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Magic_Game/3rd-party/box2d/Box2D/Dynamics/Contacts/b2ContactSolver.cpp

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/*
* 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;
}
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