/*******************************************************************************
* Copyright (c) 2013, 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.
*
* 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 THE COPYRIGHT HOLDER OR CONTRIBUTORS 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.
******************************************************************************/
package org.jbox2d.dynamics.joints;
import org.jbox2d.common.Mat22;
import org.jbox2d.common.MathUtils;
import org.jbox2d.common.Rot;
import org.jbox2d.common.Settings;
import org.jbox2d.common.Transform;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.SolverData;
import org.jbox2d.pooling.IWorldPool;
/**
* A mouse joint is used to make a point on a body track a specified world point. This a soft
* constraint with a maximum force. This allows the constraint to stretch and without applying huge
* forces. NOTE: this joint is not documented in the manual because it was developed to be used in
* the testbed. If you want to learn how to use the mouse joint, look at the testbed.
*
* @author Daniel
*/
public class MouseJoint extends Joint {
private final Vec2 m_localAnchorB = new Vec2();
private final Vec2 m_targetA = new Vec2();
private float m_frequencyHz;
private float m_dampingRatio;
private float m_beta;
// Solver shared
private final Vec2 m_impulse = new Vec2();
private float m_maxForce;
private float m_gamma;
// Solver temp
private int m_indexB;
private final Vec2 m_rB = new Vec2();
private final Vec2 m_localCenterB = new Vec2();
private float m_invMassB;
private float m_invIB;
private final Mat22 m_mass = new Mat22();
private final Vec2 m_C = new Vec2();
protected MouseJoint(IWorldPool argWorld, MouseJointDef def) {
super(argWorld, def);
assert (def.target.isValid());
assert (def.maxForce >= 0);
assert (def.frequencyHz >= 0);
assert (def.dampingRatio >= 0);
m_targetA.set(def.target);
Transform.mulTransToOutUnsafe(m_bodyB.getTransform(), m_targetA, m_localAnchorB);
m_maxForce = def.maxForce;
m_impulse.setZero();
m_frequencyHz = def.frequencyHz;
m_dampingRatio = def.dampingRatio;
m_beta = 0;
m_gamma = 0;
}
@Override
public void getAnchorA(Vec2 argOut) {
argOut.set(m_targetA);
}
@Override
public void getAnchorB(Vec2 argOut) {
m_bodyB.getWorldPointToOut(m_localAnchorB, argOut);
}
@Override
public void getReactionForce(float invDt, Vec2 argOut) {
argOut.set(m_impulse).mulLocal(invDt);
}
@Override
public float getReactionTorque(float invDt) {
return invDt * 0.0f;
}
public void setTarget(Vec2 target) {
if (m_bodyB.isAwake() == false) {
m_bodyB.setAwake(true);
}
m_targetA.set(target);
}
public Vec2 getTarget() {
return m_targetA;
}
// / set/get the maximum force in Newtons.
public void setMaxForce(float force) {
m_maxForce = force;
}
public float getMaxForce() {
return m_maxForce;
}
// / set/get the frequency in Hertz.
public void setFrequency(float hz) {
m_frequencyHz = hz;
}
public float getFrequency() {
return m_frequencyHz;
}
// / set/get the damping ratio (dimensionless).
public void setDampingRatio(float ratio) {
m_dampingRatio = ratio;
}
public float getDampingRatio() {
return m_dampingRatio;
}
@Override
public void initVelocityConstraints(final SolverData data) {
m_indexB = m_bodyB.m_islandIndex;
m_localCenterB.set(m_bodyB.m_sweep.localCenter);
m_invMassB = m_bodyB.m_invMass;
m_invIB = m_bodyB.m_invI;
Vec2 cB = data.positions[m_indexB].c;
float aB = data.positions[m_indexB].a;
Vec2 vB = data.velocities[m_indexB].v;
float wB = data.velocities[m_indexB].w;
final Rot qB = pool.popRot();
qB.set(aB);
float mass = m_bodyB.getMass();
// Frequency
float omega = 2.0f * MathUtils.PI * m_frequencyHz;
// Damping coefficient
float d = 2.0f * mass * m_dampingRatio * omega;
// Spring stiffness
float k = mass * (omega * omega);
// magic formulas
// gamma has units of inverse mass.
// beta has units of inverse time.
float h = data.step.dt;
assert (d + h * k > Settings.EPSILON);
m_gamma = h * (d + h * k);
if (m_gamma != 0.0f) {
m_gamma = 1.0f / m_gamma;
}
m_beta = h * k * m_gamma;
Vec2 temp = pool.popVec2();
// Compute the effective mass matrix.
Rot.mulToOutUnsafe(qB, temp.set(m_localAnchorB).subLocal(m_localCenterB), m_rB);
// K = [(1/m1 + 1/m2) * eye(2) - skew(r1) * invI1 * skew(r1) - skew(r2) * invI2 * skew(r2)]
// = [1/m1+1/m2 0 ] + invI1 * [r1.y*r1.y -r1.x*r1.y] + invI2 * [r1.y*r1.y -r1.x*r1.y]
// [ 0 1/m1+1/m2] [-r1.x*r1.y r1.x*r1.x] [-r1.x*r1.y r1.x*r1.x]
final Mat22 K = pool.popMat22();
K.ex.x = m_invMassB + m_invIB * m_rB.y * m_rB.y + m_gamma;
K.ex.y = -m_invIB * m_rB.x * m_rB.y;
K.ey.x = K.ex.y;
K.ey.y = m_invMassB + m_invIB * m_rB.x * m_rB.x + m_gamma;
K.invertToOut(m_mass);
m_C.set(cB).addLocal(m_rB).subLocal(m_targetA);
m_C.mulLocal(m_beta);
// Cheat with some damping
wB *= 0.98f;
if (data.step.warmStarting) {
m_impulse.mulLocal(data.step.dtRatio);
vB.x += m_invMassB * m_impulse.x;
vB.y += m_invMassB * m_impulse.y;
wB += m_invIB * Vec2.cross(m_rB, m_impulse);
} else {
m_impulse.setZero();
}
// data.velocities[m_indexB].v.set(vB);
data.velocities[m_indexB].w = wB;
pool.pushVec2(1);
pool.pushMat22(1);
pool.pushRot(1);
}
@Override
public boolean solvePositionConstraints(final SolverData data) {
return true;
}
@Override
public void solveVelocityConstraints(final SolverData data) {
Vec2 vB = data.velocities[m_indexB].v;
float wB = data.velocities[m_indexB].w;
// Cdot = v + cross(w, r)
final Vec2 Cdot = pool.popVec2();
Vec2.crossToOutUnsafe(wB, m_rB, Cdot);
Cdot.addLocal(vB);
final Vec2 impulse = pool.popVec2();
final Vec2 temp = pool.popVec2();
temp.set(m_impulse).mulLocal(m_gamma).addLocal(m_C).addLocal(Cdot).negateLocal();
Mat22.mulToOutUnsafe(m_mass, temp, impulse);
Vec2 oldImpulse = temp;
oldImpulse.set(m_impulse);
m_impulse.addLocal(impulse);
float maxImpulse = data.step.dt * m_maxForce;
if (m_impulse.lengthSquared() > maxImpulse * maxImpulse) {
m_impulse.mulLocal(maxImpulse / m_impulse.length());
}
impulse.set(m_impulse).subLocal(oldImpulse);
vB.x += m_invMassB * impulse.x;
vB.y += m_invMassB * impulse.y;
wB += m_invIB * Vec2.cross(m_rB, impulse);
// data.velocities[m_indexB].v.set(vB);
data.velocities[m_indexB].w = wB;
pool.pushVec2(3);
}
}