# Transparency group and decoration markings

How can I set the transparency so that the arrow belongs to the same transparency group as the path?

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}
\tikzset{%
> = stealth,
arrow over path/.style = {%
decoration = {%
markings,
mark = at position .5 with {\arrow {>};}
},
postaction = decorate
}
}
\draw[arrow over path, semitransparent] (0,0) -- (1,1);
\end{tikzpicture}
\end{document}

• I don't think this can be done easily within a path (but I could be wrong). Surrounding the \draw command with \begin{scope}[opacity=.5,transparency group] and \end{scope} should work (provided the back-end driver supports it). – Mark Wibrow May 1 '13 at 13:38
• ...and remove the semitransparent key from the \draw command. – Mark Wibrow May 1 '13 at 13:39

As requested, the comment becomes an answer:

This cannot be done currently within a path as far as I can tell. But, a transparency group can be used (provided the back-end driver supports it). Note, that the transparency is specified in the surrounding scope not the path:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}
\tikzset{%
> = stealth,
arrow over path/.style = {%
decoration = {%
markings,
mark = at position .5 with {\arrow {>};}
},
postaction = decorate
}
}
\begin{scope}[opacity=.5, transparency group]
\draw [arrow over path] (0,0) -- (1,1);
\end{scope}
\end{tikzpicture}
\end{document}