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A GWT-compatible port of JBox2D, for use with PlayN games.
There is a newer version: 1.9.1
/*******************************************************************************
 * Copyright (c) 2011, Daniel Murphy
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the  nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL DANIEL MURPHY BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 ******************************************************************************/
/**
 * Created at 12:11:41 PM Jan 23, 2011
 */
package org.jbox2d.dynamics.joints;

import org.jbox2d.common.Settings;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.Body;

/**
 * Pulley joint definition. This requires two ground anchors,
 * two dynamic body anchor points, max lengths for each side,
 * and a pulley ratio.
 * 
 * @author Daniel Murphy
 */
public class PulleyJointDef extends JointDef {
	
	/**
	 * The first ground anchor in world coordinates. This point never moves.
	 */
	public Vec2 groundAnchorA;
	
	/**
	 * The second ground anchor in world coordinates. This point never moves.
	 */
	public Vec2 groundAnchorB;
	
	/**
	 * The local anchor point relative to bodyA's origin.
	 */
	public Vec2 localAnchorA;
	
	/**
	 * The local anchor point relative to bodyB's origin.
	 */
	public Vec2 localAnchorB;
	
	/**
	 * The a reference length for the segment attached to bodyA.
	 */
	public float lengthA;
	
	/**
	 * The maximum length of the segment attached to bodyA.
	 */
	public float maxLengthA;
	
	/**
	 * The a reference length for the segment attached to bodyB.
	 */
	public float lengthB;
	
	/**
	 * The maximum length of the segment attached to bodyB.
	 */
	public float maxLengthB;
	
	/**
	 * The pulley ratio, used to simulate a block-and-tackle.
	 */
	public float ratio;
	
	public PulleyJointDef() {
		type = JointType.PULLEY;
		groundAnchorA = new Vec2(-1.0f, 1.0f);
		groundAnchorB = new Vec2(1.0f, 1.0f);
		localAnchorA = new Vec2(-1.0f, 0.0f);
		localAnchorB = new Vec2(1.0f, 0.0f);
		lengthA = 0.0f;
		maxLengthA = 0.0f;
		lengthB = 0.0f;
		maxLengthB = 0.0f;
		ratio = 1.0f;
		collideConnected = true;
	}
	
	/**
	 * Initialize the bodies, anchors, lengths, max lengths, and ratio using the world
	 * anchors.
	 */
	public void initialize(Body b1, Body b2, Vec2 ga1, Vec2 ga2, Vec2 anchor1, Vec2 anchor2, float r) {
		bodyA = b1;
		bodyB = b2;
		groundAnchorA = ga1;
		groundAnchorB = ga2;
		localAnchorA = bodyA.getLocalPoint(anchor1);
		localAnchorB = bodyB.getLocalPoint(anchor2);
		Vec2 d1 = anchor1.sub(ga1);
		lengthA = d1.length();
		Vec2 d2 = anchor2.sub(ga2);
		lengthB = d2.length();
		ratio = r;
		assert (ratio > Settings.EPSILON);
		float C = lengthA + ratio * lengthB;
		maxLengthA = C - ratio * PulleyJoint.MIN_PULLEY_LENGTH;
		maxLengthB = (C - PulleyJoint.MIN_PULLEY_LENGTH) / ratio;
	}
}