;;
;; behave2.al: multiple beasts, repulse plus center attract
;;

(define *sim-length* 90)
(define *render?* #t)
(define *repulse-force* .005)
(define *attract-force* .1)
(define *num-beasts* 20)
(define *beasts* '())
(define *speed* .1)

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

(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-beast beast)
  (let ((force 0)
	(pos (get-value beast 'p))
	(change (vec3 0 0 0))
	)
	
    ; calc repulse force from other beasts
    (for i 0 (- *num-beasts* 1) 1
	 ; don't compare beast to itself
	 (if (not (eq? beast (list-ref *beasts* i)))
	     (let* ((other-beast (list-ref *beasts* i))
		    (other-pos (get-value other-beast 'p))
		    (d (distance pos other-pos))
		    (dir (normalize (- pos other-pos)))
		    (f (* *repulse-force* (/ 1 (sqr d)) dir))
		    )
	       (set! force (+ force f))
	       ))
	 )

    ; calc attract force to center
    (set! force (+ force (* *attract-force*
			    (sqr (norm pos))
			    (normalize (- pos)))))

    ; calc beast move
    (set! change (* (normalize force) (get-value beast 'speed)))
    (set-value beast 'v change)
	 
    ; set new beast position
    (set-value beast 'p (+ pos change))
    ))

(define (update-beasts)
  (map update-beast *beasts*))

(define (draw-beast beast)
  (separator
    (translate (get-value beast 'p))
    (uscale .1)
    (color 1 0 0)
    (sphere)))

(define (draw-beasts)
  (map draw-beast *beasts*))

(define (add-beast p)
  (set! *beasts* (cons p *beasts*)))

(define (make-one-beast)
  (list	(list 'p (vec3 0 0 0))
	(list 'v (vec3 0 0 0))
	(list 'speed 1)
	))

(define (create-beast)
  (let (
	(b (make-one-beast))
	)
    (set-value b 'p (vec3 (randR -1 1) (randR -1 1) 0))
    (set-value b 'v (vec3 (randR -1 1) (randR -1 1) 0))
    (set-value b 'speed *speed*)
    (add-beast b)
    ))

(define (create-beasts)
  (for i 1 *num-beasts* 1
       (create-beast)))

(define (sim)
  (begin
    (create-beasts)
    (for i 1 *sim-length* 1
	 (begin
	   (world
	     (camera "main" "orthographic" 'from (vec3 0 0 1.25))
	     (draw-beasts)
	     )

	   (if *render?*
	       (render
		'style "vector"
		'format '(320 242)
		'display-type "sgif"
		'display-name (string-append "Frames/f"
					     (number->string i)
					     ".rgb")
		))
	   
	   (update-beasts)
	   ))))

(sim)

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