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<font face="Myriad Pro">Dear Alexander,<br>
<br>
try this:<br>
<br>
\makeatletter<br>
% Draw two overlapped surfaces, with computation of the mixed color for<br>
% the intersection of the surfaces<br>
% #1=first&nbsp; surface, #2=color of first&nbsp; surface,<br>
% #3=second surface, #4=color of second surface<br>
\def\ColoredOverlappedSurfaces#1#2#3#4{%<br>
&nbsp; \psset{fillstyle=solid}%<br>
&nbsp; % Decode the three components of the first RGB color<br>
&nbsp; \psset{fillcolor=#2}% % Draw first surface<br>
&nbsp; #1<br>
&nbsp; % Decode the three components of the second RGB color<br>
&nbsp; % Draw second surface<br>
&nbsp; \psclip{\psset{fillcolor=#4}#3}%<br>
&nbsp; \psset{fillcolor=#2!50!#4}%<br>
&nbsp; % Redraw overlapped surface in the mixed color<br>
&nbsp; #1%<br>
&nbsp; \endpsclip%<br>
}<br>
\makeatother<br>
<br>
<br>
Regards,<br>
<br>
Juergen<br>
</font><br>
Alexander Grahn wrote:
<blockquote cite="mid:20090610125357.GA20796@fzd.de" type="cite">
  <pre wrap="">Hi,

I wish it were possible to mix the colour of overlapping objects but,
at the same time, to prevent the background colour from being mixed in.

Consider the example below where I have a red (rgb=1 0 0) circle and a
blue (rgb=0 0 1) ellipse, overlapping each other. It would be extremely
nice to have the overlapping region to be filled with colour rgb=1 0 1
and the non-overlapping regions to be filled with fully saturated red
and blue colours.

Unfortunately, neither black nor white backgrounds give the desired
result.

Is there a way to achieve this in the final ps2pdf generated PDF?

Thanks for your suggestions!

Regards,
Alexander

\documentclass{article}
\usepackage{pstricks}

\def\ColoredOverlappedSurfaces#1#2#3#4{%
  \psset{fillstyle=solid,opacity=0.5}%
  \psset{fillcolor=#2}#1
  \psset{fillcolor=#4}#3}

\pagestyle{empty}

\begin{document}

\psset{unit=2}
\psframebox*[fillcolor=black,fillstyle=solid]{%
\begin{pspicture}(-2,-2)(2,2)
\rput(0,0){%
  \ColoredOverlappedSurfaces{\pscircle{1}}{red}{\psellipse(0.3,-0.7)(1.5,1)}{blue}}
\end{pspicture}}

\begin{pspicture}(-2,-2)(2,2)
\rput(0,0){%
  \ColoredOverlappedSurfaces{\pscircle{1}}{red}{\psellipse(0.3,-0.7)(1.5,1)}{blue}}
\end{pspicture}
\end{document}
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  </pre>
</blockquote>
<br>
<pre class="moz-signature" cols="65">-- 
 J&uuml;rgen Gilg
 Austr. 59
 70376 Stuttgart
-------------------------------------
 Tel       0711.59 27 88
 e-Mail    <a class="moz-txt-link-abbreviated" href="mailto:gilg@acrotex.net">gilg@acrotex.net</a>

</pre>
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