anchor.diff:     (delta-time :initform 0)
      (damping :initform 0)
      (num-bodies :initform 0)
  -   (p :initform 0))
  +   (p :initform 0)
  +   (start-event :initform nil)
  +   (stop-event :initform nil))
     (:default-initargs :width 640 :height 480 :pos-x 100 :pos-y 100
                        :mode '(:double :rgb) :title "nbody"))
   
  
positive.code:         (delta-time 0.016)
          (damping 1.0)
          (p 256))
      (with-cuda-context (dev-id)
        (with-memory-blocks ((new-pos 'float4 num-bodies)
                             (old-pos 'float4 num-bodies)
                             (vel 'float4 num-bodies))
          (reset old-pos vel cluster-scale velocity-scale num-bodies)
          (memcpy-host-to-device old-pos vel)
          (let ((window (make-instance 'nbody-window)))
            (setf (slot-value window 'new-pos) new-pos)
            (setf (slot-value window 'old-pos) old-pos)
            (setf (slot-value window 'vel) vel)
            (setf (slot-value window 'delta-time) delta-time)
            (setf (slot-value window 'damping) damping)
            (setf (slot-value window 'num-bodies) num-bodies)
            (setf (slot-value window 'p) p)
            (glut:display-window window))))))
  
negative.code:   ;; compute-perf-stats
    ;; show-log
    )
  |#
  
  (defclass nbody-window (glut:window)
    ((new-pos :initform nil)
  