(use-modules (graphgif)
	     (srfi srfi-1))

(define red (create-color 1 0 0))

(define my-graph
  `(((10 . 10) (1))
    ((30 . 20) () ,red)))

(define more-complex-graph
  `(((10 . 10) ()) 
    ((40 . 10) (0))
    ((25 . 25) (0 1))
    ((10 . 40) (0 2 4))
    ((40 . 40) (1 2 3))))

(define (idx->x i w)
  (modulo i w))

(define (idx->y i w)
  (quotient i w))

(define (xy->idx x y w)
  (+ (* y w) x))

(define (idx->edges i w)
  (filter-map
   (lambda (offset)
     (let* ([x (idx->x i w)]
	    [y (idx->y i w)]
	    [ox (+ x (car offset))]
	    [oy (+ y (cdr offset))])
       (and
	(not (negative? ox))
	(not (negative? oy))
	(< ox w)
	(xy->idx ox oy w))))
   ;; Auto-connect these directions if legal indices
   '(( 0 . -1)
     (-1 .  0)
     (-1 . -1)
     (+1 . -1))))

(define (generate-web w h)
  (define (make-node i)
    (list
     (cons (+ (* 30 (idx->x i w)) 10)
	   (+ (* 30 (idx->y i w)) 10))
     (idx->edges i w)))
  (let loop ([i 0]
	     [lst '()])
    (if (>= i (* w h))
	(reverse lst)
	(loop (1+ i) (cons (make-node i) lst)))))

(write-graph-to-file (generate-web 10 10) "graph.gif")