DirectedGraphLayout.java

/*******************************************************************************
 * Copyright (c) 2003, 2007 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;

import java.util.ArrayList;
import java.util.List;

/**
 * Performs a graph layout of a <code>DirectedGraph</code>.  The directed graph must meet
 * the following conditions:
 * <UL>
 *   <LI>The graph must be connected.
 *   <LI>All edge's must be added to the graph's {@link DirectedGraph#edges edges} list
 *   exactly once.
 *   <LI>All nodes must be added to the graph's {@link DirectedGraph#nodes nodes} list
 *   exactly once.
 * </UL>
 * 
 * This algorithm will:
 * <UL>
 *   <LI>break cycles by inverting a set of feedback edges. Feedback edges will have the
 *   flag {@link Edge#isFeedback} set to <code>true</code>.  The following statements are
 *   true with respect to the inverted edge. When the algorithm completes, it will invert
 *   the edges again, but will leave the feedback flags set.
 *   <LI>for each node <em>n</em>, assign n to a "rank" R(n), such that: for each edge (m,
 *   n) in n.incoming, R(m)<=R(n)-(m,n).delta.   The total weighted edge lengths shall be
 *   no greater than is necessary to meet this requirement for all edges in the graph.
 *   <LI>attempt to order the nodes in their ranks as to minimize crossings.
 *   <LI>assign <em>y</em> coordinates to each node based on its rank.  The spacing
 *   between ranks is the sum of the bottom padding of the previous rank, and the top
 *   padding of the next rank.
 *   <LI>assign <em>x</em> coordinates such that the graph is easily readable.  The exact
 *   behavior is undefined, but will favor edge's with higher {@link Edge#weight}s.  The
 *   minimum x value assigned to a node or bendpoint will be 0.
 *   <LI>assign <em>bendpoints</em> to all edge's which span more than 1 rank.
 * </UL>
 * <P>For each NODE:
 * <UL>
 *   <LI>The x coordinate will be assigned a value >= 0
 *   <LI>The y coordinate will be assigned a value >= 0
 *   <LI>The rank will be assigned a value >=0
 *   <LI>The height will be set to the height of the tallest node on the same row
 * </UL>
 * <P>For each EDGE:
 * <UL>
 *   <LI>If an edge spans more than 1 row, it will have a list of   {@link
 * org.eclipse.draw2d.graph.Edge#vNodes virtual} nodes.  The virtual nodes will   be
 * assigned an x coordinate indicating the routing path for that edge.
 *   <LI>If an edge is a feedback edge, it's <code>isFeedback</code> flag will be set,  
 * and if it has virtual nodes, they will be in reverse order (bottom-up).
 * </UL>
 * <P>This class is not guaranteed to produce the same results for each invocation.
 * @author Randy Hudson
 * @since 2.1.2
 */
public class DirectedGraphLayout {

List steps = new ArrayList();

/**
 * @since 3.1
 */
public DirectedGraphLayout() {
	init();
}

void init() {
	steps.add(new TransposeMetrics());
	steps.add(new BreakCycles());
	steps.add(new RouteEdges());
	steps.add(new InitialRankSolver());
	steps.add(new TightSpanningTreeSolver());
	steps.add(new RankAssignmentSolver());
	steps.add(new PopulateRanks());
	steps.add(new VerticalPlacement());
	steps.add(new MinCross());
	steps.add(new LocalOptimizer());
	steps.add(new HorizontalPlacement());
}

/**
 * Lays out the given graph
 * @param graph the graph to layout
 */
public void visit(DirectedGraph graph) {
	if (graph.nodes.isEmpty())
		return;
	for (int i = 0; i < steps.size(); i++) {
		GraphVisitor visitor = (GraphVisitor)steps.get(i);
		visitor.visit(graph);
	}
	for (int i = steps.size() - 1; i >= 0; i--) {
		GraphVisitor visitor = (GraphVisitor)steps.get(i);
		visitor.revisit(graph);
	}
}

}