bundles/org.eclipse.draw2d/src/org/eclipse/draw2d/graph/GraphUtilities.java

/*******************************************************************************
 * Copyright (c) 2003, 2010 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.draw2d.graph;

/**
 * Some utility methods for graphs.
 * 
 * @author Eric Bordeau
 * @since 2.1.2
 */
class GraphUtilities {

	static Subgraph getCommonAncestor(Node left, Node right) {
		Subgraph parent;
		if (right instanceof Subgraph)
			parent = (Subgraph) right;
		else
			parent = right.getParent();
		while (parent != null) {
			if (parent.isNested(left))
				return parent;
			parent = parent.getParent();
		}
		return null;
	}

	/**
	 * Returns <code>true</code> if the given graph contains at least one cycle.
	 * 
	 * @param graph
	 *            the graph to test
	 * @return whether the graph is cyclic
	 */
	public static boolean isCyclic(DirectedGraph graph) {
		return isCyclic(new NodeList(graph.nodes));
	}

	/**
	 * Recursively removes leaf nodes from the list until there are no nodes
	 * remaining (acyclic) or there are no leaf nodes but the list is not empty
	 * (cyclic), then returns the result.
	 * 
	 * @param nodes
	 *            the list of nodes to test
	 * @return whether the graph is cyclic
	 */
	public static boolean isCyclic(NodeList nodes) {
		if (nodes.isEmpty())
			return false;
		int size = nodes.size();
		// remove all the leaf nodes from the graph
		for (int i = 0; i < nodes.size(); i++) {
			Node node = nodes.getNode(i);
			if (node.outgoing == null || node.outgoing.isEmpty()) { // this is a
																	// leaf node
				nodes.remove(node);
				for (int j = 0; j < node.incoming.size(); j++) {
					Edge e = node.incoming.getEdge(j);
					e.source.outgoing.remove(e);
				}
			}
		}
		// if no nodes were removed, that means there are no leaf nodes and the
		// graph is cyclic
		if (nodes.size() == size)
			return true;
		// leaf nodes were removed, so recursively call this method with the new
		// list
		return isCyclic(nodes);
	}

	/**
	 * Counts the number of edge crossings in a DirectedGraph
	 * 
	 * @param graph
	 *            the graph whose crossed edges are counted
	 * @return the number of edge crossings in the graph
	 */
	public static int numberOfCrossingsInGraph(DirectedGraph graph) {
		int crossings = 0;
		for (int i = 0; i < graph.ranks.size(); i++) {
			Rank rank = graph.ranks.getRank(i);
			crossings += numberOfCrossingsInRank(rank);
		}
		return crossings;
	}

	/**
	 * Counts the number of edge crossings in a Rank
	 * 
	 * @param rank
	 *            the rank whose crossed edges are counted
	 * @return the number of edge crossings in the rank
	 */
	public static int numberOfCrossingsInRank(Rank rank) {
		int crossings = 0;
		for (int i = 0; i < rank.size() - 1; i++) {
			Node currentNode = rank.getNode(i);
			Node nextNode;
			for (int j = i + 1; j < rank.size(); j++) {
				nextNode = rank.getNode(j);
				EdgeList currentOutgoing = currentNode.outgoing;
				EdgeList nextOutgoing = nextNode.outgoing;
				for (int k = 0; k < currentOutgoing.size(); k++) {
					Edge currentEdge = currentOutgoing.getEdge(k);
					for (int l = 0; l < nextOutgoing.size(); l++) {
						if (nextOutgoing.getEdge(l).getIndexForRank(
								currentNode.rank + 1) < currentEdge
								.getIndexForRank(currentNode.rank + 1))
							crossings++;
					}
				}
			}
		}
		return crossings;
	}

	private static NodeList search(Node node, NodeList list) {
		if (node.flag)
			return list;
		node.flag = true;
		list.add(node);
		for (int i = 0; i < node.outgoing.size(); i++)
			search(node.outgoing.getEdge(i).target, list);
		return list;
	}

	/**
	 * Returns <code>true</code> if adding an edge between the 2 given nodes
	 * will introduce a cycle in the containing graph.
	 * 
	 * @param source
	 *            the potential source node
	 * @param target
	 *            the potential target node
	 * @return whether an edge between the 2 given nodes will introduce a cycle
	 */
	public static boolean willCauseCycle(Node source, Node target) {
		NodeList nodes = search(target, new NodeList());
		nodes.resetFlags();
		return nodes.contains(source);
	}

	static boolean isConstrained(Node left, Node right) {
		Subgraph common = left.getParent();
		while (common != null && !common.isNested(right)) {
			left = left.getParent();
			common = left.getParent();
		}
		while (right.getParent() != common)
			right = right.getParent();
		return (left.rowOrder != -1 && right.rowOrder != -1)
				&& left.rowOrder != right.rowOrder;
	}

}