SetViewPort procedure

  DECLARATION:  SetViewPort(X1, Y1, X2, Y2 : Integer; Clip : Boolean);

      PURPOSE:  Sets the current output viewport or window for graphics

         UNIT:  Graph

      REMARKS:  The upper left-hand corner are specified by (X1,Y1) and the
                the lower right-hand corner is specified by (X2,Y2).  Once
                defined, (0,0) is the upper left-hand corner of a view port.

                The boolean variable, Clip, specifies is drawings are to be
                clipped at the view port boundaries.  A call to SetViewPort
                with invalid parameters will cause GraphResult to return a
                value of -11 (grError) and the current view port settings
                will be left unchanged.

                A call to  SetViewPort(0, 0,GetMaxX, GetMaxY, True) will
                set the viewport to the entire screen.

 RESTRICTIONS:  Must first be in graphics mode.