(defparameter *screen-width* 640)
(defparameter *screen-height* 480)
(defvar *red* 0)

(defun draw-button (r x y)
  (sdl2:set-render-draw-color r 100 100 100 0)
  (sdl2:render-clear r)
  (sdl2:set-render-draw-color r *red* 0 *red* 0)
  (setf *red* (mod (+ *red* 1) 255))
  (sdl2:render-fill-rect r (sdl2:make-rect x y *red* *red*))
  (sdl2:delay 5))

(defun main ()
  (sdl2:with-init (:everything)
    (sdl2:with-window (window :title "SDL2 Window"
                  :w *screen-width* :h *screen-height*
                  :flags '(:shown))
      (sdl2:hide-window window)
      (sdl2:show-window window)
      (sdl2:raise-window window)
      (sdl2:with-renderer (r window)
    (sdl2:with-event-loop (:method :poll)
      (:idle ()
         (draw-button r 0 50)
         (sdl2:render-present r))
      (:quit () t))))))