public override 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;
// Vec2 cA = data.positions[m_indexA].c;
double aA = data.positions[m_indexA].a;
Vec2 vA = data.velocities[m_indexA].v;
double wA = data.velocities[m_indexA].w;
// Vec2 cB = data.positions[m_indexB].c;
double aB = data.positions[m_indexB].a;
Vec2 vB = data.velocities[m_indexB].v;
double wB = data.velocities[m_indexB].w;
Rot qA = pool.popRot();
Rot qB = pool.popRot();
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]
double mA = m_invMassA, mB = m_invMassB;
double iA = m_invIA, iB = m_invIB;
Mat33 K = pool.popMat33();
K.ex.x = mA + mB + m_rA.y * m_rA.y * iA + m_rB.y * m_rB.y * iB;
K.ey.x = -m_rA.y * m_rA.x * iA - m_rB.y * m_rB.x * iB;
K.ez.x = -m_rA.y * iA - m_rB.y * iB;
K.ex.y = K.ey.x;
K.ey.y = mA + mB + m_rA.x * m_rA.x * iA + m_rB.x * m_rB.x * iB;
K.ez.y = m_rA.x * iA + m_rB.x * iB;
K.ex.z = K.ez.x;
K.ey.z = K.ez.y;
K.ez.z = iA + iB;
if (m_frequencyHz > 0.0d)
{
K.getInverse22(m_mass);
double invM = iA + iB;
double m = invM > 0.0d ? 1.0d / invM : 0.0d;
double C = aB - aA - m_referenceAngle;
// Frequency
double omega = 2.0d * MathUtils.PI * m_frequencyHz;
// Damping coefficient
double d = 2.0d * m * m_dampingRatio * omega;
// Spring stiffness
double k = m * omega * omega;
// magic formulas
double h = data.step.dt;
m_gamma = h * (d + h * k);
m_gamma = m_gamma != 0.0d ? 1.0d / m_gamma : 0.0d;
m_bias = C * h * k * m_gamma;
invM += m_gamma;
m_mass.ez.z = invM != 0.0d ? 1.0d / invM : 0.0d;
}
else
{
K.getSymInverse33(m_mass);
m_gamma = 0.0d;
m_bias = 0.0d;
}
if (data.step.warmStarting)
{
Vec2 P = pool.popVec2();
// Scale impulses to support a variable time step.
m_impulse.mulLocal(data.step.dtRatio);
P.set(m_impulse.x, m_impulse.y);
vA.x -= mA * P.x;
vA.y -= mA * P.y;
wA -= iA * (Vec2.cross(m_rA, P) + m_impulse.z);
vB.x += mB * P.x;
vB.y += mB * P.y;
wB += iB * (Vec2.cross(m_rB, P) + m_impulse.z);
pool.pushVec2(1);
}
else
{
m_impulse.setZero();
}
// 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);
pool.pushMat33(1);
}
