anchor.diff:      (prog1
           (call-next-method)
         (unless (eql oldval newval)
  -        (#_update instance (cannon-rect instance))
  +        (with-objects ((rect (cannon-rect instance)))
  +          (#_update instance rect))
           (emit-signal instance "forceChanged(int)" newval)))))
   
   (defun cannon-rect (instance)
  
positive.code: 
  (defun paint-shot (instance painter)
    (#_setPen painter (#_NoPen "Qt"))
    (#_setBrush painter (#_new QBrush (#_black "Qt") (#_SolidPattern "Qt")))
    (#_drawRect painter (shot-rect instance)))
  
  (defun paint-cannon (instance painter)
    (#_setPen painter (#_NoPen "Qt"))
    (#_setBrush painter (#_new QBrush (#_blue "Qt") (#_SolidPattern "Qt")))
  
    (#_save painter)
    (#_translate painter 0 (#_height (#_rect instance)))
    (#_drawPie painter (#_new QRect -35 -35 70 70) 0 (* 90 16))
    (#_rotate painter (- (current-angle instance)))
    (#_drawRect painter (#_new QRect 30 -5 20 10))
    (#_restore painter))
  
  (defun paint-target (instance painter)
    (#_setPen painter (#_NoPen "Qt"))
    (#_setBrush painter (#_new QBrush (#_red "Qt") (#_SolidPattern "Qt")))
    (#_drawRect painter (target-rect instance)))
  
  (defun paint-barrier (instance painter)
    (#_setPen painter (#_new QPen (#_black "Qt")))
    (#_setBrush painter (#_new QBrush (#_blue "Qt") (#_SolidPattern "Qt")))
    (#_drawRect painter (barrier-rect instance)))
  
  (defmethod paint-event ((instance cannon-field) paint-event)
    (let ((painter (#_new QPainter instance)))
      (when (game-ended-p instance)
        (#_setPen painter (#_black "Qt"))
        (#_setFont painter (#_new QFont "Courier" 48 (#_Bold "QFont")))
        (#_drawText painter (#_rect instance) (#_AlignCenter "Qt") "Game Over"))
      (paint-cannon instance painter)
      (when (is-shooting-p instance)
  
negative.code:                   :accessor shoot-angle)
       (shoot-force :initform 0
                    :accessor shoot-force)
       (target :initform nil
               :accessor target)
       (game-ended-p :initform nil
                     :accessor game-ended-p)
       (barrel-pressed-p :initform nil
  