How can I make scaling affect TikZ-pics within a tikzpicture?

Question

I want to have "global scaling" in a TikZ picture, which also affects all pics defined within a tikzpicture environment. MWE:

\documentclass[tikz, border=2mm]{standalone}
\begin{document}
    \begin{tikzpicture}[scale=0.5]    
        \draw [green] (0,0) rectangle (10,10);
        \tikzset{square/.pic={\draw [red] (0,0) rectangle (10,10);}}
        \draw (0,0) pic {square};
    \end{tikzpicture}
\end{document}

Why does the red square defined in square not fit the green square drawn within the tikzpicture? How can I make the scaling global, affecting all pics defined within it? I would like to avoid scaling every pic by hand.

Answer 1

transform shape is your friend. Usually, stuff like nodes (and obviously pics) are not scaled. With transform shape, you can enforce this. Note that this also scales text.

\documentclass[tikz, border=2mm]{standalone}
\begin{document}
    \begin{tikzpicture}[scale=0.5, transform shape] % <--- Here!  
        \draw [green] (0,0) rectangle (10,10);
        \tikzset{square/.pic={\draw [red] (0,0) rectangle node[midway, transform shape = false] { Foo } (10,10);}} % note the inserted, not transformed text node
        \draw (0,0) pic {square};
    \end{tikzpicture}
\end{document}