anchor.diff:              call plxormod(.false., st)
               call plgetcursor(gin)
               call plxormod(.true., st)
  -            
  -            if (gin%button .eq. 1) then 
  +
  +            if (gin%button .eq. 1) then
                  xxi = gin%wX
                  yyi = gin%wY
                  if (start) then
   !C                clear previous rectangle
                     call plline(sx, sy)
                  endif
  -               
  +
                  start = .false.
  -               
  +
                  sx(1) = xxi
                  sy(1) = yyi
                  sx(5) = xxi
                  sy(5) = yyi
               endif
  -            
  +
               if (iand(gin%state,Z'100').ne.0) then
                  xxe = gin%wX
                  yye = gin%wY
  
positive.code:            height_r, 0._plflt, 0._plflt, img_min + img_max * 0.25_plflt, &
             img_max - img_max * 0.25_plflt)
  
  !     Draw a distorted version of the original image, showing its 
  !     full dynamic range.
        call plenv(0._plflt, width_r, 0._plflt, height_r, 1, -1)
        call pllab("", "", "Distorted image example")
  
negative.code:                   call plline(sx, sy)
                 endif
                 start = .true.
  
                 sx(3) = xxe
                 sy(3) = yye
                 sx(2) = xxe
  