anchor.diff:  
   
   (defmethod init-snake ((thesnake snake))
  +  ;; Spawn fruit
  +  (setf *fruit-position*
  +	(make-vec2 :x (* 3 (/ *window-width* 4.0))
  +		   :y (/ *window-height* 16.0)))
  +  ;; Spawn first pieces
     (loop for x from 0 to *snake-init-num-pieces*
        do (push (make-vec2 :x (- (/ *window-width* 2.0)
   			       (* *snake-piece-size* x))
  
positive.code: (defparameter *fps-message-interval* 2000)
  (defparameter *fps* 0)
  
  
  
  ;; Snake piece size
  (defvar *snake-piece-size* 20)
  (defvar *snake-piece-half-size*
    (/ *snake-piece-size* 2.0))
  ;; @ 60hz, the snake should walk:
  ;; - Easiest Mode: 1 piece per second
  ;; - Easy Mode: 5 pieces per second
  ;; - Medium Mode: 10 pieces per second
  ;; - Hard Mode: 25 pieces per second
  ;; - Hardest Mode: 50 pieces per second
  (defparameter *snake-speed* 10)
  ;; Starting number of snake pieces
  (defparameter *snake-init-num-pieces* 3)
  ;; Update interval: speed-related.
  ;; Calculated before each frame.
  (defparameter *snake-update-interval* 0)
  
negative.code:    (spd :initform 5.0 :accessor spd) ;; pixels on current frame
     (piece-list
      :initform nil
      :accessor piece-list)
     (fruit-list
      :initform nil
      :accessor fruit-list)))
  
  (defgeneric init-snake (snake)
    (:documentation "Initializes an object on screen."))
  