bundles/org.eclipse.draw2d/src/org/eclipse/draw2d/graph/LocalOptimizer.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;

/**
 * This graph visitor examines all adjacent pairs of nodes and determines if
 * swapping the two nodes provides improved graph aesthetics.
 * 
 * @author Daniel Lee
 * @since 2.1.2
 */
class LocalOptimizer extends GraphVisitor {

	boolean shouldSwap(Node current, Node next) {
		if (GraphUtilities.isConstrained(current, next))
			return false;
		int crossCount = 0;
		int invertedCrossCount = 0;

		EdgeList currentEdges = current.incoming;
		EdgeList nextEdges = next.incoming;
		int rank = current.rank - 1;
		int iCurrent, iNext;

		for (int i = 0; i < currentEdges.size(); i++) {
			Edge currentEdge = currentEdges.getEdge(i);
			iCurrent = currentEdge.getIndexForRank(rank);
			for (int j = 0; j < nextEdges.size(); j++) {
				iNext = nextEdges.getEdge(j).getIndexForRank(rank);
				if (iNext < iCurrent)
					crossCount++;
				else if (iNext > iCurrent)
					invertedCrossCount++;
				else {
					// edges go to the same location
					int offsetDiff = nextEdges.getEdge(j).getSourceOffset()
							- currentEdge.getSourceOffset();
					if (offsetDiff < 0)
						crossCount++;
					else if (offsetDiff > 0)
						invertedCrossCount++;
				}
			}
		}

		currentEdges = current.outgoing;
		nextEdges = next.outgoing;
		rank = current.rank + 1;

		for (int i = 0; i < currentEdges.size(); i++) {
			Edge currentEdge = currentEdges.getEdge(i);
			iCurrent = currentEdge.getIndexForRank(rank);
			for (int j = 0; j < nextEdges.size(); j++) {
				iNext = nextEdges.getEdge(j).getIndexForRank(rank);
				if (iNext < iCurrent)
					crossCount++;
				else if (iNext > iCurrent)
					invertedCrossCount++;
				else {
					// edges go to the same location
					int offsetDiff = nextEdges.getEdge(j).getTargetOffset()
							- currentEdge.getTargetOffset();
					if (offsetDiff < 0)
						crossCount++;
					else if (offsetDiff > 0)
						invertedCrossCount++;
				}
			}
		}
		if (invertedCrossCount < crossCount)
			return true;
		return false;
	}

	private void swapNodes(Node current, Node next, Rank rank) {
		int index = rank.indexOf(current);
		rank.set(index + 1, current);
		rank.set(index, next);
		index = current.index;
		current.index = next.index;
		next.index = index;
	}

	/**
	 * @see GraphVisitor#visit(org.eclipse.draw2d.graph.DirectedGraph)
	 */
	public void visit(DirectedGraph g) {
		boolean flag;
		do {
			flag = false;
			for (int r = 0; r < g.ranks.size(); r++) {
				Rank rank = g.ranks.getRank(r);
				for (int n = 0; n < rank.count() - 1; n++) {
					Node currentNode = rank.getNode(n);
					Node nextNode = rank.getNode(n + 1);
					if (shouldSwap(currentNode, nextNode)) {
						swapNodes(currentNode, nextNode, rank);
						flag = true;
						n = Math.max(0, n - 2);
					}
				}
			}
		} while (flag);
	}

}