Description: Restrict drawing to a window area
Mapped Command: SET DRAWING AREA
FUNCTION __SetDrawArea(Pos1a,Pos1b,Pos2a,Pos2b)
   if Pos1a == NIL
      clipwin(0,0,1350,1000)
   else
      clipwin(__XdGE(Pos1b),__YdGE(Pos2a),__XdGE(Pos2b),__YdGE(Pos1a))
   endif                                         // if pos1a == nil
RETURN(Void)