(use random-bsd)
(use srfi-1)

(define (mk-grid n m )
	(let loop ((j 0) (ls '()))
		(if (= j m) ls
			(loop (+ j 1) (append ls (list
				(let loopi ((i 0) (lsi '()))
					(if (= i n) lsi
						(loopi (+ i 1) (cons (list (- (random-real) 0.5)  (- (random-real) 0.5))
									   lsi
						))))))
					))))

(define (dot2 v w)
	(+ (* (car v) (car w)) (* (cadr v) (cadr w))))

(define old-floor floor)
(define old-ceiling ceiling)
(define (floor x)
	(inexact->exact (old-floor x)))
(define (ceiling x)
	(inexact->exact (old-ceiling x)))



(define (ingrid x y grid)
	(define (ease d)
		(- (* 3 (* d d)) (* 2 (* d d))))
	(let* ((x0 (- (floor x) x))
		   (x1 (- x (ceiling x)))
		   (y0 (- (floor y) y))
		   (y1 (- y (ceiling y))))
		   (let* (
				(d0 (dot2 (list x0 y0) (list-ref (list-ref grid (floor x)) (floor y))))
				(d1 (dot2 (list x0 y1) (list-ref (list-ref grid (floor x)) (ceiling y))))
				(d2 (dot2 (list x1 y0) (list-ref (list-ref grid (ceiling x)) (floor y))))
				(d3 (dot2 (list x1 y1) (list-ref (list-ref grid (ceiling x)) (ceiling y)))))
					(+ (/ (+ d0 (ease (- d0 d1))) 2.0) 
					   (/ (+ d2 (ease (- d2 d3))) 2.0)))))

(define gr (mk-grid 4 4))
(print (map (lambda (x) (let ((rx (+ 2.0 (/ x 50.0)))) (ingrid rx rx gr))) (iota 50)))