bool b2ContactSolver::SolvePositionConstraints()

in Box2D/Dynamics/Contacts/b2ContactSolver.cpp [666:742]

• 52 lines of code
• 4 McCabe index (conditional complexity)

bool b2ContactSolver::SolvePositionConstraints()
{
	float32 minSeparation = 0.0f;

	for (int32 i = 0; i < m_count; ++i)
	{
		b2ContactPositionConstraint* pc = m_positionConstraints + i;

		int32 indexA = pc->indexA;
		int32 indexB = pc->indexB;
		b2Vec2 localCenterA = pc->localCenterA;
		float32 mA = pc->invMassA;
		float32 iA = pc->invIA;
		b2Vec2 localCenterB = pc->localCenterB;
		float32 mB = pc->invMassB;
		float32 iB = pc->invIB;
		int32 pointCount = pc->pointCount;

		b2Vec2 cA = m_positions[indexA].c;
		float32 aA = m_positions[indexA].a;

		b2Vec2 cB = m_positions[indexB].c;
		float32 aB = m_positions[indexB].a;

		// Solve normal constraints
		for (int32 j = 0; j < pointCount; ++j)
		{
			b2Transform xfA, xfB;
			xfA.q.Set(aA);
			xfB.q.Set(aB);
			xfA.p = cA - b2Mul(xfA.q, localCenterA);
			xfB.p = cB - b2Mul(xfB.q, localCenterB);

			b2PositionSolverManifold psm;
			psm.Initialize(pc, xfA, xfB, j);
			b2Vec2 normal = psm.normal;

			b2Vec2 point = psm.point;
			float32 separation = psm.separation;

			b2Vec2 rA = point - cA;
			b2Vec2 rB = point - cB;

			// Track max constraint error.
			minSeparation = b2Min(minSeparation, separation);

			// Prevent large corrections and allow slop.
			float32 C = b2Clamp(b2_baumgarte * (separation + b2_linearSlop), -b2_maxLinearCorrection, 0.0f);

			// Compute the effective mass.
			float32 rnA = b2Cross(rA, normal);
			float32 rnB = b2Cross(rB, normal);
			float32 K = mA + mB + iA * rnA * rnA + iB * rnB * rnB;

			// Compute normal impulse
			float32 impulse = K > 0.0f ? - C / K : 0.0f;

			b2Vec2 P = impulse * normal;

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

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

		m_positions[indexA].c = cA;
		m_positions[indexA].a = aA;

		m_positions[indexB].c = cB;
		m_positions[indexB].a = aB;
	}

	// We can't expect minSpeparation >= -b2_linearSlop because we don't
	// push the separation above -b2_linearSlop.
	return minSeparation >= -3.0f * b2_linearSlop;
}