bool b2RevoluteJoint::SolvePositionConstraints()

in Box2D/Dynamics/Joints/b2RevoluteJoint.cpp [291:375]
63 lines of code
8 McCabe index (conditional complexity)

bool b2RevoluteJoint::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;

	b2Rot qA(aA), qB(aB);

	float32 angularError = 0.0f;
	float32 positionError = 0.0f;

	bool fixedRotation = (m_invIA + m_invIB == 0.0f);

	// Solve angular limit constraint.
	if (m_enableLimit && m_limitState != e_inactiveLimit && fixedRotation == false)
	{
		float32 angle = aB - aA - m_referenceAngle;
		float32 limitImpulse = 0.0f;

		if (m_limitState == e_equalLimits)
		{
			// Prevent large angular corrections
			float32 C = b2Clamp(angle - m_lowerAngle, -b2_maxAngularCorrection, b2_maxAngularCorrection);
			limitImpulse = -m_motorMass * C;
			angularError = b2Abs(C);
		}
		else if (m_limitState == e_atLowerLimit)
		{
			float32 C = angle - m_lowerAngle;
			angularError = -C;

			// Prevent large angular corrections and allow some slop.
			C = b2Clamp(C + b2_angularSlop, -b2_maxAngularCorrection, 0.0f);
			limitImpulse = -m_motorMass * C;
		}
		else if (m_limitState == e_atUpperLimit)
		{
			float32 C = angle - m_upperAngle;
			angularError = C;

			// Prevent large angular corrections and allow some slop.
			C = b2Clamp(C - b2_angularSlop, 0.0f, b2_maxAngularCorrection);
			limitImpulse = -m_motorMass * C;
		}

		aA -= m_invIA * limitImpulse;
		aB += m_invIB * limitImpulse;
	}

	// Solve point-to-point constraint.
	{
		qA.Set(aA);
		qB.Set(aB);
		b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
		b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB);

		b2Vec2 C = cB + rB - cA - rA;
		positionError = C.Length();

		float32 mA = m_invMassA, mB = m_invMassB;
		float32 iA = m_invIA, iB = m_invIB;

		b2Mat22 K;
		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;

		b2Vec2 impulse = -K.Solve(C);

		cA -= mA * impulse;
		aA -= iA * b2Cross(rA, impulse);

		cB += mB * impulse;
		aB += iB * b2Cross(rB, impulse);
	}

	data.positions[m_indexA].c = cA;
	data.positions[m_indexA].a = aA;
	data.positions[m_indexB].c = cB;
	data.positions[m_indexB].a = aB;
	
	return positionError <= b2_linearSlop && angularError <= b2_angularSlop;
}