anchor.diff:  
   (defun theta-callback (gadget degrees)
     (declare (ignore gadget))
  -  (let ((viewer (find-pane-named *application-frame* 'viewer)))
  +  (let ((viewer (find-pane-named *application-frame* 'spectacle-pane)))
       (with-accessors ((image gadget-value)
                        (transform-parameters transform-parameters)
                        (transform transform))
  
positive.code: 
  (defun x-shear-callback (gadget shear)
    (declare (ignore gadget))
    (let ((viewer (find-pane-named *application-frame* 'viewer)))
      (with-accessors ((image gadget-value)
                       (transform-parameters transform-parameters)
                       (transform transform))
  
negative.code:     ((image-pathname 'pathname
                       :default (user-homedir-pathname)
                       :insert-default t))
    (let ((viewer (find-pane-named *application-frame* 'spectacle-pane))
          (img (read-image-file image-pathname)))
      (with-accessors ((image gadget-value)
                       (transform-parameters transform-parameters)
                       (transform transform))
          viewer
        (reset-sliders)
        (reset-transform-parameters transform-parameters)
        (setf transform nil
              image img)
        (com-zoom))))
  
  (define-spectacle-command (com-zoom :name t)
      ()
    (let ((viewer (find-pane-named *application-frame* 'spectacle-pane)))
      (let ((y-scale-slider (find-pane-named *application-frame* 'y-scale))
            (x-scale-slider (find-pane-named *application-frame* 'x-scale))
            (bounding-rectangle-height (bounding-rectangle-height viewer))
            (bounding-rectangle-width (bounding-rectangle-width viewer)))
        (with-accessors ((image gadget-value)
                         (transform-parameters transform-parameters)
                         (transform transform))
            viewer
          (when image
            (with-image-bounds (oldy oldx) image
              (let ((scale (apply #'min
  