(require 'lispbuilder-sdl)

(defun game (&optional (width 320) (height 240) (speed 1))
  (let ((v-coord (/ height 2)))
    (sdl:with-init ()
    (sdl:window width height :title-caption "My game")
    (setf (sdl:frame-rate) 60)
    (sdl:with-events ()
      (:quit-event () t)
      (:idle ()
        (sdl:clear-display sdl:*white*)
        (setf speed (if (or (< v-coord 10) (> v-coord (- height 10)))
          (- speed)
              speed))
        (sdl:draw-box (sdl:rectangle-from-midpoint-*
          (/ width 2) (incf v-coord speed) 20 20) :color sdl:*red*)
        (sdl:update-display))))))

(defparameter *decoy* (pairlis '(h-coord v-coord h-speed v-speed) '(120 160 2 2)))

(:idle ()
  (acons 'h-coord (+ (cdr (assoc 'h-coord *decoy*)) (cdr (assoc 'h-speed *decoy*))) *decoy*)
  (acons 'v-coord (+ (cdr (assoc 'v-coord *decoy*)) (cdr (assoc 'v-speed *decoy*))) *decoy*)
  (sdl:draw-box (sdl:rectangle-from-midpoint-*
      (cdr (assoc 'h-coord *decoy*)) (cdr (assoc 'v-coord *decoy*)) 20 20)
      :color sdl:*red*)

(defun game (&optional (width 320) (height 240) (speed 2))
  (let ((decoy (pairlis '(h-coord v-coord h-speed v-speed)
                        '((/ width 2) (/ height 2) speed speed))))
  (sdl:with-init ()
    (sdl:window width height :title-caption "My game")
    (setf (sdl:frame-rate) 60)
    (sdl:with-events ()
      (:quit-event () t)
      (:key-down-event (:key key)
        (when (sdl:key= key :sdl-key-escape) (sdl:push-quit-event)))
      (:idle ()
        (acons 'h-coord (+ (cdr (assoc 'h-coord decoy))
               (cdr (assoc 'h-speed decoy))) decoy)
        (acons 'v-coord (+ (cdr (assoc 'v-coord *decoy*))
               (cdr (assoc 'v-speed decoy))) decoy)
      (sdl:clear-display sdl:*white*
        :surface (sdl:draw-surface (sdl:load-image *bg*)))
      (sdl:draw-box (sdl:rectangle-from-midpoint-*
        (cdr (assoc 'h-coord decoy)) (cdr (assoc 'v-coord decoy)) 20 20)
        :color sdl:*red*)
      (sdl:update-display))))))