[texhax] pstricks, or postscript, question

[Herbert Voss]

Zbigniew Nitecki schrieb:
> Is there a way to create a macro which can be used inside a pspicture 
> environment which calls pstricks macros but calculates some parameters 
> from its arguments?
> 
> I am trying to create a macro to draw a figure which includes an 
> elliptic arc whose beginning and ending angles are computed from the 
> arguments of the macro.  But it seems I cannot do something like
>     \ellipticarc(0,0)(0.5,1){180 45 sub}{180 45 add}
> (never mind substituting #1 or #2 for the "45" above)---I get an error 
> message:
>     bad number: '180 45 sub' . 0 substituted.
> 
> Is there a way in postscript to name a number, compute its value, and 
> then use it as a parameter
> in a drawing command?

\listfiles
\documentclass{article}
\usepackage{pstricks}
\makeatletter
\def\psellipticarc at iv(#1)(#2)#3#4{%
   \begin at OpenObj
   \pst at getcoor{#1}\pst at tempa
   \pst at getcoor{#2}\pst at tempb
   \def\pst at tempc{#3 }% read verbatim
   \def\pst at tempd{#4 }% read verbatim
   \addto at pscode{\psellipticarc at definearg \psellipticarc at draw}%
   \showpointsfalse
   \end at OpenObj%
}
\makeatother
\SpecialCoor

\begin{document}
\begin{pspicture}[showgrid=true](-1,-1)(1,1)

\psellipticarc(0,0)(0.5,1){180 45 sub}{180 45 add}

\end{pspicture}
\end{document}


Herbert