anchor.diff:  (defmethod initialize-instance :after ((w test-window) &key &allow-other-keys)
     ;; GL setup can go here; your GL context is automatically active,
     ;; and this is done in the main thread.
  +  (setf (idle-render w) t)
     (gl:viewport 0 0 800 600)
     (gl:matrix-mode :projection)
     (gl:ortho -2 2 -2 2 -2 2)
  
positive.code: (in-package :sdl2.kit.test)
  
  (defclass test-window (gl-window)
    ((rotation :initform 0.0)))
  
  ;;; All of these methods are OPTIONAL.  However, without a render
  ;;; method, your window will not look like much!
  
negative.code:     (gl:vertex 0.0 1.0)
      (gl:vertex -1.0 -1.0)
      (gl:vertex 1.0 -1.0)
      (gl:end))
    (with-slots (start-time frames) window
      (incf frames)
      (let* ((current-time (get-internal-real-time))
             (seconds (/ (- current-time start-time) internal-time-units-per-second)))
        (when (> seconds 5)
          (format t "FPS: ~A~%" (float (/ frames seconds)))
          (setf frames 0)
          (setf start-time (get-internal-real-time))))))
  
  (defmethod close-window ((window test-window))
    (format t "Bye!~%")
  