mirror of https://github.com/axmolengine/axmol.git
624 lines
18 KiB
C++
624 lines
18 KiB
C++
/*
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* Copyright (c) 2006-2009 Erin Catto http://www.gphysics.com
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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#include <Box2D/Dynamics/Contacts/b2ContactSolver.h>
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#include <Box2D/Dynamics/Contacts/b2Contact.h>
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#include <Box2D/Dynamics/b2Body.h>
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#include <Box2D/Dynamics/b2Fixture.h>
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#include <Box2D/Dynamics/b2World.h>
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#include <Box2D/Common/b2StackAllocator.h>
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#define B2_DEBUG_SOLVER 0
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b2ContactSolver::b2ContactSolver(b2Contact** contacts, int32 contactCount,
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b2StackAllocator* allocator, float32 impulseRatio)
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{
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m_allocator = allocator;
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m_constraintCount = contactCount;
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m_constraints = (b2ContactConstraint*)m_allocator->Allocate(m_constraintCount * sizeof(b2ContactConstraint));
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for (int32 i = 0; i < m_constraintCount; ++i)
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{
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b2Contact* contact = contacts[i];
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b2Fixture* fixtureA = contact->m_fixtureA;
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b2Fixture* fixtureB = contact->m_fixtureB;
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b2Shape* shapeA = fixtureA->GetShape();
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b2Shape* shapeB = fixtureB->GetShape();
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float32 radiusA = shapeA->m_radius;
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float32 radiusB = shapeB->m_radius;
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b2Body* bodyA = fixtureA->GetBody();
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b2Body* bodyB = fixtureB->GetBody();
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b2Manifold* manifold = contact->GetManifold();
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float32 friction = b2MixFriction(fixtureA->GetFriction(), fixtureB->GetFriction());
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float32 restitution = b2MixRestitution(fixtureA->GetRestitution(), fixtureB->GetRestitution());
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b2Vec2 vA = bodyA->m_linearVelocity;
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b2Vec2 vB = bodyB->m_linearVelocity;
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float32 wA = bodyA->m_angularVelocity;
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float32 wB = bodyB->m_angularVelocity;
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b2Assert(manifold->pointCount > 0);
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b2WorldManifold worldManifold;
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worldManifold.Initialize(manifold, bodyA->m_xf, radiusA, bodyB->m_xf, radiusB);
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b2ContactConstraint* cc = m_constraints + i;
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cc->bodyA = bodyA;
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cc->bodyB = bodyB;
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cc->manifold = manifold;
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cc->normal = worldManifold.normal;
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cc->pointCount = manifold->pointCount;
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cc->friction = friction;
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cc->localNormal = manifold->localNormal;
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cc->localPoint = manifold->localPoint;
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cc->radius = radiusA + radiusB;
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cc->type = manifold->type;
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for (int32 j = 0; j < cc->pointCount; ++j)
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{
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b2ManifoldPoint* cp = manifold->points + j;
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b2ContactConstraintPoint* ccp = cc->points + j;
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ccp->normalImpulse = impulseRatio * cp->normalImpulse;
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ccp->tangentImpulse = impulseRatio * cp->tangentImpulse;
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ccp->localPoint = cp->localPoint;
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ccp->rA = worldManifold.points[j] - bodyA->m_sweep.c;
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ccp->rB = worldManifold.points[j] - bodyB->m_sweep.c;
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float32 rnA = b2Cross(ccp->rA, cc->normal);
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float32 rnB = b2Cross(ccp->rB, cc->normal);
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rnA *= rnA;
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rnB *= rnB;
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float32 kNormal = bodyA->m_invMass + bodyB->m_invMass + bodyA->m_invI * rnA + bodyB->m_invI * rnB;
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b2Assert(kNormal > b2_epsilon);
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ccp->normalMass = 1.0f / kNormal;
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b2Vec2 tangent = b2Cross(cc->normal, 1.0f);
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float32 rtA = b2Cross(ccp->rA, tangent);
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float32 rtB = b2Cross(ccp->rB, tangent);
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rtA *= rtA;
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rtB *= rtB;
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float32 kTangent = bodyA->m_invMass + bodyB->m_invMass + bodyA->m_invI * rtA + bodyB->m_invI * rtB;
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b2Assert(kTangent > b2_epsilon);
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ccp->tangentMass = 1.0f / kTangent;
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// Setup a velocity bias for restitution.
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ccp->velocityBias = 0.0f;
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float32 vRel = b2Dot(cc->normal, vB + b2Cross(wB, ccp->rB) - vA - b2Cross(wA, ccp->rA));
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if (vRel < -b2_velocityThreshold)
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{
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ccp->velocityBias = -restitution * vRel;
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}
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}
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// If we have two points, then prepare the block solver.
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if (cc->pointCount == 2)
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{
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b2ContactConstraintPoint* ccp1 = cc->points + 0;
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b2ContactConstraintPoint* ccp2 = cc->points + 1;
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float32 invMassA = bodyA->m_invMass;
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float32 invIA = bodyA->m_invI;
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float32 invMassB = bodyB->m_invMass;
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float32 invIB = bodyB->m_invI;
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float32 rn1A = b2Cross(ccp1->rA, cc->normal);
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float32 rn1B = b2Cross(ccp1->rB, cc->normal);
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float32 rn2A = b2Cross(ccp2->rA, cc->normal);
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float32 rn2B = b2Cross(ccp2->rB, cc->normal);
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float32 k11 = invMassA + invMassB + invIA * rn1A * rn1A + invIB * rn1B * rn1B;
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float32 k22 = invMassA + invMassB + invIA * rn2A * rn2A + invIB * rn2B * rn2B;
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float32 k12 = invMassA + invMassB + invIA * rn1A * rn2A + invIB * rn1B * rn2B;
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// Ensure a reasonable condition number.
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const float32 k_maxConditionNumber = 100.0f;
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if (k11 * k11 < k_maxConditionNumber * (k11 * k22 - k12 * k12))
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{
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// K is safe to invert.
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cc->K.col1.Set(k11, k12);
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cc->K.col2.Set(k12, k22);
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cc->normalMass = cc->K.GetInverse();
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}
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else
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{
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// The constraints are redundant, just use one.
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// TODO_ERIN use deepest?
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cc->pointCount = 1;
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}
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}
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}
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}
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b2ContactSolver::~b2ContactSolver()
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{
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m_allocator->Free(m_constraints);
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}
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void b2ContactSolver::WarmStart()
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{
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// Warm start.
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for (int32 i = 0; i < m_constraintCount; ++i)
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{
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b2ContactConstraint* c = m_constraints + i;
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b2Body* bodyA = c->bodyA;
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b2Body* bodyB = c->bodyB;
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float32 invMassA = bodyA->m_invMass;
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float32 invIA = bodyA->m_invI;
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float32 invMassB = bodyB->m_invMass;
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float32 invIB = bodyB->m_invI;
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b2Vec2 normal = c->normal;
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b2Vec2 tangent = b2Cross(normal, 1.0f);
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for (int32 j = 0; j < c->pointCount; ++j)
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{
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b2ContactConstraintPoint* ccp = c->points + j;
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b2Vec2 P = ccp->normalImpulse * normal + ccp->tangentImpulse * tangent;
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bodyA->m_angularVelocity -= invIA * b2Cross(ccp->rA, P);
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bodyA->m_linearVelocity -= invMassA * P;
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bodyB->m_angularVelocity += invIB * b2Cross(ccp->rB, P);
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bodyB->m_linearVelocity += invMassB * P;
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}
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}
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}
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void b2ContactSolver::SolveVelocityConstraints()
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{
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for (int32 i = 0; i < m_constraintCount; ++i)
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{
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b2ContactConstraint* c = m_constraints + i;
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b2Body* bodyA = c->bodyA;
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b2Body* bodyB = c->bodyB;
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float32 wA = bodyA->m_angularVelocity;
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float32 wB = bodyB->m_angularVelocity;
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b2Vec2 vA = bodyA->m_linearVelocity;
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b2Vec2 vB = bodyB->m_linearVelocity;
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float32 invMassA = bodyA->m_invMass;
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float32 invIA = bodyA->m_invI;
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float32 invMassB = bodyB->m_invMass;
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float32 invIB = bodyB->m_invI;
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b2Vec2 normal = c->normal;
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b2Vec2 tangent = b2Cross(normal, 1.0f);
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float32 friction = c->friction;
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b2Assert(c->pointCount == 1 || c->pointCount == 2);
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// Solve tangent constraints
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for (int32 j = 0; j < c->pointCount; ++j)
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{
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b2ContactConstraintPoint* ccp = c->points + j;
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// Relative velocity at contact
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b2Vec2 dv = vB + b2Cross(wB, ccp->rB) - vA - b2Cross(wA, ccp->rA);
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// Compute tangent force
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float32 vt = b2Dot(dv, tangent);
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float32 lambda = ccp->tangentMass * (-vt);
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// b2Clamp the accumulated force
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float32 maxFriction = friction * ccp->normalImpulse;
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float32 newImpulse = b2Clamp(ccp->tangentImpulse + lambda, -maxFriction, maxFriction);
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lambda = newImpulse - ccp->tangentImpulse;
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// Apply contact impulse
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b2Vec2 P = lambda * tangent;
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vA -= invMassA * P;
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wA -= invIA * b2Cross(ccp->rA, P);
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vB += invMassB * P;
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wB += invIB * b2Cross(ccp->rB, P);
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ccp->tangentImpulse = newImpulse;
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}
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// Solve normal constraints
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if (c->pointCount == 1)
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{
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b2ContactConstraintPoint* ccp = c->points + 0;
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// Relative velocity at contact
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b2Vec2 dv = vB + b2Cross(wB, ccp->rB) - vA - b2Cross(wA, ccp->rA);
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// Compute normal impulse
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float32 vn = b2Dot(dv, normal);
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float32 lambda = -ccp->normalMass * (vn - ccp->velocityBias);
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// b2Clamp the accumulated impulse
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float32 newImpulse = b2Max(ccp->normalImpulse + lambda, 0.0f);
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lambda = newImpulse - ccp->normalImpulse;
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// Apply contact impulse
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b2Vec2 P = lambda * normal;
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vA -= invMassA * P;
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wA -= invIA * b2Cross(ccp->rA, P);
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vB += invMassB * P;
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wB += invIB * b2Cross(ccp->rB, P);
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ccp->normalImpulse = newImpulse;
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}
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else
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{
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// Block solver developed in collaboration with Dirk Gregorius (back in 01/07 on Box2D_Lite).
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// Build the mini LCP for this contact patch
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//
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// vn = A * x + b, vn >= 0, , vn >= 0, x >= 0 and vn_i * x_i = 0 with i = 1..2
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//
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// A = J * W * JT and J = ( -n, -r1 x n, n, r2 x n )
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// b = vn_0 - velocityBias
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//
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// The system is solved using the "Total enumeration method" (s. Murty). The complementary constraint vn_i * x_i
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// implies that we must have in any solution either vn_i = 0 or x_i = 0. So for the 2D contact problem the cases
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// 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
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// solution that satisfies the problem is chosen.
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//
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// In order to account of the accumulated impulse 'a' (because of the iterative nature of the solver which only requires
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// that the accumulated impulse is clamped and not the incremental impulse) we change the impulse variable (x_i).
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//
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// Substitute:
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//
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// x = x' - a
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//
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// Plug into above equation:
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//
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// vn = A * x + b
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// = A * (x' - a) + b
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// = A * x' + b - A * a
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// = A * x' + b'
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// b' = b - A * a;
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b2ContactConstraintPoint* cp1 = c->points + 0;
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b2ContactConstraintPoint* cp2 = c->points + 1;
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b2Vec2 a(cp1->normalImpulse, cp2->normalImpulse);
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b2Assert(a.x >= 0.0f && a.y >= 0.0f);
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// Relative velocity at contact
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b2Vec2 dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA);
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b2Vec2 dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA);
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// Compute normal velocity
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float32 vn1 = b2Dot(dv1, normal);
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float32 vn2 = b2Dot(dv2, normal);
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b2Vec2 b;
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b.x = vn1 - cp1->velocityBias;
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b.y = vn2 - cp2->velocityBias;
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b -= b2Mul(c->K, a);
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const float32 k_errorTol = 1e-3f;
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B2_NOT_USED(k_errorTol);
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for (;;)
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{
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//
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// Case 1: vn = 0
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//
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// 0 = A * x' + b'
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//
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// Solve for x':
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//
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// x' = - inv(A) * b'
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//
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b2Vec2 x = - b2Mul(c->normalMass, b);
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if (x.x >= 0.0f && x.y >= 0.0f)
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{
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// Resubstitute for the incremental impulse
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b2Vec2 d = x - a;
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// Apply incremental impulse
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b2Vec2 P1 = d.x * normal;
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b2Vec2 P2 = d.y * normal;
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vA -= invMassA * (P1 + P2);
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wA -= invIA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));
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vB += invMassB * (P1 + P2);
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wB += invIB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));
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// Accumulate
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cp1->normalImpulse = x.x;
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cp2->normalImpulse = x.y;
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#if B2_DEBUG_SOLVER == 1
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// Postconditions
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dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA);
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dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA);
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// Compute normal velocity
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vn1 = b2Dot(dv1, normal);
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vn2 = b2Dot(dv2, normal);
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b2Assert(b2Abs(vn1 - cp1->velocityBias) < k_errorTol);
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b2Assert(b2Abs(vn2 - cp2->velocityBias) < k_errorTol);
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#endif
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break;
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}
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//
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// Case 2: vn1 = 0 and x2 = 0
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//
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// 0 = a11 * x1' + a12 * 0 + b1'
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// vn2 = a21 * x1' + a22 * 0 + b2'
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//
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x.x = - cp1->normalMass * b.x;
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x.y = 0.0f;
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vn1 = 0.0f;
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vn2 = c->K.col1.y * x.x + b.y;
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if (x.x >= 0.0f && vn2 >= 0.0f)
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{
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// Resubstitute for the incremental impulse
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b2Vec2 d = x - a;
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// Apply incremental impulse
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b2Vec2 P1 = d.x * normal;
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b2Vec2 P2 = d.y * normal;
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vA -= invMassA * (P1 + P2);
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wA -= invIA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));
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vB += invMassB * (P1 + P2);
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wB += invIB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));
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// Accumulate
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cp1->normalImpulse = x.x;
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cp2->normalImpulse = x.y;
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#if B2_DEBUG_SOLVER == 1
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// Postconditions
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dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA);
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// Compute normal velocity
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vn1 = b2Dot(dv1, normal);
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b2Assert(b2Abs(vn1 - cp1->velocityBias) < k_errorTol);
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#endif
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break;
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}
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//
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// Case 3: vn2 = 0 and x1 = 0
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//
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// vn1 = a11 * 0 + a12 * x2' + b1'
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// 0 = a21 * 0 + a22 * x2' + b2'
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//
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x.x = 0.0f;
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x.y = - cp2->normalMass * b.y;
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vn1 = c->K.col2.x * x.y + b.x;
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vn2 = 0.0f;
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if (x.y >= 0.0f && vn1 >= 0.0f)
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{
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// Resubstitute for the incremental impulse
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b2Vec2 d = x - a;
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// Apply incremental impulse
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b2Vec2 P1 = d.x * normal;
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b2Vec2 P2 = d.y * normal;
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vA -= invMassA * (P1 + P2);
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wA -= invIA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));
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vB += invMassB * (P1 + P2);
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wB += invIB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));
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// Accumulate
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cp1->normalImpulse = x.x;
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cp2->normalImpulse = x.y;
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#if B2_DEBUG_SOLVER == 1
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// Postconditions
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dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA);
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// Compute normal velocity
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vn2 = b2Dot(dv2, normal);
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b2Assert(b2Abs(vn2 - cp2->velocityBias) < k_errorTol);
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#endif
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break;
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}
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//
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// Case 4: x1 = 0 and x2 = 0
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//
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// vn1 = b1
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// vn2 = b2;
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|
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 -= invMassA * (P1 + P2);
|
|
wA -= invIA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));
|
|
|
|
vB += invMassB * (P1 + P2);
|
|
wB += invIB * (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;
|
|
}
|
|
}
|
|
|
|
bodyA->m_linearVelocity = vA;
|
|
bodyA->m_angularVelocity = wA;
|
|
bodyB->m_linearVelocity = vB;
|
|
bodyB->m_angularVelocity = wB;
|
|
}
|
|
}
|
|
|
|
void b2ContactSolver::StoreImpulses()
|
|
{
|
|
for (int32 i = 0; i < m_constraintCount; ++i)
|
|
{
|
|
b2ContactConstraint* c = m_constraints + i;
|
|
b2Manifold* m = c->manifold;
|
|
|
|
for (int32 j = 0; j < c->pointCount; ++j)
|
|
{
|
|
m->points[j].normalImpulse = c->points[j].normalImpulse;
|
|
m->points[j].tangentImpulse = c->points[j].tangentImpulse;
|
|
}
|
|
}
|
|
}
|
|
|
|
struct b2PositionSolverManifold
|
|
{
|
|
void Initialize(b2ContactConstraint* cc, int32 index)
|
|
{
|
|
b2Assert(cc->pointCount > 0);
|
|
|
|
switch (cc->type)
|
|
{
|
|
case b2Manifold::e_circles:
|
|
{
|
|
b2Vec2 pointA = cc->bodyA->GetWorldPoint(cc->localPoint);
|
|
b2Vec2 pointB = cc->bodyB->GetWorldPoint(cc->points[0].localPoint);
|
|
if (b2DistanceSquared(pointA, pointB) > b2_epsilon * b2_epsilon)
|
|
{
|
|
normal = pointB - pointA;
|
|
normal.Normalize();
|
|
}
|
|
else
|
|
{
|
|
normal.Set(1.0f, 0.0f);
|
|
}
|
|
|
|
point = 0.5f * (pointA + pointB);
|
|
separation = b2Dot(pointB - pointA, normal) - cc->radius;
|
|
}
|
|
break;
|
|
|
|
case b2Manifold::e_faceA:
|
|
{
|
|
normal = cc->bodyA->GetWorldVector(cc->localNormal);
|
|
b2Vec2 planePoint = cc->bodyA->GetWorldPoint(cc->localPoint);
|
|
|
|
b2Vec2 clipPoint = cc->bodyB->GetWorldPoint(cc->points[index].localPoint);
|
|
separation = b2Dot(clipPoint - planePoint, normal) - cc->radius;
|
|
point = clipPoint;
|
|
}
|
|
break;
|
|
|
|
case b2Manifold::e_faceB:
|
|
{
|
|
normal = cc->bodyB->GetWorldVector(cc->localNormal);
|
|
b2Vec2 planePoint = cc->bodyB->GetWorldPoint(cc->localPoint);
|
|
|
|
b2Vec2 clipPoint = cc->bodyA->GetWorldPoint(cc->points[index].localPoint);
|
|
separation = b2Dot(clipPoint - planePoint, normal) - cc->radius;
|
|
point = clipPoint;
|
|
|
|
// Ensure normal points from A to B
|
|
normal = -normal;
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
|
|
b2Vec2 normal;
|
|
b2Vec2 point;
|
|
float32 separation;
|
|
};
|
|
|
|
// Sequential solver.
|
|
bool b2ContactSolver::SolvePositionConstraints(float32 baumgarte)
|
|
{
|
|
float32 minSeparation = 0.0f;
|
|
|
|
for (int32 i = 0; i < m_constraintCount; ++i)
|
|
{
|
|
b2ContactConstraint* c = m_constraints + i;
|
|
b2Body* bodyA = c->bodyA;
|
|
b2Body* bodyB = c->bodyB;
|
|
|
|
float32 invMassA = bodyA->m_mass * bodyA->m_invMass;
|
|
float32 invIA = bodyA->m_mass * bodyA->m_invI;
|
|
float32 invMassB = bodyB->m_mass * bodyB->m_invMass;
|
|
float32 invIB = bodyB->m_mass * bodyB->m_invI;
|
|
|
|
// Solve normal constraints
|
|
for (int32 j = 0; j < c->pointCount; ++j)
|
|
{
|
|
b2PositionSolverManifold psm;
|
|
psm.Initialize(c, j);
|
|
b2Vec2 normal = psm.normal;
|
|
|
|
b2Vec2 point = psm.point;
|
|
float32 separation = psm.separation;
|
|
|
|
b2Vec2 rA = point - bodyA->m_sweep.c;
|
|
b2Vec2 rB = point - bodyB->m_sweep.c;
|
|
|
|
// Track max constraint error.
|
|
minSeparation = b2Min(minSeparation, separation);
|
|
|
|
// Prevent large corrections and allow slop.
|
|
float32 C = b2Clamp(baumgarte * (separation + b2_linearSlop), -b2_maxLinearCorrection, 0.0f);
|
|
|
|
// Compute the effective mass.
|
|
float32 rnA = b2Cross(rA, normal);
|
|
float32 rnB = b2Cross(rB, normal);
|
|
float32 K = invMassA + invMassB + invIA * rnA * rnA + invIB * rnB * rnB;
|
|
|
|
// Compute normal impulse
|
|
float32 impulse = K > 0.0f ? - C / K : 0.0f;
|
|
|
|
b2Vec2 P = impulse * normal;
|
|
|
|
bodyA->m_sweep.c -= invMassA * P;
|
|
bodyA->m_sweep.a -= invIA * b2Cross(rA, P);
|
|
bodyA->SynchronizeTransform();
|
|
|
|
bodyB->m_sweep.c += invMassB * P;
|
|
bodyB->m_sweep.a += invIB * b2Cross(rB, P);
|
|
bodyB->SynchronizeTransform();
|
|
}
|
|
}
|
|
|
|
// We can't expect minSpeparation >= -b2_linearSlop because we don't
|
|
// push the separation above -b2_linearSlop.
|
|
return minSeparation >= -1.5f * b2_linearSlop;
|
|
}
|