anchor.diff:                                                    (- (bounding-rectangle-max-x (sheet-region scrollee))
                                                        (bounding-rectangle-width (sheet-region viewport)))
                                                     (bounding-rectangle-min-x (sheet-region scrollee)))
  -              (scroll-bar-thumb-size hscrollbar) (bounding-rectangle-width (sheet-region viewport))))
  +              (scroll-bar-thumb-size hscrollbar) (bounding-rectangle-width (sheet-region viewport))
  +              (gadget-value hscrollbar :invoke-callback nil)
  +              (- (nth-value 0 (transform-position (sheet-transformation scrollee) 0 0)))
  +              ))
         ;;
         (when vscrollbar
           (setf (gadget-min-value vscrollbar)      (bounding-rectangle-min-y (sheet-region scrollee))
  
positive.code: ;;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  ;;; Boston, MA  02111-1307  USA.
  
  ;;; $Id: panes.lisp,v 1.86 2002/06/26 02:11:29 gilbert Exp $
  
  (in-package :CLIM-INTERNALS)
  
  
negative.code: (defclass viewport-pane (single-child-composite-pane) ())
  
  (defmethod allocate-space ((pane viewport-pane) width height)
    (with-slots (hscrollbar vscrollbar) (sheet-parent pane)
      (move-and-resize-sheet (first (sheet-children pane))
                             (if hscrollbar (- (gadget-value hscrollbar)) 0)
                             (if vscrollbar (- (gadget-value vscrollbar)) 0)
                             (max (space-requirement-width (compose-space (first (sheet-children pane))))
                                  width)
                             (max (space-requirement-height (compose-space (first (sheet-children pane))))
                                  height)) ))
  
  ;;;;
  ;;;; SCROLLER-PANE
  