org.jbox2d.dynamics.joints.DistanceJointDef Maven / Gradle / Ivy

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/*
 * JBox2D - A Java Port of Erin Catto's Box2D
 * 
 * JBox2D homepage: http://jbox2d.sourceforge.net/
 * Box2D homepage: http://www.box2d.org
 * 
 * This software is provided 'as-is', without any express or implied
 * warranty.  In no event will the authors be held liable for any damages
 * arising from the use of this software.
 * 
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 * 
 * 1. The origin of this software must not be misrepresented; you must not
 * claim that you wrote the original software. If you use this software
 * in a product, an acknowledgment in the product documentation would be
 * appreciated but is not required.
 * 2. Altered source versions must be plainly marked as such, and must not be
 * misrepresented as being the original software.
 * 3. This notice may not be removed or altered from any source distribution.
 */

package org.jbox2d.dynamics.joints;

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

//Updated to rev 56->130->142 of b2DistanceJoint.cpp/.h

/**
 * Distance joint definition. This requires defining an anchor point on both bodies and the non-zero
 * length of the distance joint. The definition uses local anchor points so that the initial
 * configuration can violate the constraint slightly. This helps when saving and loading a game.
 * 
 * @warning Do not use a zero or short length.
 */
public class DistanceJointDef extends JointDef {
  /** The local anchor point relative to body1's origin. */
  public final Vec2 localAnchorA;

  /** The local anchor point relative to body2's origin. */
  public final Vec2 localAnchorB;

  /** The equilibrium length between the anchor points. */
  public float length;

  /**
   * The mass-spring-damper frequency in Hertz.
   */
  public float frequencyHz;

  /**
   * The damping ratio. 0 = no damping, 1 = critical damping.
   */
  public float dampingRatio;

  public DistanceJointDef() {
    super(JointType.DISTANCE);
    localAnchorA = new Vec2(0.0f, 0.0f);
    localAnchorB = new Vec2(0.0f, 0.0f);
    length = 1.0f;
    frequencyHz = 0.0f;
    dampingRatio = 0.0f;
  }

  /**
   * Initialize the bodies, anchors, and length using the world anchors.
   * 
   * @param b1 First body
   * @param b2 Second body
   * @param anchor1 World anchor on first body
   * @param anchor2 World anchor on second body
   */
  public void initialize(final Body b1, final Body b2, final Vec2 anchor1, final Vec2 anchor2) {
    bodyA = b1;
    bodyB = b2;
    localAnchorA.set(bodyA.getLocalPoint(anchor1));
    localAnchorB.set(bodyB.getLocalPoint(anchor2));
    Vec2 d = anchor2.sub(anchor1);
    length = d.length();
  }
}