/*******************************************************************************
* Copyright (c) 2013, Daniel Murphy
* All rights reserved.
*
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* are permitted provided that the following conditions are met:
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*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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******************************************************************************/
/**
* 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.Rot;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.SolverData;
import org.jbox2d.pooling.IWorldPool;
/**
* @author Daniel Murphy
*/
public class FrictionJoint extends Joint {
private final Vec2 m_localAnchorA;
private final Vec2 m_localAnchorB;
// Solver shared
private final Vec2 m_linearImpulse;
private float m_angularImpulse;
private float m_maxForce;
private float m_maxTorque;
// Solver temp
private int m_indexA;
private int m_indexB;
private final Vec2 m_rA = new Vec2();
private final Vec2 m_rB = new Vec2();
private final Vec2 m_localCenterA = new Vec2();
private final Vec2 m_localCenterB = new Vec2();
private float m_invMassA;
private float m_invMassB;
private float m_invIA;
private float m_invIB;
private final Mat22 m_linearMass = new Mat22();
private float m_angularMass;
protected FrictionJoint(IWorldPool 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;
}
public Vec2 getLocalAnchorA() {
return m_localAnchorA;
}
public Vec2 getLocalAnchorB() {
return m_localAnchorB;
}
@Override
public void getAnchorA(Vec2 argOut) {
m_bodyA.getWorldPointToOut(m_localAnchorA, argOut);
}
@Override
public void getAnchorB(Vec2 argOut) {
m_bodyB.getWorldPointToOut(m_localAnchorB, argOut);
}
@Override
public void getReactionForce(float inv_dt, Vec2 argOut) {
argOut.set(m_linearImpulse).mulLocal(inv_dt);
}
@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(final SolverData data) {
m_indexA = m_bodyA.m_islandIndex;
m_indexB = m_bodyB.m_islandIndex;
m_localCenterA.set(m_bodyA.m_sweep.localCenter);
m_localCenterB.set(m_bodyB.m_sweep.localCenter);
m_invMassA = m_bodyA.m_invMass;
m_invMassB = m_bodyB.m_invMass;
m_invIA = m_bodyA.m_invI;
m_invIB = m_bodyB.m_invI;
float aA = data.positions[m_indexA].a;
Vec2 vA = data.velocities[m_indexA].v;
float wA = data.velocities[m_indexA].w;
float aB = data.positions[m_indexB].a;
Vec2 vB = data.velocities[m_indexB].v;
float wB = data.velocities[m_indexB].w;
final Vec2 temp = pool.popVec2();
final Rot qA = pool.popRot();
final Rot qB = pool.popRot();
qA.set(aA);
qB.set(aB);
// Compute the effective mass matrix.
Rot.mulToOutUnsafe(qA, temp.set(m_localAnchorA).subLocal(m_localCenterA), m_rA);
Rot.mulToOutUnsafe(qB, temp.set(m_localAnchorB).subLocal(m_localCenterB), m_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 = m_invMassA, mB = m_invMassB;
float iA = m_invIA, iB = m_invIB;
final Mat22 K = pool.popMat22();
K.ex.x = mA + mB + iA * m_rA.y * m_rA.y + iB * m_rB.y * m_rB.y;
K.ex.y = -iA * m_rA.x * m_rA.y - iB * m_rB.x * m_rB.y;
K.ey.x = K.ex.y;
K.ey.y = mA + mB + iA * m_rA.x * m_rA.x + iB * m_rB.x * m_rB.x;
K.invertToOut(m_linearMass);
m_angularMass = iA + iB;
if (m_angularMass > 0.0f) {
m_angularMass = 1.0f / m_angularMass;
}
if (data.step.warmStarting) {
// Scale impulses to support a variable time step.
m_linearImpulse.mulLocal(data.step.dtRatio);
m_angularImpulse *= data.step.dtRatio;
final Vec2 P = pool.popVec2();
P.set(m_linearImpulse);
temp.set(P).mulLocal(mA);
vA.subLocal(temp);
wA -= iA * (Vec2.cross(m_rA, P) + m_angularImpulse);
temp.set(P).mulLocal(mB);
vB.addLocal(temp);
wB += iB * (Vec2.cross(m_rB, P) + m_angularImpulse);
pool.pushVec2(1);
} else {
m_linearImpulse.setZero();
m_angularImpulse = 0.0f;
}
// data.velocities[m_indexA].v.set(vA);
if( data.velocities[m_indexA].w != wA) {
assert(data.velocities[m_indexA].w != wA);
}
data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v.set(vB);
data.velocities[m_indexB].w = wB;
pool.pushRot(2);
pool.pushVec2(1);
pool.pushMat22(1);
}
@Override
public void solveVelocityConstraints(final SolverData data) {
Vec2 vA = data.velocities[m_indexA].v;
float wA = data.velocities[m_indexA].w;
Vec2 vB = data.velocities[m_indexB].v;
float wB = data.velocities[m_indexB].w;
float mA = m_invMassA, mB = m_invMassB;
float iA = m_invIA, iB = m_invIB;
float h = data.step.dt;
// Solve angular friction
{
float Cdot = wB - wA;
float impulse = -m_angularMass * Cdot;
float oldImpulse = m_angularImpulse;
float maxImpulse = h * 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.crossToOutUnsafe(wA, m_rA, temp);
Vec2.crossToOutUnsafe(wB, m_rB, Cdot);
Cdot.addLocal(vB).subLocal(vA).subLocal(temp);
final Vec2 impulse = pool.popVec2();
Mat22.mulToOutUnsafe(m_linearMass, Cdot, impulse);
impulse.negateLocal();
final Vec2 oldImpulse = pool.popVec2();
oldImpulse.set(m_linearImpulse);
m_linearImpulse.addLocal(impulse);
float maxImpulse = h * 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(m_rA, impulse);
temp.set(impulse).mulLocal(mB);
vB.addLocal(temp);
wB += iB * Vec2.cross(m_rB, impulse);
}
// data.velocities[m_indexA].v.set(vA);
if( data.velocities[m_indexA].w != wA) {
assert(data.velocities[m_indexA].w != wA);
}
data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v.set(vB);
data.velocities[m_indexB].w = wB;
pool.pushVec2(4);
}
@Override
public boolean solvePositionConstraints(final SolverData data) {
return true;
}
}