[Tex/LaTex] Transparent background spanning several tikzpictures

tikz-pgfwatermark

I am trying to display a "forbidden sign" in the background of
two tikzpictures (much like some kind of watermark).
However, in the following MWE the "forbidden sign" is cut-off at some
seemingly arbitrary horizontal line.

\documentclass{scrartcl}

\usepackage{tikz}
\usetikzlibrary{backgrounds,shapes}

\begin{document}
\noindent
  \begin{tikzpicture}
    \draw[green] (0.0, -5.0) rectangle (10.0, 0.0);
  \end{tikzpicture}\\
  \begin{tikzpicture}
    \draw[blue] (0.0, -5.0) rectangle (10.0, 0.0);
    \begin{pgfonlayer}{background}
      \begin{scope}[opacity=0.5,transparency group,overlay]
        \draw node[forbidden sign,
                   minimum size=5cm,
                   line width=2ex,
                   draw=red,
                   fill=white] at (5.0,0.0) {Test};
      \end{scope}
    \end{pgfonlayer}
  \end{tikzpicture}
\end{document}

Do you have any idea how I can fix this behaviour?

Best Answer

It seems difficult to use overlay with transparency group

\documentclass{scrartcl}
\usepackage{tikz}
\usetikzlibrary{backgrounds,shapes}
\pgfdeclarelayer{myback}    
\pgfsetlayers{myback,main}
\newsavebox{\mybox}   
\begin{document}
\parindent=0pt 

\savebox{\mybox}{%
\begin{tikzpicture}[transparency group,opacity=.5]
        \node[forbidden sign,
              minimum size=5cm,
              line width=2ex,
              draw=red,
              fill=white]  {};
\end{tikzpicture}} 

  \begin{tikzpicture}
    \draw[green] (0.0, -5.0) rectangle (10.0, 0.0);
  \end{tikzpicture}\\ \baselineskip=0pt     
 \begin{tikzpicture}[remember picture,overlay]
    \draw[blue] (0.0, -5.0) rectangle (10.0, 0.0);
      \begin{pgfonlayer}{myback}
    \node[inner sep=0pt] (s) at (5,0){\usebox\mybox};
    \end{pgfonlayer} 
  \end{tikzpicture}

\end{document}

enter image description here

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