\begin{pspicture*}(-3,-3)(4.5,5)
\psset{lightsrc=10 -20 50,viewpoint=10 -10 10,Decran=20}
\defFunction{G}(t)
   {t}
   {t dup mul .25 mul}
   {-2}
\psSolid[object=cylindre,
   r=1, h=1](-2,3,0)
\psSolid[object=cylindre,
   range=-2 2, 
   h=3,
   function=G,
   axe=0 0 1, %% valeur par défaut
   ngrid=3 8]
\end{pspicture*}