Add drawing example.

draw.rkt

@@ -0,0 +1,47 @@
+;; Copyright 2019 Edward L. Platt <elplatt@alum.mit.edu
+;;
+;; TODO: add comments
+
+#lang racket
+
+(require racket/draw)
+(require racket/gui)
+(require "sylvester.rkt")
+(require "network.rkt")
+
+(define (draw-sylvester m w h margin)
+  (define target (make-bitmap w h))
+  (define dc (new bitmap-dc% [bitmap target]))
+  (let ([edges (sylvester-undirected-edges m)]
+        [nodes (sylvester-nodes m)])
+    (for ([e edges])
+      (draw-edge m e dc (- (/ w 2) margin) margin))
+    (for ([v nodes])
+      (draw-node m v dc (- (/ w 2) margin) margin)))
+  (make-object image-snip% target))
+
+(define (draw-edge m edge dc r margin)
+  (let* ([v (sylvester-radix-value (first edge))]
+         [w (sylvester-radix-value (second edge))])
+    (send dc set-pen "gray" 2 'solid)
+    (send dc draw-line
+      (node-x v m r margin) (node-y v m r margin)
+      (node-x w m r margin) (node-y w m r margin))))
+
+(define (draw-node m v dc r margin)
+  (let ([v (sylvester-radix-value v)])
+    (send dc set-pen "black" 2 'solid)
+    (send dc draw-arc
+          (- (node-x v m r margin) 4) (- (node-y v m r margin) 4)
+          8 8 0 (* 2 pi))))
+
+(define (node-x v m r margin)
+  (let ([vtheta (* 2 pi (/ v (- (sylvester m) 1)))])
+    (+ r margin (* r (cos vtheta)))))
+
+(define (node-y v m r margin)
+  (let ([vtheta (* 2 pi (/ v (- (sylvester m) 1)))])
+    (+ r margin (* r (sin vtheta)))))
+
+(draw-sylvester 3 320 320 10)
+