includegraphics in tikz node

Question

I wanted to do this:

but write with a variable width:

\documentclass[tikz,border=5mm]{standalone}
\begin{document}
\def\mywidth{2cm}
\tikz\node[circle,draw,minimum size=1.2*\mywidth
           text=white,
           path picture={
               \node at (path picture bounding box.center){
                   \includegraphics[width=1.2\mywidth]{frog}
               };
           }]{I'm watching you!};
\end{document}

Why does this not work? The includegraphics command does not display the image in 1.2\mywidth but some arbitrary size. The circle is the right size.

Second examples

Code 1

\documentclass[tikz,border=5mm]{standalone}
\begin{document}

\def\firstwidth{1cm}
\def\secondwidth{2\firstwidth}

\tikz\node[circle,draw,minimum size=\firstwidth,
           path picture={
               \node at (path picture bounding box.center){
                   \includegraphics[width=\firstwidth]{blackbox.png}
               };
           }]{};
\end{document}

Result 1

Code 2

\documentclass[tikz,border=5mm]{standalone}
\begin{document}

\def\firstwidth{1cm}
\def\secondwidth{2\firstwidth}

\tikz\node[circle,draw,minimum size=\firstwidth,
           path picture={
               \node at (path picture bounding box.center){
                   \includegraphics[width=0.5\secondwidth]{blackbox.png}
               };
           }]{};
\end{document}

Result 2 (should be like Result 1)

Can you make a sketch what you like to obtain? And where you like to place your frog on page? — Zarko, Dec 02 '15 at 20:10
@Zarko: It's supposed to look as in the link. Difference only in size. — Make42, Dec 02 '15 at 20:27
@percusse: Within the node text I should be in standard LaTeX syntax. Of course I had tried anyway and failed. — Make42, Dec 02 '15 at 20:28
I can reproduce image as it is given link with the following two changes: minimum size=\mywidth and \includegraphics[width=4.4\mywidth]{...}. For test I use example-image from graphicx package. — Zarko, Dec 02 '15 at 20:37
@Zarko: I added another example with images - maybe that clarifies the situation. — Make42, Dec 02 '15 at 21:10
Instead to use \def\mywidth{2cm} try to use \newlength\mywidth \setlength\mywidth{2cm} and similarly at other lengths. This work fine at me. — Zarko, Dec 02 '15 at 21:26
@user49283, see my answer. Let me know, if it solve (at least a part of) your problem. — Zarko, Dec 02 '15 at 22:29

score 4 · Accepted Answer · answered Dec 02 '15 at 21:44

It seems that the problem is how are defined lengths \mywidth, \firstwidth and \secondwidth. If insted of \def\mywidth{2cm} etc use definitions:

\newlength\mywidth\setlength\mywidth{2cm}

\newlength\firstwidth
\setlength\firstwidth{1cm}

\newlength\secondwidth
\setlength\secondwidth{2\firstwidth}

Your example will work as you expected (of course, if I correctly understand your problem):

Complete MWE is:

\documentclass[tikz,border=5mm]{standalone}
    \usepackage{graphicx}

\begin{document}
\newlength\mywidth\setlength\mywidth{2cm}

\newlength\firstwidth
\setlength\firstwidth{1cm}

\newlength\secondwidth
\setlength\secondwidth{2\firstwidth}

\tikz\node[circle,draw,minimum size=1.2\mywidth,
           text=white,
           path picture={
               \node at (path picture bounding box.center){
                   \includegraphics[width=1.2\mywidth]{example-image-a}
               };
           }]{see};

\tikz\node[circle,draw,minimum size=\firstwidth,
           text=white,
           path picture={
               \node at (path picture bounding box.center){
                   \includegraphics[width=\firstwidth]{example-image-b}
               };
           }]{see};

\tikz\node[circle,draw,minimum size=\firstwidth,
           text=white,
           path picture={
               \node at (path picture bounding box.center){
                   \includegraphics[width=0.5\secondwidth]{example-image-c}
               };
           }]{see};
\end{document}