*init

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diff --git a/ThirdParty/Box2D/Dynamics/Contacts/b2ContactSolver.cpp b/ThirdParty/Box2D/Dynamics/Contacts/b2ContactSolver.cpp
new file mode 100644
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+++ b/ThirdParty/Box2D/Dynamics/Contacts/b2ContactSolver.cpp
@@ -0,0 +1,838 @@
+/*
+* Copyright (c) 2006-2011 Erin Catto http://www.box2d.org
+*
+* This software is provided 'as-is', without any express or implied
+* warranty.  In no event will the authors be held liable for any damages
+* arising from the use of this software.
+* Permission is granted to anyone to use this software for any purpose,
+* including commercial applications, and to alter it and redistribute it
+* freely, subject to the following restrictions:
+* 1. The origin of this software must not be misrepresented; you must not
+* claim that you wrote the original software. If you use this software
+* in a product, an acknowledgment in the product documentation would be
+* appreciated but is not required.
+* 2. Altered source versions must be plainly marked as such, and must not be
+* misrepresented as being the original software.
+* 3. This notice may not be removed or altered from any source distribution.
+*/
+
+#include "Box2D/Dynamics/Contacts/b2ContactSolver.h"
+
+#include "Box2D/Dynamics/Contacts/b2Contact.h"
+#include "Box2D/Dynamics/b2Body.h"
+#include "Box2D/Dynamics/b2Fixture.h"
+#include "Box2D/Dynamics/b2World.h"
+#include "Box2D/Common/b2StackAllocator.h"
+
+// Solver debugging is normally disabled because the block solver sometimes has to deal with a poorly conditioned effective mass matrix.
+#define B2_DEBUG_SOLVER 0
+
+bool g_blockSolve = true;
+
+struct b2ContactPositionConstraint
+{
+	b2Vec2 localPoints[b2_maxManifoldPoints];
+	b2Vec2 localNormal;
+	b2Vec2 localPoint;
+	int32 indexA;
+	int32 indexB;
+	float32 invMassA, invMassB;
+	b2Vec2 localCenterA, localCenterB;
+	float32 invIA, invIB;
+	b2Manifold::Type type;
+	float32 radiusA, radiusB;
+	int32 pointCount;
+};
+
+b2ContactSolver::b2ContactSolver(b2ContactSolverDef* def)
+{
+	m_step = def->step;
+	m_allocator = def->allocator;
+	m_count = def->count;
+	m_positionConstraints = (b2ContactPositionConstraint*)m_allocator->Allocate(m_count * sizeof(b2ContactPositionConstraint));
+	m_velocityConstraints = (b2ContactVelocityConstraint*)m_allocator->Allocate(m_count * sizeof(b2ContactVelocityConstraint));
+	m_positions = def->positions;
+	m_velocities = def->velocities;
+	m_contacts = def->contacts;
+
+	// Initialize position independent portions of the constraints.
+	for (int32 i = 0; i < m_count; ++i)
+	{
+		b2Contact* contact = m_contacts[i];
+
+		b2Fixture* fixtureA = contact->m_fixtureA;
+		b2Fixture* fixtureB = contact->m_fixtureB;
+		b2Shape* shapeA = fixtureA->GetShape();
+		b2Shape* shapeB = fixtureB->GetShape();
+		float32 radiusA = shapeA->m_radius;
+		float32 radiusB = shapeB->m_radius;
+		b2Body* bodyA = fixtureA->GetBody();
+		b2Body* bodyB = fixtureB->GetBody();
+		b2Manifold* manifold = contact->GetManifold();
+
+		int32 pointCount = manifold->pointCount;
+		b2Assert(pointCount > 0);
+
+		b2ContactVelocityConstraint* vc = m_velocityConstraints + i;
+		vc->friction = contact->m_friction;
+		vc->restitution = contact->m_restitution;
+		vc->tangentSpeed = contact->m_tangentSpeed;
+		vc->indexA = bodyA->m_islandIndex;
+		vc->indexB = bodyB->m_islandIndex;
+		vc->invMassA = bodyA->m_invMass;
+		vc->invMassB = bodyB->m_invMass;
+		vc->invIA = bodyA->m_invI;
+		vc->invIB = bodyB->m_invI;
+		vc->contactIndex = i;
+		vc->pointCount = pointCount;
+		vc->K.SetZero();
+		vc->normalMass.SetZero();
+
+		b2ContactPositionConstraint* pc = m_positionConstraints + i;
+		pc->indexA = bodyA->m_islandIndex;
+		pc->indexB = bodyB->m_islandIndex;
+		pc->invMassA = bodyA->m_invMass;
+		pc->invMassB = bodyB->m_invMass;
+		pc->localCenterA = bodyA->m_sweep.localCenter;
+		pc->localCenterB = bodyB->m_sweep.localCenter;
+		pc->invIA = bodyA->m_invI;
+		pc->invIB = bodyB->m_invI;
+		pc->localNormal = manifold->localNormal;
+		pc->localPoint = manifold->localPoint;
+		pc->pointCount = pointCount;
+		pc->radiusA = radiusA;
+		pc->radiusB = radiusB;
+		pc->type = manifold->type;
+
+		for (int32 j = 0; j < pointCount; ++j)
+		{
+			b2ManifoldPoint* cp = manifold->points + j;
+			b2VelocityConstraintPoint* vcp = vc->points + j;
+	
+			if (m_step.warmStarting)
+			{
+				vcp->normalImpulse = m_step.dtRatio * cp->normalImpulse;
+				vcp->tangentImpulse = m_step.dtRatio * cp->tangentImpulse;
+			}
+			else
+			{
+				vcp->normalImpulse = 0.0f;
+				vcp->tangentImpulse = 0.0f;
+			}
+
+			vcp->rA.SetZero();
+			vcp->rB.SetZero();
+			vcp->normalMass = 0.0f;
+			vcp->tangentMass = 0.0f;
+			vcp->velocityBias = 0.0f;
+
+			pc->localPoints[j] = cp->localPoint;
+		}
+	}
+}
+
+b2ContactSolver::~b2ContactSolver()
+{
+	m_allocator->Free(m_velocityConstraints);
+	m_allocator->Free(m_positionConstraints);
+}
+
+// Initialize position dependent portions of the velocity constraints.
+void b2ContactSolver::InitializeVelocityConstraints()
+{
+	for (int32 i = 0; i < m_count; ++i)
+	{
+		b2ContactVelocityConstraint* vc = m_velocityConstraints + i;
+		b2ContactPositionConstraint* pc = m_positionConstraints + i;
+
+		float32 radiusA = pc->radiusA;
+		float32 radiusB = pc->radiusB;
+		b2Manifold* manifold = m_contacts[vc->contactIndex]->GetManifold();
+
+		int32 indexA = vc->indexA;
+		int32 indexB = vc->indexB;
+
+		float32 mA = vc->invMassA;
+		float32 mB = vc->invMassB;
+		float32 iA = vc->invIA;
+		float32 iB = vc->invIB;
+		b2Vec2 localCenterA = pc->localCenterA;
+		b2Vec2 localCenterB = pc->localCenterB;
+
+		b2Vec2 cA = m_positions[indexA].c;
+		float32 aA = m_positions[indexA].a;
+		b2Vec2 vA = m_velocities[indexA].v;
+		float32 wA = m_velocities[indexA].w;
+
+		b2Vec2 cB = m_positions[indexB].c;
+		float32 aB = m_positions[indexB].a;
+		b2Vec2 vB = m_velocities[indexB].v;
+		float32 wB = m_velocities[indexB].w;
+
+		b2Assert(manifold->pointCount > 0);
+
+		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);
+
+		b2WorldManifold worldManifold;
+		worldManifold.Initialize(manifold, xfA, radiusA, xfB, radiusB);
+
+		vc->normal = worldManifold.normal;
+
+		int32 pointCount = vc->pointCount;
+		for (int32 j = 0; j < pointCount; ++j)
+		{
+			b2VelocityConstraintPoint* vcp = vc->points + j;
+
+			vcp->rA = worldManifold.points[j] - cA;
+			vcp->rB = worldManifold.points[j] - cB;
+
+			float32 rnA = b2Cross(vcp->rA, vc->normal);
+			float32 rnB = b2Cross(vcp->rB, vc->normal);
+
+			float32 kNormal = mA + mB + iA * rnA * rnA + iB * rnB * rnB;
+
+			vcp->normalMass = kNormal > 0.0f ? 1.0f / kNormal : 0.0f;
+
+			b2Vec2 tangent = b2Cross(vc->normal, 1.0f);
+
+			float32 rtA = b2Cross(vcp->rA, tangent);
+			float32 rtB = b2Cross(vcp->rB, tangent);
+
+			float32 kTangent = mA + mB + iA * rtA * rtA + iB * rtB * rtB;
+
+			vcp->tangentMass = kTangent > 0.0f ? 1.0f /  kTangent : 0.0f;
+
+			// Setup a velocity bias for restitution.
+			vcp->velocityBias = 0.0f;
+			float32 vRel = b2Dot(vc->normal, vB + b2Cross(wB, vcp->rB) - vA - b2Cross(wA, vcp->rA));
+			if (vRel < -b2_velocityThreshold)
+			{
+				vcp->velocityBias = -vc->restitution * vRel;
+			}
+		}
+
+		// If we have two points, then prepare the block solver.
+		if (vc->pointCount == 2 && g_blockSolve)
+		{
+			b2VelocityConstraintPoint* vcp1 = vc->points + 0;
+			b2VelocityConstraintPoint* vcp2 = vc->points + 1;
+
+			float32 rn1A = b2Cross(vcp1->rA, vc->normal);
+			float32 rn1B = b2Cross(vcp1->rB, vc->normal);
+			float32 rn2A = b2Cross(vcp2->rA, vc->normal);
+			float32 rn2B = b2Cross(vcp2->rB, vc->normal);
+
+			float32 k11 = mA + mB + iA * rn1A * rn1A + iB * rn1B * rn1B;
+			float32 k22 = mA + mB + iA * rn2A * rn2A + iB * rn2B * rn2B;
+			float32 k12 = mA + mB + iA * rn1A * rn2A + iB * rn1B * rn2B;
+
+			// Ensure a reasonable condition number.
+			const float32 k_maxConditionNumber = 1000.0f;
+			if (k11 * k11 < k_maxConditionNumber * (k11 * k22 - k12 * k12))
+			{
+				// K is safe to invert.
+				vc->K.ex.Set(k11, k12);
+				vc->K.ey.Set(k12, k22);
+				vc->normalMass = vc->K.GetInverse();
+			}
+			else
+			{
+				// The constraints are redundant, just use one.
+				// TODO_ERIN use deepest?
+				vc->pointCount = 1;
+			}
+		}
+	}
+}
+
+void b2ContactSolver::WarmStart()
+{
+	// Warm start.
+	for (int32 i = 0; i < m_count; ++i)
+	{
+		b2ContactVelocityConstraint* vc = m_velocityConstraints + i;
+
+		int32 indexA = vc->indexA;
+		int32 indexB = vc->indexB;
+		float32 mA = vc->invMassA;
+		float32 iA = vc->invIA;
+		float32 mB = vc->invMassB;
+		float32 iB = vc->invIB;
+		int32 pointCount = vc->pointCount;
+
+		b2Vec2 vA = m_velocities[indexA].v;
+		float32 wA = m_velocities[indexA].w;
+		b2Vec2 vB = m_velocities[indexB].v;
+		float32 wB = m_velocities[indexB].w;
+
+		b2Vec2 normal = vc->normal;
+		b2Vec2 tangent = b2Cross(normal, 1.0f);
+
+		for (int32 j = 0; j < pointCount; ++j)
+		{
+			b2VelocityConstraintPoint* vcp = vc->points + j;
+			b2Vec2 P = vcp->normalImpulse * normal + vcp->tangentImpulse * tangent;
+			wA -= iA * b2Cross(vcp->rA, P);
+			vA -= mA * P;
+			wB += iB * b2Cross(vcp->rB, P);
+			vB += mB * P;
+		}
+
+		m_velocities[indexA].v = vA;
+		m_velocities[indexA].w = wA;
+		m_velocities[indexB].v = vB;
+		m_velocities[indexB].w = wB;
+	}
+}
+
+void b2ContactSolver::SolveVelocityConstraints()
+{
+	for (int32 i = 0; i < m_count; ++i)
+	{
+		b2ContactVelocityConstraint* vc = m_velocityConstraints + i;
+
+		int32 indexA = vc->indexA;
+		int32 indexB = vc->indexB;
+		float32 mA = vc->invMassA;
+		float32 iA = vc->invIA;
+		float32 mB = vc->invMassB;
+		float32 iB = vc->invIB;
+		int32 pointCount = vc->pointCount;
+
+		b2Vec2 vA = m_velocities[indexA].v;
+		float32 wA = m_velocities[indexA].w;
+		b2Vec2 vB = m_velocities[indexB].v;
+		float32 wB = m_velocities[indexB].w;
+
+		b2Vec2 normal = vc->normal;
+		b2Vec2 tangent = b2Cross(normal, 1.0f);
+		float32 friction = vc->friction;
+
+		b2Assert(pointCount == 1 || pointCount == 2);
+
+		// Solve tangent constraints first because non-penetration is more important
+		// than friction.
+		for (int32 j = 0; j < pointCount; ++j)
+		{
+			b2VelocityConstraintPoint* vcp = vc->points + j;
+
+			// Relative velocity at contact
+			b2Vec2 dv = vB + b2Cross(wB, vcp->rB) - vA - b2Cross(wA, vcp->rA);
+
+			// Compute tangent force
+			float32 vt = b2Dot(dv, tangent) - vc->tangentSpeed;
+			float32 lambda = vcp->tangentMass * (-vt);
+
+			// b2Clamp the accumulated force
+			float32 maxFriction = friction * vcp->normalImpulse;
+			float32 newImpulse = b2Clamp(vcp->tangentImpulse + lambda, -maxFriction, maxFriction);
+			lambda = newImpulse - vcp->tangentImpulse;
+			vcp->tangentImpulse = newImpulse;
+
+			// Apply contact impulse
+			b2Vec2 P = lambda * tangent;
+
+			vA -= mA * P;
+			wA -= iA * b2Cross(vcp->rA, P);
+
+			vB += mB * P;
+			wB += iB * b2Cross(vcp->rB, P);
+		}
+
+		// Solve normal constraints
+		if (pointCount == 1 || g_blockSolve == false)
+		{
+			for (int32 j = 0; j < pointCount; ++j)
+			{
+				b2VelocityConstraintPoint* vcp = vc->points + j;
+
+				// Relative velocity at contact
+				b2Vec2 dv = vB + b2Cross(wB, vcp->rB) - vA - b2Cross(wA, vcp->rA);
+
+				// Compute normal impulse
+				float32 vn = b2Dot(dv, normal);
+				float32 lambda = -vcp->normalMass * (vn - vcp->velocityBias);
+
+				// b2Clamp the accumulated impulse
+				float32 newImpulse = b2Max(vcp->normalImpulse + lambda, 0.0f);
+				lambda = newImpulse - vcp->normalImpulse;
+				vcp->normalImpulse = newImpulse;
+
+				// Apply contact impulse
+				b2Vec2 P = lambda * normal;
+				vA -= mA * P;
+				wA -= iA * b2Cross(vcp->rA, P);
+
+				vB += mB * P;
+				wB += iB * b2Cross(vcp->rB, P);
+			}
+		}
+		else
+		{
+			// Block solver developed in collaboration with Dirk Gregorius (back in 01/07 on Box2D_Lite).
+			// Build the mini LCP for this contact patch
+			//
+			// vn = A * x + b, vn >= 0, x >= 0 and vn_i * x_i = 0 with i = 1..2
+			//
+			// A = J * W * JT and J = ( -n, -r1 x n, n, r2 x n )
+			// b = vn0 - velocityBias
+			//
+			// The system is solved using the "Total enumeration method" (s. Murty). The complementary constraint vn_i * x_i
+			// implies that we must have in any solution either vn_i = 0 or x_i = 0. So for the 2D contact problem the cases
+			// vn1 = 0 and vn2 = 0, x1 = 0 and x2 = 0, x1 = 0 and vn2 = 0, x2 = 0 and vn1 = 0 need to be tested. The first valid
+			// solution that satisfies the problem is chosen.
+			// 
+			// In order to account of the accumulated impulse 'a' (because of the iterative nature of the solver which only requires
+			// that the accumulated impulse is clamped and not the incremental impulse) we change the impulse variable (x_i).
+			//
+			// Substitute:
+			// 
+			// x = a + d
+			// 
+			// a := old total impulse
+			// x := new total impulse
+			// d := incremental impulse 
+			//
+			// For the current iteration we extend the formula for the incremental impulse
+			// to compute the new total impulse:
+			//
+			// vn = A * d + b
+			//    = A * (x - a) + b
+			//    = A * x + b - A * a
+			//    = A * x + b'
+			// b' = b - A * a;
+
+			b2VelocityConstraintPoint* cp1 = vc->points + 0;
+			b2VelocityConstraintPoint* cp2 = vc->points + 1;
+
+			b2Vec2 a(cp1->normalImpulse, cp2->normalImpulse);
+			b2Assert(a.x >= 0.0f && a.y >= 0.0f);
+
+			// Relative velocity at contact
+			b2Vec2 dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA);
+			b2Vec2 dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA);
+
+			// Compute normal velocity
+			float32 vn1 = b2Dot(dv1, normal);
+			float32 vn2 = b2Dot(dv2, normal);
+
+			b2Vec2 b;
+			b.x = vn1 - cp1->velocityBias;
+			b.y = vn2 - cp2->velocityBias;
+
+			// Compute b'
+			b -= b2Mul(vc->K, a);
+
+			const float32 k_errorTol = 1e-3f;
+			B2_NOT_USED(k_errorTol);
+
+			for (;;)
+			{
+				//
+				// Case 1: vn = 0
+				//
+				// 0 = A * x + b'
+				//
+				// Solve for x:
+				//
+				// x = - inv(A) * b'
+				//
+				b2Vec2 x = - b2Mul(vc->normalMass, b);
+
+				if (x.x >= 0.0f && x.y >= 0.0f)
+				{
+					// Get the incremental impulse
+					b2Vec2 d = x - a;
+
+					// Apply incremental impulse
+					b2Vec2 P1 = d.x * normal;
+					b2Vec2 P2 = d.y * normal;
+					vA -= mA * (P1 + P2);
+					wA -= iA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));
+
+					vB += mB * (P1 + P2);
+					wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));
+
+					// Accumulate
+					cp1->normalImpulse = x.x;
+					cp2->normalImpulse = x.y;
+
+#if B2_DEBUG_SOLVER == 1
+					// Postconditions
+					dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA);
+					dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA);
+
+					// Compute normal velocity
+					vn1 = b2Dot(dv1, normal);
+					vn2 = b2Dot(dv2, normal);
+
+					b2Assert(b2Abs(vn1 - cp1->velocityBias) < k_errorTol);
+					b2Assert(b2Abs(vn2 - cp2->velocityBias) < k_errorTol);
+#endif
+					break;
+				}
+
+				//
+				// Case 2: vn1 = 0 and x2 = 0
+				//
+				//   0 = a11 * x1 + a12 * 0 + b1' 
+				// vn2 = a21 * x1 + a22 * 0 + b2'
+				//
+				x.x = - cp1->normalMass * b.x;
+				x.y = 0.0f;
+				vn1 = 0.0f;
+				vn2 = vc->K.ex.y * x.x + b.y;
+				if (x.x >= 0.0f && vn2 >= 0.0f)
+				{
+					// Get the incremental impulse
+					b2Vec2 d = x - a;
+
+					// Apply incremental impulse
+					b2Vec2 P1 = d.x * normal;
+					b2Vec2 P2 = d.y * normal;
+					vA -= mA * (P1 + P2);
+					wA -= iA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));
+
+					vB += mB * (P1 + P2);
+					wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));
+
+					// Accumulate
+					cp1->normalImpulse = x.x;
+					cp2->normalImpulse = x.y;
+
+#if B2_DEBUG_SOLVER == 1
+					// Postconditions
+					dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA);
+
+					// Compute normal velocity
+					vn1 = b2Dot(dv1, normal);
+
+					b2Assert(b2Abs(vn1 - cp1->velocityBias) < k_errorTol);
+#endif
+					break;
+				}
+
+
+				//
+				// Case 3: vn2 = 0 and x1 = 0
+				//
+				// vn1 = a11 * 0 + a12 * x2 + b1' 
+				//   0 = a21 * 0 + a22 * x2 + b2'
+				//
+				x.x = 0.0f;
+				x.y = - cp2->normalMass * b.y;
+				vn1 = vc->K.ey.x * x.y + b.x;
+				vn2 = 0.0f;
+
+				if (x.y >= 0.0f && vn1 >= 0.0f)
+				{
+					// Resubstitute for the incremental impulse
+					b2Vec2 d = x - a;
+
+					// Apply incremental impulse
+					b2Vec2 P1 = d.x * normal;
+					b2Vec2 P2 = d.y * normal;
+					vA -= mA * (P1 + P2);
+					wA -= iA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));
+
+					vB += mB * (P1 + P2);
+					wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));
+
+					// Accumulate
+					cp1->normalImpulse = x.x;
+					cp2->normalImpulse = x.y;
+
+#if B2_DEBUG_SOLVER == 1
+					// Postconditions
+					dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA);
+
+					// Compute normal velocity
+					vn2 = b2Dot(dv2, normal);
+
+					b2Assert(b2Abs(vn2 - cp2->velocityBias) < k_errorTol);
+#endif
+					break;
+				}
+
+				//
+				// Case 4: x1 = 0 and x2 = 0
+				// 
+				// vn1 = b1
+				// vn2 = b2;
+				x.x = 0.0f;
+				x.y = 0.0f;
+				vn1 = b.x;
+				vn2 = b.y;
+
+				if (vn1 >= 0.0f && vn2 >= 0.0f )
+				{
+					// Resubstitute for the incremental impulse
+					b2Vec2 d = x - a;
+
+					// Apply incremental impulse
+					b2Vec2 P1 = d.x * normal;
+					b2Vec2 P2 = d.y * normal;
+					vA -= mA * (P1 + P2);
+					wA -= iA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));
+
+					vB += mB * (P1 + P2);
+					wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));
+
+					// Accumulate
+					cp1->normalImpulse = x.x;
+					cp2->normalImpulse = x.y;
+
+					break;
+				}
+
+				// No solution, give up. This is hit sometimes, but it doesn't seem to matter.
+				break;
+			}
+		}
+
+		m_velocities[indexA].v = vA;
+		m_velocities[indexA].w = wA;
+		m_velocities[indexB].v = vB;
+		m_velocities[indexB].w = wB;
+	}
+}
+
+void b2ContactSolver::StoreImpulses()
+{
+	for (int32 i = 0; i < m_count; ++i)
+	{
+		b2ContactVelocityConstraint* vc = m_velocityConstraints + i;
+		b2Manifold* manifold = m_contacts[vc->contactIndex]->GetManifold();
+
+		for (int32 j = 0; j < vc->pointCount; ++j)
+		{
+			manifold->points[j].normalImpulse = vc->points[j].normalImpulse;
+			manifold->points[j].tangentImpulse = vc->points[j].tangentImpulse;
+		}
+	}
+}
+
+struct b2PositionSolverManifold
+{
+	void Initialize(b2ContactPositionConstraint* pc, const b2Transform& xfA, const b2Transform& xfB, int32 index)
+	{
+		b2Assert(pc->pointCount > 0);
+
+		switch (pc->type)
+		{
+		case b2Manifold::e_circles:
+			{
+				b2Vec2 pointA = b2Mul(xfA, pc->localPoint);
+				b2Vec2 pointB = b2Mul(xfB, pc->localPoints[0]);
+				normal = pointB - pointA;
+				normal.Normalize();
+				point = 0.5f * (pointA + pointB);
+				separation = b2Dot(pointB - pointA, normal) - pc->radiusA - pc->radiusB;
+			}
+			break;
+
+		case b2Manifold::e_faceA:
+			{
+				normal = b2Mul(xfA.q, pc->localNormal);
+				b2Vec2 planePoint = b2Mul(xfA, pc->localPoint);
+
+				b2Vec2 clipPoint = b2Mul(xfB, pc->localPoints[index]);
+				separation = b2Dot(clipPoint - planePoint, normal) - pc->radiusA - pc->radiusB;
+				point = clipPoint;
+			}
+			break;
+
+		case b2Manifold::e_faceB:
+			{
+				normal = b2Mul(xfB.q, pc->localNormal);
+				b2Vec2 planePoint = b2Mul(xfB, pc->localPoint);
+
+				b2Vec2 clipPoint = b2Mul(xfA, pc->localPoints[index]);
+				separation = b2Dot(clipPoint - planePoint, normal) - pc->radiusA - pc->radiusB;
+				point = clipPoint;
+
+				// Ensure normal points from A to B
+				normal = -normal;
+			}
+			break;
+		}
+	}
+
+	b2Vec2 normal;
+	b2Vec2 point;
+	float32 separation;
+};
+
+// Sequential solver.
+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;
+}
+
+// Sequential position solver for position constraints.
+bool b2ContactSolver::SolveTOIPositionConstraints(int32 toiIndexA, int32 toiIndexB)
+{
+	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;
+		b2Vec2 localCenterB = pc->localCenterB;
+		int32 pointCount = pc->pointCount;
+
+		float32 mA = 0.0f;
+		float32 iA = 0.0f;
+		if (indexA == toiIndexA || indexA == toiIndexB)
+		{
+			mA = pc->invMassA;
+			iA = pc->invIA;
+		}
+
+		float32 mB = 0.0f;
+		float32 iB = 0.;
+		if (indexB == toiIndexA || indexB == toiIndexB)
+		{
+			mB = pc->invMassB;
+			iB = pc->invIB;
+		}
+
+		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_toiBaugarte * (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 >= -1.5f * b2_linearSlop;
+}