Scaling TikZ picture based on text size around the environment

Question

I'd like to scale a TikZ picture based on font size surrounding the environment.

For example...

\documentclass{standalone}                                                                                                   
                                                                                                                             
\usepackage{tikz}      
                                                                                                                             
\begin{document}                                                                                                             
                                                             
{                                                                                                                            
\begin{tikzpicture}                                          
  \draw (-1,-1) rectangle (1,1);                                                                                             
  \node at (0,0) {Hello world};                      
\end{tikzpicture}                                                                                                            
}                                 
                                                                                                                             
{                                                                                                                            
\Huge                             
\begin{tikzpicture}                                                                                                          
  \draw (-1,-1) rectangle (1,1);                   
  \node at (0,0) {Hello world};                                                                                              
\end{tikzpicture}                                  
}                                                                                                                            
                                                   
{                                                                                                                            
\tiny                                                                                                                        
\begin{tikzpicture}      
  \draw (-1,-1) rectangle (1,1);                                                                                             
  \node at (0,0) {Hello world};                                                                                              
\end{tikzpicture}      
}                                                                                                                            
                                                                                                                             
\end{document}      

I expect the second and third of these images to look like the first one, but scaled. Is it possible to use the x= and y= keys on the TikZ picture environment to allow for scaling of the image relative to the current font size?

---

EDIT

After a little more work I came up with the following...

\documentclass{standalone}

\usepackage{tikz}
\usepackage{printlen}

\newlength{\textsizenow}
\makeatletter
\newcommand{\refreshtextsizenow}{%
  \setlength{\textsizenow}{\f@size pt}
  }
\makeatother

\newcommand{\example}{%
  \refreshtextsizenow
  \begin{tikzpicture}[x=\textsizenow,y=\textsizenow]
    \draw (-3,-3) rectangle (3,3);
    \node at (0,0) {Hello world};
  \end{tikzpicture}
  }

\begin{document}

{
\Huge
\example
}

{
\huge
\example
}

{
\LARGE
\example
}

{
\Large
\example
}

{
\large
\example
}

{
\normalsize
\example
}

{
\small
\example
}

{
\footnotesize
\example
}

{
\scriptsize
\example
}

{
\tiny
\example
}

\end{document}

It uses \f@size to set a length before each image is drawn. I then use the x=...,y=... keys to set the coordinate size. This seems to get close to what I am trying to do. However, if the code above is compiled, the horizontal spacing between the text and the sides shrink as the text size gets smaller. The vertical spacing seems somewhat consistent. I expect both the horizontal and vertical spacing to stay the same. Is this possible to fix?

Answer 1

For font size dependent images, the following options can be used

\begin{tikzpicture}[x=1em,y=1em]
    \draw (-3,-3) rectangle (3,3);
    \node at (0,0) {Hello world};
\end{tikzpicture}

This sets the coordinate system so 1 is actually 1em. `em's are a unit whose value are relative to the current font size. Considerations such as font family must also be taken into account as kerning or symbol sizes may differ from one font family to another.