bool b2GearJoint::SolvePositionConstraints()

in Box2D/Dynamics/Joints/b2GearJoint.cpp [271:368]
82 lines of code
4 McCabe index (conditional complexity)

bool b2GearJoint::SolvePositionConstraints(const b2SolverData& data)
{
	b2Vec2 cA = data.positions[m_indexA].c;
	float32 aA = data.positions[m_indexA].a;
	b2Vec2 cB = data.positions[m_indexB].c;
	float32 aB = data.positions[m_indexB].a;
	b2Vec2 cC = data.positions[m_indexC].c;
	float32 aC = data.positions[m_indexC].a;
	b2Vec2 cD = data.positions[m_indexD].c;
	float32 aD = data.positions[m_indexD].a;

	b2Rot qA(aA), qB(aB), qC(aC), qD(aD);

	float32 linearError = 0.0f;

	float32 coordinateA, coordinateB;

	b2Vec2 JvAC, JvBD;
	float32 JwA, JwB, JwC, JwD;
	float32 mass = 0.0f;

	if (m_typeA == e_revoluteJoint)
	{
		JvAC.SetZero();
		JwA = 1.0f;
		JwC = 1.0f;
		mass += m_iA + m_iC;

		coordinateA = aA - aC - m_referenceAngleA;
	}
	else
	{
		b2Vec2 u = b2Mul(qC, m_localAxisC);
		b2Vec2 rC = b2Mul(qC, m_localAnchorC - m_lcC);
		b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_lcA);
		JvAC = u;
		JwC = b2Cross(rC, u);
		JwA = b2Cross(rA, u);
		mass += m_mC + m_mA + m_iC * JwC * JwC + m_iA * JwA * JwA;

		b2Vec2 pC = m_localAnchorC - m_lcC;
		b2Vec2 pA = b2MulT(qC, rA + (cA - cC));
		coordinateA = b2Dot(pA - pC, m_localAxisC);
	}

	if (m_typeB == e_revoluteJoint)
	{
		JvBD.SetZero();
		JwB = m_ratio;
		JwD = m_ratio;
		mass += m_ratio * m_ratio * (m_iB + m_iD);

		coordinateB = aB - aD - m_referenceAngleB;
	}
	else
	{
		b2Vec2 u = b2Mul(qD, m_localAxisD);
		b2Vec2 rD = b2Mul(qD, m_localAnchorD - m_lcD);
		b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_lcB);
		JvBD = m_ratio * u;
		JwD = m_ratio * b2Cross(rD, u);
		JwB = m_ratio * b2Cross(rB, u);
		mass += m_ratio * m_ratio * (m_mD + m_mB) + m_iD * JwD * JwD + m_iB * JwB * JwB;

		b2Vec2 pD = m_localAnchorD - m_lcD;
		b2Vec2 pB = b2MulT(qD, rB + (cB - cD));
		coordinateB = b2Dot(pB - pD, m_localAxisD);
	}

	float32 C = (coordinateA + m_ratio * coordinateB) - m_constant;

	float32 impulse = 0.0f;
	if (mass > 0.0f)
	{
		impulse = -C / mass;
	}

	cA += m_mA * impulse * JvAC;
	aA += m_iA * impulse * JwA;
	cB += m_mB * impulse * JvBD;
	aB += m_iB * impulse * JwB;
	cC -= m_mC * impulse * JvAC;
	aC -= m_iC * impulse * JwC;
	cD -= m_mD * impulse * JvBD;
	aD -= m_iD * impulse * JwD;

	data.positions[m_indexA].c = cA;
	data.positions[m_indexA].a = aA;
	data.positions[m_indexB].c = cB;
	data.positions[m_indexB].a = aB;
	data.positions[m_indexC].c = cC;
	data.positions[m_indexC].a = aC;
	data.positions[m_indexD].c = cD;
	data.positions[m_indexD].a = aD;

	// TODO_ERIN not implemented
	return linearError < b2_linearSlop;
}