anchor.diff:  (defconstant +pixie-slider-thumb-half-height+ 17)
   (defconstant +pixie-slider-thumb-height+      34)
   (defconstant +pixie-slider-thumb-half-width+   8)
  +
   
   (defclass pixie-slider-pane (pixie-gadget draggable-arming-mixin slider-pane)
     ((dragging
  
positive.code:   (dragging
      :initform nil)))
  
  (defmethod compose-space ((gadget pixie-push-button-pane) &key width height)
    (declare (ignore width height))
    (space-requirement+* (space-requirement+* (compose-label-space gadget)
  
negative.code:                      (x1     (+ x1 2))
                       (x2     (- x2 3)))
                  (draw-line* pane x1 y1 x2 y1       :ink +gray58+)
                  (draw-line* pane x1 y2 x2 y2 :ink +white+)
                  (draw-line* pane x2 y1 x2 y2 :ink +white+)))))))))
  
  ; Scrollbar
  
  