;;
;; particles.al: create all particles at start
;;

(define *particles* '())
(define *num-particles* 10)

(define (randR low high) (+ low (* (rand) (- high low))))

(define (make-one-particle)
  (list	(list 'pp (vec3 0 0 0))
	(list 'pv (vec3 0 0 0))
	(list 'pa (vec3 0 0 0))
	))

(define (add-particle p)
  (set! *particles* (cons p *particles*)))

(define (get-value p key)
  (list-ref (assq key p) 1))

(define (set-value p key val)
  (set-cdr! (assq key p) (list val)))

(define (update-particle p)
  (let ((pos (get-value p 'pp))
	(vel (get-value p 'pv))
	(acc (get-value p 'pa)))
    (set-value p 'pp (+ pos vel))
    (set-value p 'pv (+ vel acc))
    ))

(define (update-particles)
  (map update-particle *particles*))

(define (draw-particle p)
  (separator
    (translate (get-value p 'pp))
    (uscale .1)
    (sphere)))

(define (draw-particles)
  (map draw-particle *particles*))

(define (create-particle)
  (let (
	(p (make-one-particle))
	)
    (set-value p 'pp (vec3 0 0 0))
    (set-value p 'pv (vec3 (randR -.03 .03) (randR .08 .12) 0))
    (set-value p 'pa (vec3 0 -.005 0))
    (add-particle p)
    ))

(define (create-particles)
  (for i 1 *num-particles* 1
       (create-particle)))

(define (sim)
  (begin
    (create-particles)
    (for i 1 60 1
	 (begin
	   (world
	     (draw-particles)
	     )
	   (update-particles)
	   ))))

(sim)