anchor.diff:             "}                                                                      "))
   
   (let ((m-pos           nil)
  -      (m-num-particles 0  )
  -      ;(m-point-size    1.0)
  +      (m-num-particles 0)
  +      (m-point-size    1.0)
         (m-sprite-size   2.0)
         (m-vertex-shader nil)
         (m-pixel-shader  nil)
  
positive.code:   ; (particle-renderer-set-spirte-size ...)
    (memcpy-device-to-host pos)
    (particle-renderer-set-positions pos num-bodies)
    (particle-renderer-display))
  
  
  ;;;
  
negative.code:     (declare (ignore pbo num-particles))
      (not-implemented))
    
    (defun particle-renderer-display (mode)
      (ecase mode
        (:particle-points
          (gl:color 1.0 1.0 1.0)
          (gl:point-size m-point-size)
          (draw-points))
        (:particle-sprites
          (gl:enable :point-sprite)
          (gl:tex-env :point-sprite :coord-replace :true)
          (gl:enable :vertex-program-point-size-nv)
          (gl:point-size m-sprite-size)
          (gl:blend-func :src-alpha :one)
          (gl:enable :blend)
          (gl:depth-mask :false)
          
          (gl:use-program m-program)
          (gl:uniformi (gl:get-uniform-location m-program "splatTexture") 0)
          
          (gl:active-texture :texture0-arb)
          (gl:bind-texture :texture-2d m-texture)
          
          (gl:color 1.0 1.0 1.0)
          (gl:secondary-color (aref m-base-color 0) (aref m-base-color 1) (aref m-base-color 2))
          
          (draw-points)
          
          (gl:use-program 0)
          
          (gl:disable :point-sprite-arb)
          (gl:disable :blend)
          (gl:depth-mask :true))))
    
    (defun particle-renderer-set-point-size (size)
      (declare (ignore size))
  