anchor.diff:      (with-accessors ((image image)
                        (transform-parameters transform-parameters)
                        (transform transform)
  -                     (lock-x-and-y-scale lock-x-and-y-scale))
  +                     (lock-x-and-y-scale lock-x-and-y-scale)
  +                     (clear-background-needed-p clear-background-needed-p))
           viewer
         (let ((y-scale-param 0)
               (x-scale-param 1))
  
positive.code:             :value 1.0d0
              :show-value-p t
              :orientation :horizontal
              :drag-callback #'x-scale-callback
              :value-changed-callback 'x-scale-callback)
     (theta :slider
            :min-value -180
  
negative.code:             :value 0.0d0
              :show-value-p t
              :orientation :horizontal
              :drag-callback 'x-shear-callback
              :value-changed-callback 'x-shear-callback)
     (reset-button :push-button
                   :label "Reset Parameters"
  