/*******************************************************************************
* 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 <organization> 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 7:27:32 AM Jan 20, 2011
*/
package org.jbox2d.dynamics.joints;
import org.jbox2d.common.Mat22;
import org.jbox2d.common.MathUtils;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.Body;
import org.jbox2d.dynamics.TimeStep;
import org.jbox2d.pooling.WorldPool;
/**
* @author Daniel Murphy
*/
public class FrictionJoint extends Joint {
private final Vec2 m_localAnchorA;
private final Vec2 m_localAnchorB;
private final Mat22 m_linearMass;
private float m_angularMass;
private final Vec2 m_linearImpulse;
private float m_angularImpulse;
private float m_maxForce;
private float m_maxTorque;
/**
* @param argWorldPool
* @param def
*/
public FrictionJoint(WorldPool argWorldPool, FrictionJointDef def) {
super(argWorldPool, def);
m_localAnchorA = new Vec2(def.localAnchorA);
m_localAnchorB = new Vec2(def.localAnchorB);
m_linearImpulse = new Vec2();
m_angularImpulse = 0.0f;
m_maxForce = def.maxForce;
m_maxTorque = def.maxTorque;
m_linearMass = new Mat22();
}
/**
* @see org.jbox2d.dynamics.joints.Joint#getAnchorA(org.jbox2d.common.Vec2)
*/
@Override
public void getAnchorA(Vec2 argOut) {
m_bodyA.getWorldPointToOut(m_localAnchorA, argOut);
}
/**
* @see org.jbox2d.dynamics.joints.Joint#getAnchorB(org.jbox2d.common.Vec2)
*/
@Override
public void getAnchorB(Vec2 argOut) {
m_bodyB.getWorldPointToOut(m_localAnchorB, argOut);
}
/**
* @see org.jbox2d.dynamics.joints.Joint#getReactionForce(float,
* org.jbox2d.common.Vec2)
*/
@Override
public void getReactionForce(float inv_dt, Vec2 argOut) {
argOut.set(m_linearImpulse).mulLocal(inv_dt);
}
/**
* @see org.jbox2d.dynamics.joints.Joint#getReactionTorque(float)
*/
@Override
public float getReactionTorque(float inv_dt) {
return inv_dt * m_angularImpulse;
}
public void setMaxForce(float force) {
assert (force >= 0.0f);
m_maxForce = force;
}
public float getMaxForce() {
return m_maxForce;
}
public void setMaxTorque(float torque) {
assert (torque >= 0.0f);
m_maxTorque = torque;
}
public float getMaxTorque() {
return m_maxTorque;
}
/**
* @see org.jbox2d.dynamics.joints.Joint#initVelocityConstraints(org.jbox2d.dynamics.TimeStep)
*/
@Override
public void initVelocityConstraints(TimeStep step) {
Body bA = m_bodyA;
Body bB = m_bodyB;
// Compute the effective mass matrix.
final Vec2 rA = pool.popVec2();
final Vec2 rB = pool.popVec2();
rA.set(m_localAnchorA).subLocal(bA.getLocalCenter());
rB.set(m_localAnchorB).subLocal(bB.getLocalCenter());
Mat22.mulToOut(bA.getTransform().R, rA, rA);
Mat22.mulToOut(bB.getTransform().R, rB, rB);
// J = [-I -r1_skew I r2_skew]
// [ 0 -1 0 1]
// r_skew = [-ry; rx]
// Matlab
// K = [ mA+r1y^2*iA+mB+r2y^2*iB, -r1y*iA*r1x-r2y*iB*r2x, -r1y*iA-r2y*iB]
// [ -r1y*iA*r1x-r2y*iB*r2x, mA+r1x^2*iA+mB+r2x^2*iB, r1x*iA+r2x*iB]
// [ -r1y*iA-r2y*iB, r1x*iA+r2x*iB, iA+iB]
float mA = bA.m_invMass, mB = bB.m_invMass;
float iA = bA.m_invI, iB = bB.m_invI;
final Mat22 K1 = pool.popMat22();
K1.m11 = mA + mB;
K1.m21 = 0.0f;
K1.m12 = 0.0f;
K1.m22 = mA + mB;
final Mat22 K2 = pool.popMat22();
K2.m11 = iA * rA.y * rA.y;
K2.m21 = -iA * rA.x * rA.y;
K2.m12 = -iA * rA.x * rA.y;
K2.m22 = iA * rA.x * rA.x;
final Mat22 K3 = pool.popMat22();
K3.m11 = iB * rB.y * rB.y;
K3.m21 = -iB * rB.x * rB.y;
K3.m12 = -iB * rB.x * rB.y;
K3.m22 = iB * rB.x * rB.x;
K1.addLocal(K2).addLocal(K3);
m_linearMass.set(K1).invertLocal();
m_angularMass = iA + iB;
if (m_angularMass > 0.0f) {
m_angularMass = 1.0f / m_angularMass;
}
if (step.warmStarting) {
// Scale impulses to support a variable time step.
m_linearImpulse.mulLocal(step.dtRatio);
m_angularImpulse *= step.dtRatio;
final Vec2 P = pool.popVec2();
P.set(m_linearImpulse.x, m_linearImpulse.y);
final Vec2 temp = pool.popVec2();
temp.set(P).mulLocal(mA);
bA.m_linearVelocity.subLocal(temp);
bA.m_angularVelocity -= iA * (Vec2.cross(rA, P) + m_angularImpulse);
temp.set(P).mulLocal(mB);
bB.m_linearVelocity.addLocal(temp);
bB.m_angularVelocity += iB * (Vec2.cross(rB, P) + m_angularImpulse);
pool.pushVec2(2);
}
else {
m_linearImpulse.setZero();
m_angularImpulse = 0.0f;
}
pool.pushVec2(2);
pool.pushMat22(3);
}
/**
* @see org.jbox2d.dynamics.joints.Joint#solveVelocityConstraints(org.jbox2d.dynamics.TimeStep)
*/
@Override
public void solveVelocityConstraints(TimeStep step) {
Body bA = m_bodyA;
Body bB = m_bodyB;
final Vec2 vA = bA.m_linearVelocity;
float wA = bA.m_angularVelocity;
final Vec2 vB = bB.m_linearVelocity;
float wB = bB.m_angularVelocity;
float mA = bA.m_invMass, mB = bB.m_invMass;
float iA = bA.m_invI, iB = bB.m_invI;
final Vec2 rA = pool.popVec2();
final Vec2 rB = pool.popVec2();
rA.set(m_localAnchorA).subLocal(bA.getLocalCenter());
rB.set(m_localAnchorB).subLocal(bB.getLocalCenter());
Mat22.mulToOut(bA.getTransform().R, rA, rA);
Mat22.mulToOut(bB.getTransform().R, rB, rB);
// Solve angular friction
{
float Cdot = wB - wA;
float impulse = -m_angularMass * Cdot;
float oldImpulse = m_angularImpulse;
float maxImpulse = step.dt * m_maxTorque;
m_angularImpulse = MathUtils.clamp(m_angularImpulse + impulse, -maxImpulse, maxImpulse);
impulse = m_angularImpulse - oldImpulse;
wA -= iA * impulse;
wB += iB * impulse;
}
// Solve linear friction
{
final Vec2 Cdot = pool.popVec2();
final Vec2 temp = pool.popVec2();
Vec2.crossToOut(wA, rA, temp);
Vec2.crossToOut(wB, rB, Cdot);
Cdot.addLocal(vB).subLocal(vA).subLocal(temp);
final Vec2 impulse = pool.popVec2();
Mat22.mulToOut(m_linearMass, Cdot, impulse);
impulse.negateLocal();
final Vec2 oldImpulse = pool.popVec2();
oldImpulse.set(m_linearImpulse);
m_linearImpulse.addLocal(impulse);
float maxImpulse = step.dt * m_maxForce;
if (m_linearImpulse.lengthSquared() > maxImpulse * maxImpulse) {
m_linearImpulse.normalize();
m_linearImpulse.mulLocal(maxImpulse);
}
impulse.set(m_linearImpulse).subLocal(oldImpulse);
temp.set(impulse).mulLocal(mA);
vA.subLocal(temp);
wA -= iA * Vec2.cross(rA, impulse);
temp.set(impulse).mulLocal(mB);
vB.addLocal(temp);
wB += iB * Vec2.cross(rB, impulse);
}
pool.pushVec2(6);
bA.m_angularVelocity = wA;
bB.m_angularVelocity = wB;
}
/**
* @see org.jbox2d.dynamics.joints.Joint#solvePositionConstraints(float)
*/
@Override
public boolean solvePositionConstraints(float baumgarte) {
return true;
}
}