/*******************************************************************************
* 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.
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*
* 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
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* IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
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* POSSIBILITY OF SUCH DAMAGE.
******************************************************************************/
package org.jbox2d.dynamics.joints;
import org.jbox2d.common.Mat22;
import org.jbox2d.common.Mat33;
import org.jbox2d.common.MathUtils;
import org.jbox2d.common.Rot;
import org.jbox2d.common.Settings;
import org.jbox2d.common.Vec2;
import org.jbox2d.common.Vec3;
import org.jbox2d.dynamics.Body;
import org.jbox2d.dynamics.SolverData;
import org.jbox2d.pooling.IWorldPool;
//Point-to-point constraint
//C = p2 - p1
//Cdot = v2 - v1
// = v2 + cross(w2, r2) - v1 - cross(w1, r1)
//J = [-I -r1_skew I r2_skew ]
//Identity used:
//w k % (rx i + ry j) = w * (-ry i + rx j)
//Motor constraint
//Cdot = w2 - w1
//J = [0 0 -1 0 0 1]
//K = invI1 + invI2
/**
* A revolute joint constrains two bodies to share a common point while they are free to rotate
* about the point. The relative rotation about the shared point is the joint angle. You can limit
* the relative rotation with a joint limit that specifies a lower and upper angle. You can use a
* motor to drive the relative rotation about the shared point. A maximum motor torque is provided
* so that infinite forces are not generated.
*
* @author Daniel Murphy
*/
public class RevoluteJoint extends Joint {
// Solver shared
protected final Vec2 m_localAnchorA = new Vec2();
protected final Vec2 m_localAnchorB = new Vec2();
private final Vec3 m_impulse = new Vec3();
private float m_motorImpulse;
private boolean m_enableMotor;
private float m_maxMotorTorque;
private float m_motorSpeed;
private boolean m_enableLimit;
protected float m_referenceAngle;
private float m_lowerAngle;
private float m_upperAngle;
// 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 Mat33 m_mass = new Mat33(); // effective mass for point-to-point constraint.
private float m_motorMass; // effective mass for motor/limit angular constraint.
private LimitState m_limitState;
protected RevoluteJoint(IWorldPool argWorld, RevoluteJointDef def) {
super(argWorld, def);
m_localAnchorA.set(def.localAnchorA);
m_localAnchorB.set(def.localAnchorB);
m_referenceAngle = def.referenceAngle;
m_motorImpulse = 0;
m_lowerAngle = def.lowerAngle;
m_upperAngle = def.upperAngle;
m_maxMotorTorque = def.maxMotorTorque;
m_motorSpeed = def.motorSpeed;
m_enableLimit = def.enableLimit;
m_enableMotor = def.enableMotor;
m_limitState = LimitState.INACTIVE;
}
@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;
// Vec2 cA = data.positions[m_indexA].c;
float aA = data.positions[m_indexA].a;
Vec2 vA = data.velocities[m_indexA].v;
float wA = data.velocities[m_indexA].w;
// 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 qA = pool.popRot();
final Rot qB = pool.popRot();
final Vec2 temp = pool.popVec2();
qA.set(aA);
qB.set(aB);
// Compute the effective masses.
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;
boolean fixedRotation = (iA + iB == 0.0f);
m_mass.ex.x = mA + mB + m_rA.y * m_rA.y * iA + m_rB.y * m_rB.y * iB;
m_mass.ey.x = -m_rA.y * m_rA.x * iA - m_rB.y * m_rB.x * iB;
m_mass.ez.x = -m_rA.y * iA - m_rB.y * iB;
m_mass.ex.y = m_mass.ey.x;
m_mass.ey.y = mA + mB + m_rA.x * m_rA.x * iA + m_rB.x * m_rB.x * iB;
m_mass.ez.y = m_rA.x * iA + m_rB.x * iB;
m_mass.ex.z = m_mass.ez.x;
m_mass.ey.z = m_mass.ez.y;
m_mass.ez.z = iA + iB;
m_motorMass = iA + iB;
if (m_motorMass > 0.0f) {
m_motorMass = 1.0f / m_motorMass;
}
if (m_enableMotor == false || fixedRotation) {
m_motorImpulse = 0.0f;
}
if (m_enableLimit && fixedRotation == false) {
float jointAngle = aB - aA - m_referenceAngle;
if (MathUtils.abs(m_upperAngle - m_lowerAngle) < 2.0f * Settings.angularSlop) {
m_limitState = LimitState.EQUAL;
} else if (jointAngle <= m_lowerAngle) {
if (m_limitState != LimitState.AT_LOWER) {
m_impulse.z = 0.0f;
}
m_limitState = LimitState.AT_LOWER;
} else if (jointAngle >= m_upperAngle) {
if (m_limitState != LimitState.AT_UPPER) {
m_impulse.z = 0.0f;
}
m_limitState = LimitState.AT_UPPER;
} else {
m_limitState = LimitState.INACTIVE;
m_impulse.z = 0.0f;
}
} else {
m_limitState = LimitState.INACTIVE;
}
if (data.step.warmStarting) {
final Vec2 P = pool.popVec2();
// Scale impulses to support a variable time step.
m_impulse.x *= data.step.dtRatio;
m_impulse.y *= data.step.dtRatio;
m_motorImpulse *= data.step.dtRatio;
P.x = m_impulse.x;
P.y = m_impulse.y;
vA.x -= mA * P.x;
vA.y -= mA * P.y;
wA -= iA * (Vec2.cross(m_rA, P) + m_motorImpulse + m_impulse.z);
vB.x += mB * P.x;
vB.y += mB * P.y;
wB += iB * (Vec2.cross(m_rB, P) + m_motorImpulse + m_impulse.z);
pool.pushVec2(1);
} else {
m_impulse.setZero();
m_motorImpulse = 0.0f;
}
// data.velocities[m_indexA].v.set(vA);
data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v.set(vB);
data.velocities[m_indexB].w = wB;
pool.pushVec2(1);
pool.pushRot(2);
}
@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;
boolean fixedRotation = (iA + iB == 0.0f);
// Solve motor constraint.
if (m_enableMotor && m_limitState != LimitState.EQUAL && fixedRotation == false) {
float Cdot = wB - wA - m_motorSpeed;
float impulse = -m_motorMass * Cdot;
float oldImpulse = m_motorImpulse;
float maxImpulse = data.step.dt * m_maxMotorTorque;
m_motorImpulse = MathUtils.clamp(m_motorImpulse + impulse, -maxImpulse, maxImpulse);
impulse = m_motorImpulse - oldImpulse;
wA -= iA * impulse;
wB += iB * impulse;
}
final Vec2 temp = pool.popVec2();
// Solve limit constraint.
if (m_enableLimit && m_limitState != LimitState.INACTIVE && fixedRotation == false) {
final Vec2 Cdot1 = pool.popVec2();
final Vec3 Cdot = pool.popVec3();
// Solve point-to-point constraint
Vec2.crossToOutUnsafe(wA, m_rA, temp);
Vec2.crossToOutUnsafe(wB, m_rB, Cdot1);
Cdot1.addLocal(vB).subLocal(vA).subLocal(temp);
float Cdot2 = wB - wA;
Cdot.set(Cdot1.x, Cdot1.y, Cdot2);
Vec3 impulse = pool.popVec3();
m_mass.solve33ToOut(Cdot, impulse);
impulse.negateLocal();
if (m_limitState == LimitState.EQUAL) {
m_impulse.addLocal(impulse);
} else if (m_limitState == LimitState.AT_LOWER) {
float newImpulse = m_impulse.z + impulse.z;
if (newImpulse < 0.0f) {
final Vec2 rhs = pool.popVec2();
rhs.set(m_mass.ez.x, m_mass.ez.y).mulLocal(m_impulse.z).subLocal(Cdot1);
m_mass.solve22ToOut(rhs, temp);
impulse.x = temp.x;
impulse.y = temp.y;
impulse.z = -m_impulse.z;
m_impulse.x += temp.x;
m_impulse.y += temp.y;
m_impulse.z = 0.0f;
pool.pushVec2(1);
} else {
m_impulse.addLocal(impulse);
}
} else if (m_limitState == LimitState.AT_UPPER) {
float newImpulse = m_impulse.z + impulse.z;
if (newImpulse > 0.0f) {
final Vec2 rhs = pool.popVec2();
rhs.set(m_mass.ez.x, m_mass.ez.y).mulLocal(m_impulse.z).subLocal(Cdot1);
m_mass.solve22ToOut(rhs, temp);
impulse.x = temp.x;
impulse.y = temp.y;
impulse.z = -m_impulse.z;
m_impulse.x += temp.x;
m_impulse.y += temp.y;
m_impulse.z = 0.0f;
pool.pushVec2(1);
} else {
m_impulse.addLocal(impulse);
}
}
final Vec2 P = pool.popVec2();
P.set(impulse.x, impulse.y);
vA.x -= mA * P.x;
vA.y -= mA * P.y;
wA -= iA * (Vec2.cross(m_rA, P) + impulse.z);
vB.x += mB * P.x;
vB.y += mB * P.y;
wB += iB * (Vec2.cross(m_rB, P) + impulse.z);
pool.pushVec2(2);
pool.pushVec3(2);
} else {
// Solve point-to-point constraint
Vec2 Cdot = pool.popVec2();
Vec2 impulse = pool.popVec2();
Vec2.crossToOutUnsafe(wA, m_rA, temp);
Vec2.crossToOutUnsafe(wB, m_rB, Cdot);
Cdot.addLocal(vB).subLocal(vA).subLocal(temp);
m_mass.solve22ToOut(Cdot.negateLocal(), impulse); // just leave negated
m_impulse.x += impulse.x;
m_impulse.y += impulse.y;
vA.x -= mA * impulse.x;
vA.y -= mA * impulse.y;
wA -= iA * Vec2.cross(m_rA, impulse);
vB.x += mB * impulse.x;
vB.y += mB * impulse.y;
wB += iB * Vec2.cross(m_rB, impulse);
pool.pushVec2(2);
}
// data.velocities[m_indexA].v.set(vA);
data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v.set(vB);
data.velocities[m_indexB].w = wB;
pool.pushVec2(1);
}
@Override
public boolean solvePositionConstraints(final SolverData data) {
final Rot qA = pool.popRot();
final Rot qB = pool.popRot();
Vec2 cA = data.positions[m_indexA].c;
float aA = data.positions[m_indexA].a;
Vec2 cB = data.positions[m_indexB].c;
float aB = data.positions[m_indexB].a;
qA.set(aA);
qB.set(aB);
float angularError = 0.0f;
float positionError = 0.0f;
boolean fixedRotation = (m_invIA + m_invIB == 0.0f);
// Solve angular limit constraint.
if (m_enableLimit && m_limitState != LimitState.INACTIVE && fixedRotation == false) {
float angle = aB - aA - m_referenceAngle;
float limitImpulse = 0.0f;
if (m_limitState == LimitState.EQUAL) {
// Prevent large angular corrections
float C =
MathUtils.clamp(angle - m_lowerAngle, -Settings.maxAngularCorrection,
Settings.maxAngularCorrection);
limitImpulse = -m_motorMass * C;
angularError = MathUtils.abs(C);
} else if (m_limitState == LimitState.AT_LOWER) {
float C = angle - m_lowerAngle;
angularError = -C;
// Prevent large angular corrections and allow some slop.
C = MathUtils.clamp(C + Settings.angularSlop, -Settings.maxAngularCorrection, 0.0f);
limitImpulse = -m_motorMass * C;
} else if (m_limitState == LimitState.AT_UPPER) {
float C = angle - m_upperAngle;
angularError = C;
// Prevent large angular corrections and allow some slop.
C = MathUtils.clamp(C - Settings.angularSlop, 0.0f, Settings.maxAngularCorrection);
limitImpulse = -m_motorMass * C;
}
aA -= m_invIA * limitImpulse;
aB += m_invIB * limitImpulse;
}
// Solve point-to-point constraint.
{
qA.set(aA);
qB.set(aB);
final Vec2 rA = pool.popVec2();
final Vec2 rB = pool.popVec2();
final Vec2 C = pool.popVec2();
final Vec2 impulse = pool.popVec2();
Rot.mulToOutUnsafe(qA, C.set(m_localAnchorA).subLocal(m_localCenterA), rA);
Rot.mulToOutUnsafe(qB, C.set(m_localAnchorB).subLocal(m_localCenterB), rB);
C.set(cB).addLocal(rB).subLocal(cA).subLocal(rA);
positionError = C.length();
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 * rA.y * rA.y + iB * rB.y * rB.y;
K.ex.y = -iA * rA.x * rA.y - iB * rB.x * rB.y;
K.ey.x = K.ex.y;
K.ey.y = mA + mB + iA * rA.x * rA.x + iB * rB.x * rB.x;
K.solveToOut(C, impulse);
impulse.negateLocal();
cA.x -= mA * impulse.x;
cA.y -= mA * impulse.y;
aA -= iA * Vec2.cross(rA, impulse);
cB.x += mB * impulse.x;
cB.y += mB * impulse.y;
aB += iB * Vec2.cross(rB, impulse);
pool.pushVec2(4);
pool.pushMat22(1);
}
// data.positions[m_indexA].c.set(cA);
data.positions[m_indexA].a = aA;
// data.positions[m_indexB].c.set(cB);
data.positions[m_indexB].a = aB;
pool.pushRot(2);
return positionError <= Settings.linearSlop && angularError <= Settings.angularSlop;
}
public Vec2 getLocalAnchorA() {
return m_localAnchorA;
}
public Vec2 getLocalAnchorB() {
return m_localAnchorB;
}
public float getReferenceAngle() {
return m_referenceAngle;
}
@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_impulse.x, m_impulse.y).mulLocal(inv_dt);
}
@Override
public float getReactionTorque(float inv_dt) {
return inv_dt * m_impulse.z;
}
public float getJointAngle() {
final Body b1 = m_bodyA;
final Body b2 = m_bodyB;
return b2.m_sweep.a - b1.m_sweep.a - m_referenceAngle;
}
public float getJointSpeed() {
final Body b1 = m_bodyA;
final Body b2 = m_bodyB;
return b2.m_angularVelocity - b1.m_angularVelocity;
}
public boolean isMotorEnabled() {
return m_enableMotor;
}
public void enableMotor(boolean flag) {
m_bodyA.setAwake(true);
m_bodyB.setAwake(true);
m_enableMotor = flag;
}
public float getMotorTorque(float inv_dt) {
return m_motorImpulse * inv_dt;
}
public void setMotorSpeed(final float speed) {
m_bodyA.setAwake(true);
m_bodyB.setAwake(true);
m_motorSpeed = speed;
}
public void setMaxMotorTorque(final float torque) {
m_bodyA.setAwake(true);
m_bodyB.setAwake(true);
m_maxMotorTorque = torque;
}
public float getMotorSpeed() {
return m_motorSpeed;
}
public float getMaxMotorTorque() {
return m_maxMotorTorque;
}
public boolean isLimitEnabled() {
return m_enableLimit;
}
public void enableLimit(final boolean flag) {
if (flag != m_enableLimit) {
m_bodyA.setAwake(true);
m_bodyB.setAwake(true);
m_enableLimit = flag;
m_impulse.z = 0.0f;
}
}
public float getLowerLimit() {
return m_lowerAngle;
}
public float getUpperLimit() {
return m_upperAngle;
}
public void setLimits(final float lower, final float upper) {
assert (lower <= upper);
if (lower != m_lowerAngle || upper != m_upperAngle) {
m_bodyA.setAwake(true);
m_bodyB.setAwake(true);
m_impulse.z = 0.0f;
m_lowerAngle = lower;
m_upperAngle = upper;
}
}
}