builder.start()
	defer builder.finish()
	builder.addLegend()

	if len(g.Nodes) == 0 {
		return
	}

	// Preprocess graph to get id map and find max flat.
	nodeIDMap := make(map[*Node]int)
	hasNodelets := make(map[*Node]bool)

	maxFlat := float64(abs64(g.Nodes[0].FlatValue()))
	for i, n := range g.Nodes {
		nodeIDMap[n] = i + 1
		if float64(abs64(n.FlatValue())) > maxFlat {
			maxFlat = float64(abs64(n.FlatValue()))