y in {north,mid,base,south} {
        \inheritanchor[from=rectangle]{\y\space\x}
    }
    \foreach \x in {east,west,north,mid,base,south,center,text} {
        \inheritanchor[from=rectangle]{\x}
    }
    \inheritanchorborder[from=rectangle]
    \inheritbackgroundpath[from=rectangle]
}

\begin{document}
    \begin{tikzpicture}
        \node[draw,square] {square with rectangular node text};
    \end{tikzpicture}
\end{document}