Source PostScript (ordorig.pps)

%% syntaxe : A B ordorig
%% attention, la droite est supposee ne pas etre verticale
/ordorig {
   /dr@ite 4 array def
   dr@ite 3 3 -1 roll put
   dr@ite 2 3 -1 roll put
   dr@ite 1 3 -1 roll put
   dr@ite 0 3 -1 roll put
   dr@ite aload pop coeffdir /c@eff exch def
   dr@ite aload pop pop pop  %% xA yA
   exch                      %% yA xA 
   c@eff mul neg add
} def