anchor.diff:  ;;;
   
   (defmethod glut:display-window :before ((w nbody-window))
  -  (gl:clear-color 0 0 0 0))
  +  (gl:clear-color 0 0 0 0)
  +  (nbody-demo-init))
   
   (defmethod glut:display ((w nbody-window))
     (with-slots (new-pos old-pos vel delta-time damping num-bodies p) w
  
positive.code: ;;; Particle Renderer
  ;;;
  
  (let ((m-pos           nil)
        (m-num-particles 0  )
        (m-point-size    1.0)
        ;(m-sprite-size   2.0)
        ;(m-vertex-shader nil)
        ;(m-pixel-shader  nil)
        ;(m-program       nil)
        ;(m-texture       nil)
        ;(m-pbo           nil)
        ;(m-vbo-color     nil)
        ;(m-base-color    nil))
        )
    
    (defun particle-renderer-set-positions (pos num-particles)
      (setf m-pos pos)
      (setf m-num-particles num-particles))
    
    (defun particle-renderer-set-base-color (color)
      (declare (ignore color))
      (not-implemented))
    
    (defun particle-renderer-set-colors (color num-particles)
      (declare (ignore color num-particles))
  
negative.code: ;;; NBodyDemo
  ;;;
  
  (defun nbody-demo-init ()
    (particle-renderer-init)
    (nbody-demo-reset-renderer))
  
  (defun nbody-demo-release ()
    (particle-renderer-release))
  
  (defun nbody-demo-reset-renderer ()
    (particle-renderer-set-base-color #(1.0 0.6 0.3 1.0)))
  
  (defun nbody-demo-update-simulation (new-pos old-pos vel delta-time damping num-bodies p)
    (integrate-nbody-system new-pos old-pos vel delta-time damping num-bodies p))
  
  