regular-time.lisp

(defpackage :o (:use :cl :bricabrac.sdl2.event-loop :sdl2))
(in-package :o)

(defgeneric handle-event (state event type)
  (:method (state event type))
  (:method (state event (type (eql :quit)))
    (throw :quit :quit)))

(defun clock-ms ()
  (round (* (osicat:get-monotonic-time) 1000)))

(defgeneric update (state dt)
  (:method ((state number) dt)
    (mod (+ state (/ dt 1000)) #.(* 2 pi))))

(defgeneric display-on-window (state win)
  (:method (state win)
    (gl:clear-color 0.0 0.0 (+ 0.5 (/ (sin state) 3)) 1.0)
    (gl:clear :color-buffer)
    (gl-swap-window win)))

(defun start (state &optional (width 200) (height 200) (regular-dt 10))
  (with-captured-bindings (rebind *standard-output*)
    (with-everything (:window (w :w width :h height) :gl g)
      (rebind
       (let* ((last-tick (clock-ms)) (dt 0))
         (declare (type fixnum last-tick dt))
         (catch :quit
           (do-events (event :event-type type :method :wait :timeout 30)
             (handle-event state event type)
             (let ((now (clock-ms)))
               (incf dt (- now last-tick))
               (setf last-tick now))
             (multiple-value-bind (parts rest) (floor dt regular-dt)
               (dotimes (i parts)
                 (decf dt regular-dt)
                 (setf state (update state regular-dt)))
               (finish-output)
               (print (setf dt rest))
               (when (plusp parts)
                 (display-on-window state w))))))))))