Sound and Animation

In order to play a sound on a unix machine you must give a call like this:

(exec "mpg123 mysoundfile.mp3 &")

where mysoundfile.mp3 is an mp3 that you have. Note: please do not make this too large a file. (Your account cannot be too large).

If you want to animate your images you have to do it in an inconvenient, roundabout way. You must have a bunch of pictures which are frames of an animation (as in a .gif, but not embedded in it; each frame must be a separate file). Here is some cool code to animate the frames for you:

(define flicker
  (lambda (picture-list tag speed)
    (let* ((a 1)
	  (kill #f)
	  (func 
	   (lambda (f)
	     (after speed (lambda ()  
			    (set! a (remainder a (length picture-list)))
			    (set-image! tag (list-ref picture-list a))
			    (set! a (+ a 1))
			    (if (not kill)
				(f f)))))))
      (func func)
      (lambda () (set! kill #t)))))

Note: You should have no idea why this works, and that is fine. Set! should be a mystery to you and it should continue to be so. You call the function by giving it a list of paths of pictures like:
(define pic-list (list "gamesman/images/xicongreen.gif" "gamesman/images/xiconred.gif" "gamesman/images/xicongrey.gif" "gamesman/images/xiconyellow.gif")),
the tag that you want to change the picture of, and the speed which that it goes through pictures (in milliseconds).

The function call returns a procedure of no arguments that stops the animation when it is called. Here are some example interactions:

(draw-image 100 100 "gamesman/images/xiconred.gif" 'tag 'bigx1)
(define stop1 (flicker pic-list 'bigx1 100))
(draw-image 300 300 "gamesman/images/xiconred.gif" 'tag 'bigx2)
(define stop2 (flicker pic-list 'bigx2 100))
;; Now Both are animated
(stop1)
;; The first has stoped being animated.
(stop2)
;; The second is now stopped.

Remember, any and all questions are welcome on the CS3 newsgroup!

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