Draw large web

demo.scm

@@ -1,4 +1,5 @@
-(use-modules (graphgif))
+(use-modules (graphgif)
+	     (srfi srfi-1))
 
 (define my-graph
   `(((10 . 10) (1) ,white)
@@ -11,4 +12,41 @@
     ((10 . 40) (0 2 4) ,white)
     ((40 . 40) (1 2 3) ,white)))
 
-(write-graph-to-file more-complex-graph (cadr (command-line)))
+(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 (x y)
+     (if (or (negative? (+ (idx->x i w) x))
+	     (negative? (+ (idx->y i w) y))
+	     (>= (+ (idx->x i w) x) w))
+	 #f
+	 (xy->idx
+	  (+ (idx->x i w) x)
+	  (+ (idx->y i w) y)
+	  w)))
+   '(+0 -1 -1 +1)
+   '(-1 +0 -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)
+     white))
+  (reverse
+   (let loop ([i 0]
+	      [lst '()])
+     (if (>= i (* w h))
+	 lst
+	 (loop (1+ i) (cons (make-node i) lst))))))
+
+(write-graph-to-file (generate-web 5 5) (cadr (command-line)))