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

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 * Copyright (c) 2013, Daniel Murphy
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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;

/**
 * Revolute joint definition. This requires defining an anchor point where the bodies are joined.
 * The definition uses local anchor points so that the initial configuration can violate the
 * constraint slightly. You also need to specify the initial relative angle for joint limits. This
 * helps when saving and loading a game. The local anchor points are measured from the body's origin
 * rather than the center of mass because:

 * 
 * you might not know where the center of mass will be.
 * if you add/remove shapes from a body and recompute the mass, the joints will be broken.
 * 
 */
public class RevoluteJointDef extends JointDef {

  /**
   * The local anchor point relative to body1's origin.
   */
  public Vec2 localAnchorA;

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

  /**
   * The body2 angle minus body1 angle in the reference state (radians).
   */
  public float referenceAngle;

  /**
   * A flag to enable joint limits.
   */
  public boolean enableLimit;

  /**
   * The lower angle for the joint limit (radians).
   */
  public float lowerAngle;

  /**
   * The upper angle for the joint limit (radians).
   */
  public float upperAngle;

  /**
   * A flag to enable the joint motor.
   */
  public boolean enableMotor;

  /**
   * The desired motor speed. Usually in radians per second.
   */
  public float motorSpeed;

  /**
   * The maximum motor torque used to achieve the desired motor speed. Usually in N-m.
   */
  public float maxMotorTorque;

  public RevoluteJointDef() {
    super(JointType.REVOLUTE);
    localAnchorA = new Vec2(0.0f, 0.0f);
    localAnchorB = new Vec2(0.0f, 0.0f);
    referenceAngle = 0.0f;
    lowerAngle = 0.0f;
    upperAngle = 0.0f;
    maxMotorTorque = 0.0f;
    motorSpeed = 0.0f;
    enableLimit = false;
    enableMotor = false;
  }

  /**
   * Initialize the bodies, anchors, and reference angle using the world anchor.
   * 
   * @param b1
   * @param b2
   * @param anchor
   */
  public void initialize(final Body b1, final Body b2, final Vec2 anchor) {
    bodyA = b1;
    bodyB = b2;
    bodyA.getLocalPointToOut(anchor, localAnchorA);
    bodyB.getLocalPointToOut(anchor, localAnchorB);
    referenceAngle = bodyB.getAngle() - bodyA.getAngle();
  }
}