Use tikzpicture vector lengths to specify node dimension

Question

I would like to create a node with minimum width=αx, where x is the length of the x-coordinate vector specified in the tikzpicture environment, e.g. \begin{tikzpicture}[x=0.1cm,y=2.5ex]. Is this possible?

Answer 1

As suggested in this answer, you can define variables to set your x and y scales and a style for your node as in the following example:

\documentclass{article}
\usepackage{tikz}

\newcommand{\unitx}{1cm}
\newcommand{\unity}{1cm}

\tikzset{%
    box/.style 2 args = {%
        rectangle,
        draw,
        minimum width  = #1*\unitx,
        minimum height = #2*\unity
    },
    every tikzpicture/.append style = {
        x = \unitx,
        y = \unity
    }
}

\begin{document}

    \begin{tikzpicture}

        \node[box={2}{3}] at (0, 0) {Hello};

    \end{tikzpicture}

\renewcommand{\unitx}{5cm}
\renewcommand{\unity}{3cm}

    \begin{tikzpicture}

        \node[box={2}{3}] at (0, 0) {Hello};

    \end{tikzpicture}

\end{document}

With this, you impose a given scale on x and y for every tikzpicture environment and you define a style for a rectangle node with minimum width and minimum height based on this scale.

The scales are stored in the \unitx and \unity variables that you can redefine anywhere in your document to change the scale.

If you do not want to apply the scaling globally, remove the every tikzpicture argument of the \tikzset command and apply the scaling locally as in the following example:

\documentclass{standalone}
\usepackage{tikz}

\newcommand{\unitx}{2cm}
\newcommand{\unity}{1cm}

\tikzset{%
    box/.style 2 args = {%
        rectangle,
        draw,
        minimum width  = #1*\unitx,
        minimum height = #2*\unity
    }
}

\begin{document}

    \begin{tikzpicture}[x = \unitx, y = \unity]

        \node[box={2}{3}] at (0, 0) {Hello};

    \end{tikzpicture}

\end{document}