anchor.diff:      :accessor game-quit)
      (wave
       :accessor game-wave)
  +   (background
  +    :accessor game-background)
      (sound
       :accessor game-sound)
      (enemy-missiles
  
positive.code:     :accessor level
      :initform 0)))
  
  (defclass players-left-controller (alarm)
    ((players-left
      :accessor players-left
      :initform 0)))
  
  (defclass quit-controller (actor) ())
  
  (defclass shooter (actor)
    ((bullet-class
  
negative.code:             (incf (players-left (players-left screen)))))
      (let* ((tile-names '(:forest-0 :forest-1 :forest-2 :forest-3
                           :forest-4 :forest-5 :forest-6))
             (tiles (iter (for name in tile-names)
                          (collect (make-image name))))
             (num-tiles (length tiles))
             (tile-size (size (first tiles))))
        (iter (for x from 0 below (x size) by (x tile-size))
              (iter (for y from 0 below (y size) by (y tile-size))
                    (make-instance 'tile
                                   :parent root
                                   :offset (complex x y)
                                   :veloc #c(0 1/2)
                                   :image (nth (mt19937:random num-tiles)
                                               tiles)
                                   :depth 100))))))
  