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;
//Point-to-point constraint
//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)
//Angle constraint
//Cdot = w2 - w1
//J = [0 0 -1 0 0 1]
//K = invI1 + invI2
/**
* A motor joint is used to control the relative motion between two bodies. A typical usage is to
* control the movement of a dynamic body with respect to the ground.
*
* @author dmurph
*/
public class MotorJoint extends Joint {
// Solver shared
private final Vec2 m_linearOffset = new Vec2();
private float m_angularOffset;
private final Vec2 m_linearImpulse = new Vec2();
private float m_angularImpulse;
private float m_maxForce;
private float m_maxTorque;
private float m_correctionFactor;
// 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 final Vec2 m_linearError = new Vec2();
private float m_angularError;
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;
public MotorJoint(IWorldPool pool, MotorJointDef def) {
super(pool, def);
m_linearOffset.set(def.linearOffset);
m_angularOffset = def.angularOffset;
m_angularImpulse = 0.0f;
m_maxForce = def.maxForce;
m_maxTorque = def.maxTorque;
m_correctionFactor = def.correctionFactor;
}
@Override
public void getAnchorA(Vec2 out) {
out.set(m_bodyA.getPosition());
}
@Override
public void getAnchorB(Vec2 out) {
out.set(m_bodyB.getPosition());
}
public void getReactionForce(float inv_dt, Vec2 out) {
out.set(m_linearImpulse).mulLocal(inv_dt);
}
public float getReactionTorque(float inv_dt) {
return m_angularImpulse * inv_dt;
}
public float getCorrectionFactor() {
return m_correctionFactor;
}
public void setCorrectionFactor(float correctionFactor) {
this.m_correctionFactor = correctionFactor;
}
/**
* Set the target linear offset, in frame A, in meters.
*/
public void setLinearOffset(Vec2 linearOffset) {
if (linearOffset.x != m_linearOffset.x || linearOffset.y != m_linearOffset.y) {
m_bodyA.setAwake(true);
m_bodyB.setAwake(true);
m_linearOffset.set(linearOffset);
}
}
/**
* Get the target linear offset, in frame A, in meters.
*/
public void getLinearOffset(Vec2 out) {
out.set(m_linearOffset);
}
/**
* Get the target linear offset, in frame A, in meters. Do not modify.
*/
public Vec2 getLinearOffset() {
return m_linearOffset;
}
/**
* Set the target angular offset, in radians.
*
* @param angularOffset
*/
public void setAngularOffset(float angularOffset) {
if (angularOffset != m_angularOffset) {
m_bodyA.setAwake(true);
m_bodyB.setAwake(true);
m_angularOffset = angularOffset;
}
}
public float getAngularOffset() {
return m_angularOffset;
}
/**
* Set the maximum friction force in N.
*
* @param force
*/
public void setMaxForce(float force) {
assert (force >= 0.0f);
m_maxForce = force;
}
/**
* Get the maximum friction force in N.
*/
public float getMaxForce() {
return m_maxForce;
}
/**
* Set the maximum friction torque in N*m.
*/
public void setMaxTorque(float torque) {
assert (torque >= 0.0f);
m_maxTorque = torque;
}
/**
* Get the maximum friction torque in N*m.
*/
public float getMaxTorque() {
return m_maxTorque;
}
@Override
public void initVelocityConstraints(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;
final Vec2 cA = data.positions[m_indexA].c;
float aA = data.positions[m_indexA].a;
final Vec2 vA = data.velocities[m_indexA].v;
float wA = data.velocities[m_indexA].w;
final Vec2 cB = data.positions[m_indexB].c;
float aB = data.positions[m_indexB].a;
final 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();
Mat22 K = pool.popMat22();
qA.set(aA);
qB.set(aB);
// Compute the effective mass matrix.
// m_rA = b2Mul(qA, -m_localCenterA);
// m_rB = b2Mul(qB, -m_localCenterB);
m_rA.x = qA.c * -m_localCenterA.x - qA.s * -m_localCenterA.y;
m_rA.y = qA.s * -m_localCenterA.x + qA.c * -m_localCenterA.y;
m_rB.x = qB.c * -m_localCenterB.x - qB.s * -m_localCenterB.y;
m_rB.y = qB.s * -m_localCenterB.x + qB.c * -m_localCenterB.y;
// 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;
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;
}
// m_linearError = cB + m_rB - cA - m_rA - b2Mul(qA, m_linearOffset);
Rot.mulToOutUnsafe(qA, m_linearOffset, temp);
m_linearError.x = cB.x + m_rB.x - cA.x - m_rA.x - temp.x;
m_linearError.y = cB.y + m_rB.y - cA.y - m_rA.y - temp.y;
m_angularError = aB - aA - m_angularOffset;
if (data.step.warmStarting) {
// Scale impulses to support a variable time step.
m_linearImpulse.x *= data.step.dtRatio;
m_linearImpulse.y *= data.step.dtRatio;
m_angularImpulse *= data.step.dtRatio;
final Vec2 P = m_linearImpulse;
vA.x -= mA * P.x;
vA.y -= mA * P.y;
wA -= iA * (m_rA.x * P.y - m_rA.y * P.x + m_angularImpulse);
vB.x += mB * P.x;
vB.y += mB * P.y;
wB += iB * (m_rB.x * P.y - m_rB.y * P.x + m_angularImpulse);
} else {
m_linearImpulse.setZero();
m_angularImpulse = 0.0f;
}
pool.pushVec2(1);
pool.pushMat22(1);
pool.pushRot(2);
// data.velocities[m_indexA].v = vA;
data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v = vB;
data.velocities[m_indexB].w = wB;
}
@Override
public void solveVelocityConstraints(SolverData data) {
final Vec2 vA = data.velocities[m_indexA].v;
float wA = data.velocities[m_indexA].w;
final 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;
float inv_h = data.step.inv_dt;
final Vec2 temp = pool.popVec2();
// Solve angular friction
{
float Cdot = wB - wA + inv_h * m_correctionFactor * m_angularError;
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;
}
final Vec2 Cdot = pool.popVec2();
// Solve linear friction
{
// Cdot = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA) + inv_h * m_correctionFactor *
// m_linearError;
Cdot.x =
vB.x + -wB * m_rB.y - vA.x - -wA * m_rA.y + inv_h * m_correctionFactor * m_linearError.x;
Cdot.y =
vB.y + wB * m_rB.x - vA.y - wA * m_rA.x + inv_h * m_correctionFactor * m_linearError.y;
final Vec2 impulse = temp;
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.x = m_linearImpulse.x - oldImpulse.x;
impulse.y = m_linearImpulse.y - oldImpulse.y;
vA.x -= mA * impulse.x;
vA.y -= mA * impulse.y;
wA -= iA * (m_rA.x * impulse.y - m_rA.y * impulse.x);
vB.x += mB * impulse.x;
vB.y += mB * impulse.y;
wB += iB * (m_rB.x * impulse.y - m_rB.y * impulse.x);
}
pool.pushVec2(3);
// 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;
}
@Override
public boolean solvePositionConstraints(SolverData data) {
return true;
}
}