CollapsedEdges.java

/*******************************************************************************
 * Copyright (c) 2005 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;

/**
 * Contains the information from all edges going from a given cluster to some other
 * cluster.  An edge with minimal slack as chosen to maintain the link between clusters.
 * The weight and any slack more than the minimal edge's slack is tracked for all other
 * edges.
 * @since 3.1
 */
class CollapsedEdges {

	/**
	 * The total weight of the collapsed edges.
	 */
	int collapsedWeight;
	int collapsedCount;
	
	/**
	 * The total amount of weighted difference in the collapsed edges slack and the
	 * tightest edge's slack.
	 */
	int overage;
	int unOverage;
	Edge tightestEdge;
	
	CollapsedEdges(Edge edge) {
		tightestEdge = edge;
		collapsedWeight = edge.weight;
		collapsedCount++;
	}
	
	public int getWeightedPull() {
		return tightestEdge.getSlack() * collapsedWeight + overage;
	}

	public boolean isTight() {
		return tightestEdge.getSlack() == 0;
	}
	
	/**
	 * Compares the given edge to the current tightest edge.  If the given edge is tighter
	 * than the current, the current tightest is returned.  Otherwise, the edge itself is
	 * returned.  The returned edge would be the one to remove from the graph.
	 * @param candidate another edge
	 * @return the edge which is not the tightest edge
	 * @since 3.1
	 */
	Edge processEdge(Edge candidate) {
		collapsedCount++;
		if (candidate.getSlack() < tightestEdge.getSlack()) {
			overage += collapsedWeight * (tightestEdge.getSlack() - candidate.getSlack());
			Edge temp = tightestEdge;
			tightestEdge = candidate;
			collapsedWeight += candidate.weight;
			return temp;
		} else {
			int over = candidate.getSlack() - tightestEdge.getSlack();
			unOverage += over;
			overage += candidate.weight * over;
			collapsedWeight += candidate.weight;
			return candidate;
		}
	}
}