btMultiBodyDynamicsWorld.cpp

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/*
Bullet Continuous Collision Detection and Physics Library
Copyright (c) 2013 Erwin Coumans  http://bulletphysics.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 "btMultiBodyDynamicsWorld.h"
#include "btMultiBodyConstraintSolver.h"
#include "btMultiBody.h"
#include "btMultiBodyLinkCollider.h"
#include "BulletCollision/CollisionDispatch/btSimulationIslandManager.h"
#include "LinearMath/btQuickprof.h"
#include "btMultiBodyConstraint.h"
#include "LinearMath/btIDebugDraw.h"
#include "LinearMath/btSerializer.h"
 
 
void    btMultiBodyDynamicsWorld::addMultiBody(btMultiBody* body, int group, int mask)
{
        m_multiBodies.push_back(body);
 
}
 
void    btMultiBodyDynamicsWorld::removeMultiBody(btMultiBody* body)
{
        m_multiBodies.remove(body);
}
 
void    btMultiBodyDynamicsWorld::calculateSimulationIslands()
{
        BT_PROFILE("calculateSimulationIslands");
 
        getSimulationIslandManager()->updateActivationState(getCollisionWorld(),getCollisionWorld()->getDispatcher());
 
    {
        //merge islands based on speculative contact manifolds too
        for (int i=0;i<this->m_predictiveManifolds.size();i++)
        {
            btPersistentManifold* manifold = m_predictiveManifolds[i];
            
            const btCollisionObject* colObj0 = manifold->getBody0();
            const btCollisionObject* colObj1 = manifold->getBody1();
            
            if (((colObj0) && (!(colObj0)->isStaticOrKinematicObject())) &&
                ((colObj1) && (!(colObj1)->isStaticOrKinematicObject())))
            {
                                getSimulationIslandManager()->getUnionFind().unite((colObj0)->getIslandTag(),(colObj1)->getIslandTag());
            }
        }
    }
    
        {
                int i;
                int numConstraints = int(m_constraints.size());
                for (i=0;i< numConstraints ; i++ )
                {
                        btTypedConstraint* constraint = m_constraints[i];
                        if (constraint->isEnabled())
                        {
                                const btRigidBody* colObj0 = &constraint->getRigidBodyA();
                                const btRigidBody* colObj1 = &constraint->getRigidBodyB();
 
                                if (((colObj0) && (!(colObj0)->isStaticOrKinematicObject())) &&
                                        ((colObj1) && (!(colObj1)->isStaticOrKinematicObject())))
                                {
                                        getSimulationIslandManager()->getUnionFind().unite((colObj0)->getIslandTag(),(colObj1)->getIslandTag());
                                }
                        }
                }
        }
 
        //merge islands linked by Featherstone link colliders
        for (int i=0;i<m_multiBodies.size();i++)
        {
                btMultiBody* body = m_multiBodies[i];
                {
                        btMultiBodyLinkCollider* prev = body->getBaseCollider();
 
                        for (int b=0;b<body->getNumLinks();b++)
                        {
                                btMultiBodyLinkCollider* cur = body->getLink(b).m_collider;
                                
                                if (((cur) && (!(cur)->isStaticOrKinematicObject())) &&
                                        ((prev) && (!(prev)->isStaticOrKinematicObject())))
                                {
                                        int tagPrev = prev->getIslandTag();
                                        int tagCur = cur->getIslandTag();
                                        getSimulationIslandManager()->getUnionFind().unite(tagPrev, tagCur);
                                }
                                if (cur && !cur->isStaticOrKinematicObject())
                                        prev = cur;
                                
                        }
                }
        }
 
        //merge islands linked by multibody constraints
        {
                for (int i=0;i<this->m_multiBodyConstraints.size();i++)
                {
                        btMultiBodyConstraint* c = m_multiBodyConstraints[i];
                        int tagA = c->getIslandIdA();
                        int tagB = c->getIslandIdB();
                        if (tagA>=0 && tagB>=0)
                                getSimulationIslandManager()->getUnionFind().unite(tagA, tagB);
                }
        }
 
        //Store the island id in each body
        getSimulationIslandManager()->storeIslandActivationState(getCollisionWorld());
 
}
 
 
void    btMultiBodyDynamicsWorld::updateActivationState(btScalar timeStep)
{
        BT_PROFILE("btMultiBodyDynamicsWorld::updateActivationState");
 
        
        
        for ( int i=0;i<m_multiBodies.size();i++)
        {
                btMultiBody* body = m_multiBodies[i];
                if (body)
                {
                        body->checkMotionAndSleepIfRequired(timeStep);
                        if (!body->isAwake())
                        {
                                btMultiBodyLinkCollider* col = body->getBaseCollider();
                                if (col && col->getActivationState() == ACTIVE_TAG)
                                {
                                        col->setActivationState( WANTS_DEACTIVATION);
                                        col->setDeactivationTime(0.f);
                                }
                                for (int b=0;b<body->getNumLinks();b++)
                                {
                                        btMultiBodyLinkCollider* col = body->getLink(b).m_collider;
                                        if (col && col->getActivationState() == ACTIVE_TAG)
                                        {
                                                col->setActivationState( WANTS_DEACTIVATION);
                                                col->setDeactivationTime(0.f);
                                        }
                                }
                        } else
                        {
                                btMultiBodyLinkCollider* col = body->getBaseCollider();
                                if (col && col->getActivationState() != DISABLE_DEACTIVATION)
                                        col->setActivationState( ACTIVE_TAG );
 
                                for (int b=0;b<body->getNumLinks();b++)
                                {
                                        btMultiBodyLinkCollider* col = body->getLink(b).m_collider;
                                        if (col && col->getActivationState() != DISABLE_DEACTIVATION)
                                                col->setActivationState( ACTIVE_TAG );
                                }
                        }
 
                }
        }
 
        btDiscreteDynamicsWorld::updateActivationState(timeStep);
}
 
 
SIMD_FORCE_INLINE       int     btGetConstraintIslandId2(const btTypedConstraint* lhs)
{
        int islandId;
        
        const btCollisionObject& rcolObj0 = lhs->getRigidBodyA();
        const btCollisionObject& rcolObj1 = lhs->getRigidBodyB();
        islandId= rcolObj0.getIslandTag()>=0?rcolObj0.getIslandTag():rcolObj1.getIslandTag();
        return islandId;
 
}
 
 
class btSortConstraintOnIslandPredicate2
{
        public:
 
                bool operator() ( const btTypedConstraint* lhs, const btTypedConstraint* rhs ) const
                {
                        int rIslandId0,lIslandId0;
                        rIslandId0 = btGetConstraintIslandId2(rhs);
                        lIslandId0 = btGetConstraintIslandId2(lhs);
                        return lIslandId0 < rIslandId0;
                }
};
 
 
 
SIMD_FORCE_INLINE       int     btGetMultiBodyConstraintIslandId(const btMultiBodyConstraint* lhs)
{
        int islandId;
        
        int islandTagA = lhs->getIslandIdA();
        int islandTagB = lhs->getIslandIdB();
        islandId= islandTagA>=0?islandTagA:islandTagB;
        return islandId;
 
}
 
 
class btSortMultiBodyConstraintOnIslandPredicate
{
        public:
 
                bool operator() ( const btMultiBodyConstraint* lhs, const btMultiBodyConstraint* rhs ) const
                {
                        int rIslandId0,lIslandId0;
                        rIslandId0 = btGetMultiBodyConstraintIslandId(rhs);
                        lIslandId0 = btGetMultiBodyConstraintIslandId(lhs);
                        return lIslandId0 < rIslandId0;
                }
};
 
struct MultiBodyInplaceSolverIslandCallback : public btSimulationIslandManager::IslandCallback
{
        btContactSolverInfo*    m_solverInfo;
        btMultiBodyConstraintSolver*            m_solver;
        btMultiBodyConstraint**         m_multiBodySortedConstraints;
        int                                                     m_numMultiBodyConstraints;
        
        btTypedConstraint**             m_sortedConstraints;
        int                                             m_numConstraints;
        btIDebugDraw*                   m_debugDrawer;
        btDispatcher*                   m_dispatcher;
        
        btAlignedObjectArray<btCollisionObject*> m_bodies;
        btAlignedObjectArray<btPersistentManifold*> m_manifolds;
        btAlignedObjectArray<btTypedConstraint*> m_constraints;
        btAlignedObjectArray<btMultiBodyConstraint*> m_multiBodyConstraints;
 
 
        MultiBodyInplaceSolverIslandCallback(   btMultiBodyConstraintSolver*    solver,
                                                                        btDispatcher* dispatcher)
                :m_solverInfo(NULL),
                m_solver(solver),
                m_multiBodySortedConstraints(NULL),
                m_numConstraints(0),
                m_debugDrawer(NULL),
                m_dispatcher(dispatcher)
        {
 
        }
 
        MultiBodyInplaceSolverIslandCallback& operator=(MultiBodyInplaceSolverIslandCallback& other)
        {
                btAssert(0);
                (void)other;
                return *this;
        }
 
        SIMD_FORCE_INLINE void setup ( btContactSolverInfo* solverInfo, btTypedConstraint** sortedConstraints, int numConstraints, btMultiBodyConstraint** sortedMultiBodyConstraints,  int     numMultiBodyConstraints,        btIDebugDraw* debugDrawer)
        {
                btAssert(solverInfo);
                m_solverInfo = solverInfo;
 
                m_multiBodySortedConstraints = sortedMultiBodyConstraints;
                m_numMultiBodyConstraints = numMultiBodyConstraints;
                m_sortedConstraints = sortedConstraints;
                m_numConstraints = numConstraints;
 
                m_debugDrawer = debugDrawer;
                m_bodies.resize (0);
                m_manifolds.resize (0);
                m_constraints.resize (0);
                m_multiBodyConstraints.resize(0);
        }
 
        
        virtual void    processIsland(btCollisionObject** bodies,int numBodies,btPersistentManifold**   manifolds,int numManifolds, int islandId)
        {
                if (islandId<0)
                {
                        m_solver->solveMultiBodyGroup( bodies,numBodies,manifolds, numManifolds,m_sortedConstraints, m_numConstraints, &m_multiBodySortedConstraints[0],m_numConstraints,*m_solverInfo,m_debugDrawer,m_dispatcher);
                } else
                {
                                //also add all non-contact constraints/joints for this island
                        btTypedConstraint** startConstraint = 0;
                        btMultiBodyConstraint** startMultiBodyConstraint = 0;
 
                        int numCurConstraints = 0;
                        int numCurMultiBodyConstraints = 0;
 
                        int i;
                        
                        //find the first constraint for this island
 
                        for (i=0;i<m_numConstraints;i++)
                        {
                                if (btGetConstraintIslandId2(m_sortedConstraints[i]) == islandId)
                                {
                                        startConstraint = &m_sortedConstraints[i];
                                        break;
                                }
                        }
                        //count the number of constraints in this island
                        for (;i<m_numConstraints;i++)
                        {
                                if (btGetConstraintIslandId2(m_sortedConstraints[i]) == islandId)
                                {
                                        numCurConstraints++;
                                }
                        }
 
                        for (i=0;i<m_numMultiBodyConstraints;i++)
                        {
                                if (btGetMultiBodyConstraintIslandId(m_multiBodySortedConstraints[i]) == islandId)
                                {
                                        
                                        startMultiBodyConstraint = &m_multiBodySortedConstraints[i];
                                        break;
                                }
                        }
                        //count the number of multi body constraints in this island
                        for (;i<m_numMultiBodyConstraints;i++)
                        {
                                if (btGetMultiBodyConstraintIslandId(m_multiBodySortedConstraints[i]) == islandId)
                                {
                                        numCurMultiBodyConstraints++;
                                }
                        }
 
                        //if (m_solverInfo->m_minimumSolverBatchSize<=1)
                        //{
                        //      m_solver->solveGroup( bodies,numBodies,manifolds, numManifolds,startConstraint,numCurConstraints,*m_solverInfo,m_debugDrawer,m_dispatcher);
                        //} else
                        {
                                
                                for (i=0;i<numBodies;i++)
                                        m_bodies.push_back(bodies[i]);
                                for (i=0;i<numManifolds;i++)
                                        m_manifolds.push_back(manifolds[i]);
                                for (i=0;i<numCurConstraints;i++)
                                        m_constraints.push_back(startConstraint[i]);
                                
                                for (i=0;i<numCurMultiBodyConstraints;i++)
                                        m_multiBodyConstraints.push_back(startMultiBodyConstraint[i]);
                                
                                if ((m_constraints.size()+m_manifolds.size())>m_solverInfo->m_minimumSolverBatchSize)
                                {
                                        processConstraints();
                                } else
                                {
                                        //printf("deferred\n");
                                }
                        }
                }
        }
        void    processConstraints()
        {
 
                btCollisionObject** bodies = m_bodies.size()? &m_bodies[0]:0;
                btPersistentManifold** manifold = m_manifolds.size()?&m_manifolds[0]:0;
                btTypedConstraint** constraints = m_constraints.size()?&m_constraints[0]:0;
                btMultiBodyConstraint** multiBodyConstraints = m_multiBodyConstraints.size() ? &m_multiBodyConstraints[0] : 0;                  
 
                //printf("mb contacts = %d, mb constraints = %d\n", mbContacts, m_multiBodyConstraints.size());
        
                m_solver->solveMultiBodyGroup( bodies,m_bodies.size(),manifold, m_manifolds.size(),constraints, m_constraints.size() ,multiBodyConstraints, m_multiBodyConstraints.size(), *m_solverInfo,m_debugDrawer,m_dispatcher);
                m_bodies.resize(0);
                m_manifolds.resize(0);
                m_constraints.resize(0);
                m_multiBodyConstraints.resize(0);
        }
 
};
 
 
 
btMultiBodyDynamicsWorld::btMultiBodyDynamicsWorld(btDispatcher* dispatcher,btBroadphaseInterface* pairCache,btMultiBodyConstraintSolver* constraintSolver,btCollisionConfiguration* collisionConfiguration)
        :btDiscreteDynamicsWorld(dispatcher,pairCache,constraintSolver,collisionConfiguration),
        m_multiBodyConstraintSolver(constraintSolver)
{
        //split impulse is not yet supported for Featherstone hierarchies
//      getSolverInfo().m_splitImpulse = false;
        getSolverInfo().m_solverMode |=SOLVER_USE_2_FRICTION_DIRECTIONS;
        m_solverMultiBodyIslandCallback = new MultiBodyInplaceSolverIslandCallback(constraintSolver,dispatcher);
}
 
btMultiBodyDynamicsWorld::~btMultiBodyDynamicsWorld ()
{
        delete m_solverMultiBodyIslandCallback;
}
 
void    btMultiBodyDynamicsWorld::forwardKinematics()
{
 
        for (int b=0;b<m_multiBodies.size();b++)
        {
                btMultiBody* bod = m_multiBodies[b];
                bod->forwardKinematics(m_scratch_world_to_local,m_scratch_local_origin);
        }
}
void    btMultiBodyDynamicsWorld::solveConstraints(btContactSolverInfo& solverInfo)
{
        forwardKinematics();
 
 
 
        BT_PROFILE("solveConstraints");
        
        m_sortedConstraints.resize( m_constraints.size());
        int i; 
        for (i=0;i<getNumConstraints();i++)
        {
                m_sortedConstraints[i] = m_constraints[i];
        }
        m_sortedConstraints.quickSort(btSortConstraintOnIslandPredicate2());
        btTypedConstraint** constraintsPtr = getNumConstraints() ? &m_sortedConstraints[0] : 0;
 
        m_sortedMultiBodyConstraints.resize(m_multiBodyConstraints.size());
        for (i=0;i<m_multiBodyConstraints.size();i++)
        {
                m_sortedMultiBodyConstraints[i] = m_multiBodyConstraints[i];
        }
        m_sortedMultiBodyConstraints.quickSort(btSortMultiBodyConstraintOnIslandPredicate());
 
        btMultiBodyConstraint** sortedMultiBodyConstraints = m_sortedMultiBodyConstraints.size() ?  &m_sortedMultiBodyConstraints[0] : 0;
        
 
        m_solverMultiBodyIslandCallback->setup(&solverInfo,constraintsPtr,m_sortedConstraints.size(),sortedMultiBodyConstraints,m_sortedMultiBodyConstraints.size(), getDebugDrawer());
        m_constraintSolver->prepareSolve(getCollisionWorld()->getNumCollisionObjects(), getCollisionWorld()->getDispatcher()->getNumManifolds());
        
        m_islandManager->buildAndProcessIslands(getCollisionWorld()->getDispatcher(),getCollisionWorld(),m_solverMultiBodyIslandCallback);
 
#ifndef BT_USE_VIRTUAL_CLEARFORCES_AND_GRAVITY
        {
                BT_PROFILE("btMultiBody addForce");
                for (int i=0;i<this->m_multiBodies.size();i++)
                {
                        btMultiBody* bod = m_multiBodies[i];
 
                        bool isSleeping = false;
                        
                        if (bod->getBaseCollider() && bod->getBaseCollider()->getActivationState() == ISLAND_SLEEPING)
                        {
                                isSleeping = true;
                        } 
                        for (int b=0;b<bod->getNumLinks();b++)
                        {
                                if (bod->getLink(b).m_collider && bod->getLink(b).m_collider->getActivationState()==ISLAND_SLEEPING)
                                        isSleeping = true;
                        } 
 
                        if (!isSleeping)
                        {
                                //useless? they get resized in stepVelocities once again (AND DIFFERENTLY)
                                m_scratch_r.resize(bod->getNumLinks()+1);                       //multidof? ("Y"s use it and it is used to store qdd)
                                m_scratch_v.resize(bod->getNumLinks()+1);
                                m_scratch_m.resize(bod->getNumLinks()+1);
 
                                bod->addBaseForce(m_gravity * bod->getBaseMass());
 
                                for (int j = 0; j < bod->getNumLinks(); ++j) 
                                {
                                        bod->addLinkForce(j, m_gravity * bod->getLinkMass(j));
                                }
                        }//if (!isSleeping)
                }
        }
#endif //BT_USE_VIRTUAL_CLEARFORCES_AND_GRAVITY
        
 
        {
                BT_PROFILE("btMultiBody stepVelocities");
                for (int i=0;i<this->m_multiBodies.size();i++)
                {
                        btMultiBody* bod = m_multiBodies[i];
 
                        bool isSleeping = false;
                        
                        if (bod->getBaseCollider() && bod->getBaseCollider()->getActivationState() == ISLAND_SLEEPING)
                        {
                                isSleeping = true;
                        } 
                        for (int b=0;b<bod->getNumLinks();b++)
                        {
                                if (bod->getLink(b).m_collider && bod->getLink(b).m_collider->getActivationState()==ISLAND_SLEEPING)
                                        isSleeping = true;
                        } 
 
                        if (!isSleeping)
                        {
                                //useless? they get resized in stepVelocities once again (AND DIFFERENTLY)
                                m_scratch_r.resize(bod->getNumLinks()+1);                       //multidof? ("Y"s use it and it is used to store qdd)
                                m_scratch_v.resize(bod->getNumLinks()+1);
                                m_scratch_m.resize(bod->getNumLinks()+1);
                                bool doNotUpdatePos = false;
 
                                {
                                        if(!bod->isUsingRK4Integration())
                                        {
                                                bod->computeAccelerationsArticulatedBodyAlgorithmMultiDof(solverInfo.m_timeStep, m_scratch_r, m_scratch_v, m_scratch_m);
                                        }
                                        else
                                        {                                               
                                                //
                                                int numDofs = bod->getNumDofs() + 6;
                                                int numPosVars = bod->getNumPosVars() + 7;
                                                btAlignedObjectArray<btScalar> scratch_r2; scratch_r2.resize(2*numPosVars + 8*numDofs);
                                                //convenience
                                                btScalar *pMem = &scratch_r2[0];
                                                btScalar *scratch_q0 = pMem; pMem += numPosVars;
                                                btScalar *scratch_qx = pMem; pMem += numPosVars;
                                                btScalar *scratch_qd0 = pMem; pMem += numDofs;
                                                btScalar *scratch_qd1 = pMem; pMem += numDofs;
                                                btScalar *scratch_qd2 = pMem; pMem += numDofs;
                                                btScalar *scratch_qd3 = pMem; pMem += numDofs;
                                                btScalar *scratch_qdd0 = pMem; pMem += numDofs;
                                                btScalar *scratch_qdd1 = pMem; pMem += numDofs;
                                                btScalar *scratch_qdd2 = pMem; pMem += numDofs;
                                                btScalar *scratch_qdd3 = pMem; pMem += numDofs;
                                                btAssert((pMem - (2*numPosVars + 8*numDofs)) == &scratch_r2[0]);
 
                                                //copy q0 to scratch_q0 and qd0 to scratch_qd0
                                                scratch_q0[0] = bod->getWorldToBaseRot().x();
                                                scratch_q0[1] = bod->getWorldToBaseRot().y();
                                                scratch_q0[2] = bod->getWorldToBaseRot().z();
                                                scratch_q0[3] = bod->getWorldToBaseRot().w();
                                                scratch_q0[4] = bod->getBasePos().x();
                                                scratch_q0[5] = bod->getBasePos().y();
                                                scratch_q0[6] = bod->getBasePos().z();
                                                //
                                                for(int link = 0; link < bod->getNumLinks(); ++link)
                                                {
                                                        for(int dof = 0; dof < bod->getLink(link).m_posVarCount; ++dof)
                                                                scratch_q0[7 + bod->getLink(link).m_cfgOffset + dof] = bod->getLink(link).m_jointPos[dof];                                                      
                                                }
                                                //
                                                for(int dof = 0; dof < numDofs; ++dof)                                                          
                                                        scratch_qd0[dof] = bod->getVelocityVector()[dof];
                                                struct
                                                {
                                                    btMultiBody *bod;
                            btScalar *scratch_qx, *scratch_q0;
 
                                                    void operator()()
                                                    {
                                                        for(int dof = 0; dof < bod->getNumPosVars() + 7; ++dof)
                                    scratch_qx[dof] = scratch_q0[dof];
                                                    }
                                                } pResetQx = {bod, scratch_qx, scratch_q0};
                                                //
                                                struct
                                                {
                                                    void operator()(btScalar dt, const btScalar *pDer, const btScalar *pCurVal, btScalar *pVal, int size)
                                                    {
                                                        for(int i = 0; i < size; ++i)
                                    pVal[i] = pCurVal[i] + dt * pDer[i];
                                                    }
 
                                                } pEulerIntegrate;
                                                //
                                                struct
                        {
                            void operator()(btMultiBody *pBody, const btScalar *pData)
                            {
                                btScalar *pVel = const_cast<btScalar*>(pBody->getVelocityVector());
 
                                for(int i = 0; i < pBody->getNumDofs() + 6; ++i)
                                    pVel[i] = pData[i];
 
                            }
                        } pCopyToVelocityVector;
                                                //
                        struct
                                                {
                                                    void operator()(const btScalar *pSrc, btScalar *pDst, int start, int size)
                                                    {
                                                        for(int i = 0; i < size; ++i)
                                    pDst[i] = pSrc[start + i];
                                                    }
                                                } pCopy;
                                                //
 
                                                btScalar h = solverInfo.m_timeStep;
                                                #define output &m_scratch_r[bod->getNumDofs()]
                                                //calc qdd0 from: q0 & qd0      
                                                bod->computeAccelerationsArticulatedBodyAlgorithmMultiDof(0., m_scratch_r, m_scratch_v, m_scratch_m);
                                                pCopy(output, scratch_qdd0, 0, numDofs);
                                                //calc q1 = q0 + h/2 * qd0
                                                pResetQx();
                                                bod->stepPositionsMultiDof(btScalar(.5)*h, scratch_qx, scratch_qd0);
                                                //calc qd1 = qd0 + h/2 * qdd0
                                                pEulerIntegrate(btScalar(.5)*h, scratch_qdd0, scratch_qd0, scratch_qd1, numDofs);
                                                //
                                                //calc qdd1 from: q1 & qd1
                                                pCopyToVelocityVector(bod, scratch_qd1);
                                                bod->computeAccelerationsArticulatedBodyAlgorithmMultiDof(0., m_scratch_r, m_scratch_v, m_scratch_m);
                                                pCopy(output, scratch_qdd1, 0, numDofs);
                                                //calc q2 = q0 + h/2 * qd1
                                                pResetQx();
                                                bod->stepPositionsMultiDof(btScalar(.5)*h, scratch_qx, scratch_qd1);
                                                //calc qd2 = qd0 + h/2 * qdd1
                                                pEulerIntegrate(btScalar(.5)*h, scratch_qdd1, scratch_qd0, scratch_qd2, numDofs);
                                                //
                                                //calc qdd2 from: q2 & qd2
                                                pCopyToVelocityVector(bod, scratch_qd2);
                                                bod->computeAccelerationsArticulatedBodyAlgorithmMultiDof(0., m_scratch_r, m_scratch_v, m_scratch_m);
                                                pCopy(output, scratch_qdd2, 0, numDofs);
                                                //calc q3 = q0 + h * qd2
                                                pResetQx();
                                                bod->stepPositionsMultiDof(h, scratch_qx, scratch_qd2);
                                                //calc qd3 = qd0 + h * qdd2
                                                pEulerIntegrate(h, scratch_qdd2, scratch_qd0, scratch_qd3, numDofs);
                                                //
                                                //calc qdd3 from: q3 & qd3
                                                pCopyToVelocityVector(bod, scratch_qd3);
                                                bod->computeAccelerationsArticulatedBodyAlgorithmMultiDof(0., m_scratch_r, m_scratch_v, m_scratch_m);
                                                pCopy(output, scratch_qdd3, 0, numDofs);
 
                                                //
                                                //calc q = q0 + h/6(qd0 + 2*(qd1 + qd2) + qd3)
                                                //calc qd = qd0 + h/6(qdd0 + 2*(qdd1 + qdd2) + qdd3)                                            
                                                btAlignedObjectArray<btScalar> delta_q; delta_q.resize(numDofs);
                                                btAlignedObjectArray<btScalar> delta_qd; delta_qd.resize(numDofs);
                                                for(int i = 0; i < numDofs; ++i)
                                                {
                                                        delta_q[i] = h/btScalar(6.)*(scratch_qd0[i] + 2*scratch_qd1[i] + 2*scratch_qd2[i] + scratch_qd3[i]);
                                                        delta_qd[i] = h/btScalar(6.)*(scratch_qdd0[i] + 2*scratch_qdd1[i] + 2*scratch_qdd2[i] + scratch_qdd3[i]);                                                       
                                                        //delta_q[i] = h*scratch_qd0[i];
                                                        //delta_qd[i] = h*scratch_qdd0[i];
                                                }
                                                //
                                                pCopyToVelocityVector(bod, scratch_qd0);
                                                bod->applyDeltaVeeMultiDof(&delta_qd[0], 1);                                            
                                                //
                                                if(!doNotUpdatePos)
                                                {
                                                        btScalar *pRealBuf = const_cast<btScalar *>(bod->getVelocityVector());
                                                        pRealBuf += 6 + bod->getNumDofs() + bod->getNumDofs()*bod->getNumDofs();
 
                                                        for(int i = 0; i < numDofs; ++i)
                                                                pRealBuf[i] = delta_q[i];
 
                                                        //bod->stepPositionsMultiDof(1, 0, &delta_q[0]);
                                                        bod->setPosUpdated(true);                                                       
                                                }
 
                                                //ugly hack which resets the cached data to t0 (needed for constraint solver)
                                                {
                                                        for(int link = 0; link < bod->getNumLinks(); ++link)
                                                                bod->getLink(link).updateCacheMultiDof();
                                                        bod->computeAccelerationsArticulatedBodyAlgorithmMultiDof(0, m_scratch_r, m_scratch_v, m_scratch_m);
                                                }
                                                
                                        }
                                }
                                
#ifndef BT_USE_VIRTUAL_CLEARFORCES_AND_GRAVITY
                                bod->clearForcesAndTorques();
#endif //BT_USE_VIRTUAL_CLEARFORCES_AND_GRAVITY
                        }//if (!isSleeping)
                }
        }
 
        clearMultiBodyConstraintForces();
 
        m_solverMultiBodyIslandCallback->processConstraints();
        
        m_constraintSolver->allSolved(solverInfo, m_debugDrawer);
 
        {
                BT_PROFILE("btMultiBody stepVelocities");
                for (int i=0;i<this->m_multiBodies.size();i++)
                {
                        btMultiBody* bod = m_multiBodies[i];
 
                        bool isSleeping = false;
 
                        if (bod->getBaseCollider() && bod->getBaseCollider()->getActivationState() == ISLAND_SLEEPING)
                        {
                                isSleeping = true;
                        }
                        for (int b=0;b<bod->getNumLinks();b++)
                        {
                                if (bod->getLink(b).m_collider && bod->getLink(b).m_collider->getActivationState()==ISLAND_SLEEPING)
                                        isSleeping = true;
                        }
 
                        if (!isSleeping)
                        {
                                //useless? they get resized in stepVelocities once again (AND DIFFERENTLY)
                                m_scratch_r.resize(bod->getNumLinks()+1);                 //multidof? ("Y"s use it and it is used to store qdd)
                                m_scratch_v.resize(bod->getNumLinks()+1);
                                m_scratch_m.resize(bod->getNumLinks()+1);
 
                                
                            {
                                if(!bod->isUsingRK4Integration())
                                {
                                                                        bool isConstraintPass = true;
                                    bod->computeAccelerationsArticulatedBodyAlgorithmMultiDof(solverInfo.m_timeStep, m_scratch_r, m_scratch_v, m_scratch_m, isConstraintPass);
                                }
                                }
                        }
                }
        }
 
        for (int i=0;i<this->m_multiBodies.size();i++)
        {
                btMultiBody* bod = m_multiBodies[i];
                bod->processDeltaVeeMultiDof2();
        }
 
}
 
void    btMultiBodyDynamicsWorld::integrateTransforms(btScalar timeStep)
{
        btDiscreteDynamicsWorld::integrateTransforms(timeStep);
 
        {
                BT_PROFILE("btMultiBody stepPositions");
                //integrate and update the Featherstone hierarchies
        
                for (int b=0;b<m_multiBodies.size();b++)
                {
                        btMultiBody* bod = m_multiBodies[b];
                        bool isSleeping = false;
                        if (bod->getBaseCollider() && bod->getBaseCollider()->getActivationState() == ISLAND_SLEEPING)
                        {
                                isSleeping = true;
                        } 
                        for (int b=0;b<bod->getNumLinks();b++)
                        {
                                if (bod->getLink(b).m_collider && bod->getLink(b).m_collider->getActivationState()==ISLAND_SLEEPING)
                                        isSleeping = true;
                        }
 
 
                        if (!isSleeping)
                        {
                                int nLinks = bod->getNumLinks();
 
                        
                                
                                {
                                        if(!bod->isPosUpdated())
                                                bod->stepPositionsMultiDof(timeStep);
                                        else
                                        {
                                                btScalar *pRealBuf = const_cast<btScalar *>(bod->getVelocityVector());
                                                pRealBuf += 6 + bod->getNumDofs() + bod->getNumDofs()*bod->getNumDofs();
 
                                                bod->stepPositionsMultiDof(1, 0, pRealBuf);
                                                bod->setPosUpdated(false);
                                        }
                                }
                                
                                m_scratch_world_to_local.resize(nLinks+1);
                                m_scratch_local_origin.resize(nLinks+1);
 
                                bod->updateCollisionObjectWorldTransforms(m_scratch_world_to_local,m_scratch_local_origin);
                                
                        } else
                        {
                                bod->clearVelocities();
                        }
                }
        }
}
 
 
 
void    btMultiBodyDynamicsWorld::addMultiBodyConstraint( btMultiBodyConstraint* constraint)
{
        m_multiBodyConstraints.push_back(constraint);
}
 
void    btMultiBodyDynamicsWorld::removeMultiBodyConstraint( btMultiBodyConstraint* constraint)
{
        m_multiBodyConstraints.remove(constraint);
}
 
void btMultiBodyDynamicsWorld::debugDrawMultiBodyConstraint(btMultiBodyConstraint* constraint)
{
        constraint->debugDraw(getDebugDrawer());
}
 
 
void    btMultiBodyDynamicsWorld::debugDrawWorld()
{
        BT_PROFILE("btMultiBodyDynamicsWorld debugDrawWorld");
 
        btDiscreteDynamicsWorld::debugDrawWorld();
 
        bool drawConstraints = false;
        if (getDebugDrawer())
        {
                int mode = getDebugDrawer()->getDebugMode();
                if (mode  & (btIDebugDraw::DBG_DrawConstraints | btIDebugDraw::DBG_DrawConstraintLimits))
                {
                        drawConstraints = true;
                }
 
                if (drawConstraints)
                {
                        BT_PROFILE("btMultiBody debugDrawWorld");
                        
 
                        for (int c=0;c<m_multiBodyConstraints.size();c++)
                        {
                                btMultiBodyConstraint* constraint = m_multiBodyConstraints[c];
                                debugDrawMultiBodyConstraint(constraint);
                        }
 
                        for (int b = 0; b<m_multiBodies.size(); b++)
                        {
                                btMultiBody* bod = m_multiBodies[b];
                                bod->forwardKinematics(m_scratch_world_to_local1,m_scratch_local_origin1);
                                
                                getDebugDrawer()->drawTransform(bod->getBaseWorldTransform(), 0.1);
 
 
                                for (int m = 0; m<bod->getNumLinks(); m++)
                                {
                                        
                                        const btTransform& tr = bod->getLink(m).m_cachedWorldTransform;
 
                                        getDebugDrawer()->drawTransform(tr, 0.1);
 
                                                //draw the joint axis
                                        if (bod->getLink(m).m_jointType==btMultibodyLink::eRevolute)
                                        {
                                                btVector3 vec = quatRotate(tr.getRotation(),bod->getLink(m).m_axes[0].m_topVec);
                                        
                                                btVector4 color(0,0,0,1);//1,1,1);
                                                btVector3 from = vec+tr.getOrigin()-quatRotate(tr.getRotation(),bod->getLink(m).m_dVector);
                                                btVector3 to = tr.getOrigin()-quatRotate(tr.getRotation(),bod->getLink(m).m_dVector);
                                                getDebugDrawer()->drawLine(from,to,color);
                                        }
                                        if (bod->getLink(m).m_jointType==btMultibodyLink::eFixed)
                                        {
                                                btVector3 vec = quatRotate(tr.getRotation(),bod->getLink(m).m_axes[0].m_bottomVec);
                                        
                                                btVector4 color(0,0,0,1);//1,1,1);
                                                btVector3 from = vec+tr.getOrigin()-quatRotate(tr.getRotation(),bod->getLink(m).m_dVector);
                                                btVector3 to = tr.getOrigin()-quatRotate(tr.getRotation(),bod->getLink(m).m_dVector);
                                                getDebugDrawer()->drawLine(from,to,color);
                                        }
                                        if (bod->getLink(m).m_jointType==btMultibodyLink::ePrismatic)
                                        {
                                                btVector3 vec = quatRotate(tr.getRotation(),bod->getLink(m).m_axes[0].m_bottomVec);
                                        
                                                btVector4 color(0,0,0,1);//1,1,1);
                                                btVector3 from = vec+tr.getOrigin()-quatRotate(tr.getRotation(),bod->getLink(m).m_dVector);
                                                btVector3 to = tr.getOrigin()-quatRotate(tr.getRotation(),bod->getLink(m).m_dVector);
                                                getDebugDrawer()->drawLine(from,to,color);
                                        }
                                        
                                }
                        }
                }
        }
 
        
}
 
 
 
void btMultiBodyDynamicsWorld::applyGravity()
{
        btDiscreteDynamicsWorld::applyGravity();
#ifdef BT_USE_VIRTUAL_CLEARFORCES_AND_GRAVITY
        BT_PROFILE("btMultiBody addGravity");
        for (int i=0;i<this->m_multiBodies.size();i++)
        {
                btMultiBody* bod = m_multiBodies[i];
 
                bool isSleeping = false;
 
                if (bod->getBaseCollider() && bod->getBaseCollider()->getActivationState() == ISLAND_SLEEPING)
                {
                        isSleeping = true;
                }
                for (int b=0;b<bod->getNumLinks();b++)
                {
                        if (bod->getLink(b).m_collider && bod->getLink(b).m_collider->getActivationState()==ISLAND_SLEEPING)
                                isSleeping = true;
                }
 
                if (!isSleeping)
                {
                        bod->addBaseForce(m_gravity * bod->getBaseMass());
 
                        for (int j = 0; j < bod->getNumLinks(); ++j)
                        {
                                bod->addLinkForce(j, m_gravity * bod->getLinkMass(j));
                        }
                }//if (!isSleeping)
        }
#endif //BT_USE_VIRTUAL_CLEARFORCES_AND_GRAVITY
}
 
void btMultiBodyDynamicsWorld::clearMultiBodyConstraintForces()
{ 
  for (int i=0;i<this->m_multiBodies.size();i++)
                {       
                        btMultiBody* bod = m_multiBodies[i];
                        bod->clearConstraintForces();
                  } 
}
void btMultiBodyDynamicsWorld::clearMultiBodyForces()
{
              {
               // BT_PROFILE("clearMultiBodyForces");
                for (int i=0;i<this->m_multiBodies.size();i++)
                {
                        btMultiBody* bod = m_multiBodies[i];
 
                        bool isSleeping = false;
 
                        if (bod->getBaseCollider() && bod->getBaseCollider()->getActivationState() == ISLAND_SLEEPING)
                        {       
                                isSleeping = true;
                        }
                        for (int b=0;b<bod->getNumLinks();b++)
                        {       
                                if (bod->getLink(b).m_collider && bod->getLink(b).m_collider->getActivationState()==ISLAND_SLEEPING)     
                                        isSleeping = true;
                        }
 
                        if (!isSleeping)
                        {
                        btMultiBody* bod = m_multiBodies[i];
                        bod->clearForcesAndTorques();
                        }
                }
        }
 
}
void btMultiBodyDynamicsWorld::clearForces()
{
        btDiscreteDynamicsWorld::clearForces();
 
#ifdef BT_USE_VIRTUAL_CLEARFORCES_AND_GRAVITY
        clearMultiBodyForces();
#endif
}
 
 
 
 
void    btMultiBodyDynamicsWorld::serialize(btSerializer* serializer)
{
 
        serializer->startSerialization();
 
        serializeDynamicsWorldInfo( serializer);
 
        serializeMultiBodies(serializer);
 
        serializeRigidBodies(serializer);
 
        serializeCollisionObjects(serializer);
 
        serializer->finishSerialization();
}
 
void    btMultiBodyDynamicsWorld::serializeMultiBodies(btSerializer* serializer)
{
        int i;
        //serialize all collision objects
        for (i=0;i<m_multiBodies.size();i++)
        {
                btMultiBody* mb = m_multiBodies[i];
                {
                        int len = mb->calculateSerializeBufferSize();
                        btChunk* chunk = serializer->allocate(len,1);
                        const char* structType = mb->serialize(chunk->m_oldPtr, serializer);
                        serializer->finalizeChunk(chunk,structType,BT_MULTIBODY_CODE,mb);
                }
        }
 
}