[pstricks] mixing colours of overlapping objects while disregarding paper background colour

[Alexander Grahn]

Thanks Juergen, it's perfect!

On Wed, Jun 10, 2009 at 03:40:50PM +0200, Juergen Gilg wrote:
> \makeatletter
> % Draw two overlapped surfaces, with computation of the mixed color for
> % the intersection of the surfaces
> % #1=first  surface, #2=color of first  surface,
> % #3=second surface, #4=color of second surface
> \def\ColoredOverlappedSurfaces#1#2#3#4{%
>  \psset{fillstyle=solid}%
>  % Decode the three components of the first RGB color
>  \psset{fillcolor=#2}% % Draw first surface
>  #1
>  % Decode the three components of the second RGB color
>  % Draw second surface
>  \psclip{\psset{fillcolor=#4}#3}%
>  \psset{fillcolor=#2!50!#4}%
>  % Redraw overlapped surface in the mixed color
>  #1%
>  \endpsclip%
> }
> \makeatother

Now I'd like to do the same with lines. For this purpose I modified your
example (see below). However, it does not work as expected. Any Idea?

Thanks again and in advance!
Alexander

\documentclass{article}
\usepackage{pstricks}

\makeatletter
% Draw two overlapped lines, with computation of the mixed color for
% the intersection of them.
% #1=first  line, #2=color of first line,
% #3=second line, #4=color of second line
\def\ColoredOverlappedLines#1#2#3#4{%
 % Decode the three components of the first RGB color
 \psset{linecolor=#2}% % Draw first line
 #1
 % Decode the three components of the second RGB color
 % Draw second line
 \psclip{\psset{linecolor=#4}#3}%
 \psset{linecolor=#2!50!#4}%
 % Redraw overlapping line segment in the mixed color
 #1%
 \endpsclip%
}
\makeatother

\pagestyle{empty}

\begin{document}

\psset{unit=2}
\psset{linewidth=5pt}
\psframebox*[fillcolor=black,fillstyle=solid]{%
\begin{pspicture}(-2,-2)(2,2)
\rput(0,0){%
  \ColoredOverlappedLines{\qline(-2,-2)(2,2)}{red}{\qline(-2,2)(2,-2)}{blue}}
\end{pspicture}}

\begin{pspicture}(-2,-2)(2,2)
\rput(0,0){%
  \ColoredOverlappedLines{\qline(-2,-2)(2,2)}{red}{\qline(-2,2)(2,-2)}{blue}}
\end{pspicture}
\end{document}