anchor.diff:    (let ((viewer (find-pane-named *application-frame* 'spectacle-pane)))
       (with-accessors ((image image)
                        (transform-parameters transform-parameters)
  -                     (transform transform))
  +                     (transform transform)
  +                     (clear-background-needed-p clear-background-needed-p))
           viewer
         (let ((param 4))
           (unless (equal (elt transform-parameters param) shear)
             (setf (elt transform-parameters param) shear
  -                transform nil)
  +                transform nil
  +                clear-background-needed-p t)
             (handle-repaint viewer (or (pane-viewport-region viewer)
                                        (sheet-region viewer))))))))
   
  
positive.code:               (setf (gadget-value y-scale-slider) scale
                      (elt transform-parameters y-scale-param) scale)))
            (setf (elt transform-parameters x-scale-param) scale
                  transform nil)
            (handle-repaint viewer (or (pane-viewport-region viewer)
                                       (sheet-region viewer))))))))
  
  
negative.code:               (setf (gadget-value x-scale-slider) scale
                      (elt transform-parameters x-scale-param) scale)))
            (setf (elt transform-parameters y-scale-param) scale
                  transform nil
                  ;; FIXME! This isn't strictly needed unless we're
                  ;; resizing the image to be smaller than the screen --
                  ;; we should fix this by clearing the screen in
                  ;; handle-repaint if we're not completely drawing over
                  ;; the viewport!
                  clear-background-needed-p t)
            (handle-repaint viewer (or (pane-viewport-region viewer)
                                       (sheet-region viewer))))))))
  
  