code from class, 2013-11-20

class-code-2013-11-20.rkt

(require rsound)
(require 2htdp/image)
(require 2htdp/universe)

(define (s sec) (* sec 44100))
(define samp (rs-read "/tmp/waaoow-chorus.wav"))


;; a world is (make-world nat frames)
(define-struct world (ctr next-play-time))

;; the pstream for playing
(define ps (make-pstream))
;; queue on ps:
(define (psq sound t)
  (pstream-queue ps sound t))
;; do two things
(define (both a b)
  b)

;; play a quarter-second
;; world -> world
(define (play-chunk w)
  (local
    [(define ctr (world-ctr w))]
    (cond [(time-to-play? w (pstream-current-frame ps))
           (both (psq (clip samp
                            (s (/ ctr 4))
                            (s (/ (add1 ctr) 4)))
                      (world-next-play-time w))
                 (world-bump-timer w))]
          [else w])))

(define LEAD-TIME (round (s 1/10)))
;; is it time to play, yet?
;; world frame -> boolean
(define (time-to-play? w current-time)
  (< (- (world-next-play-time w) LEAD-TIME) current-time))

(check-expect (time-to-play? (make-world 234 11025) 11020)
              true)
(check-expect (time-to-play? (make-world 234 11025) 3020)
              false)

(define SUBTIMER-INCREMENT (round (s 1/4)))
;; increase the next-time-to-play by 1/4 second
(define (world-bump-timer w)
  (make-world (add1 (world-ctr w))
              (+ SUBTIMER-INCREMENT
                 (world-next-play-time w))))

(check-expect (world-bump-timer (make-world 234 1234))
               (make-world 235 (+ SUBTIMER-INCREMENT 1234)))

;; should play fifth 1/4-sec of song
;(play-chunk (make-world 5))

;; draw the world
;; world -> image
(define (draw-world w)
  (rectangle 100 100 "solid" "lightgray"))

(big-bang (make-world 0 0)
          [on-tick play-chunk]
          [to-draw draw-world])