%N grclpl %F $MIR/src/grclpl.f
%D Clip line against clipping rectangle
%B
      SUBROUTINE GRCLPL (X0,Y0,X1,Y1,VIS)

 GRPCKG (internal routine): Change the end-points of the line (X0,Y0)
 (X1,Y1) to clip the line at the window boundary.  The algorithm is
 that of Cohen and Sutherland (ref: Newman & Sproull).

 Arguments:

 X0, Y0 (input/output, real): device coordinates of starting point
       of line.
 X1, Y1 (input/output, real): device coordinates of end point of line.
 VIS (output, logical): .TRUE. if line lies wholly or partially
       within the clipping rectangle; .FALSE. if it lies entirely
       outside the rectangle.
