anchor.diff:  (defparameter *cell-width* 15)
   (defparameter *cell-height* 14)
   (defparameter *cell-row* 0)
  -
  -(defparameter *frame-rate* 20)
  +(defparameter *number-of-frames* 15)
  +(defparameter *frame-rate* 60)
   (defparameter *screen-width* 500)
   (defparameter *screen-height* 500)
   (defparameter *bg-color* sdl:*black*)
  
positive.code: 		  :color-key (sdl:color :r 255 :b 255)))
  	   (background (when *background-image-filename*
  			 (sdl-image:load-image (namestring 
  						(merge-pathnames *background-image-filename*))))))
       (sdl:with-events ()
         (:quit-event () (prog1 t
  			 (sdl:free image)))
  
negative.code: 		  (sdl:draw-surface background)
  	      (sdl:clear-display *bg-color*))
  	      (sdl:set-cell (sdl:rectangle 
  			     :x (* current-cell *cell-width*) 
  			     :y (* *cell-row* *cell-height*)
  			     :w *cell-width*
  			     :h *cell-height*)
  			    :surface image)
  	      (sdl:draw-surface-at-* image (/ *screen-width* 2) (/ *screen-height* 2))
  	      (if (< (+ *pause-between-loops* *number-of-frames*) current-cell)
  		  (setf current-cell 0)
  		  (incf current-cell))
  	      (sdl:update-display)
  	      (when (not *running*)
  		(sdl:push-quit-event)))))))
  