source: code/branches/physics/src/bullet/BulletDynamics/ConstraintSolver/btSequentialImpulseConstraintSolver.cpp @ 1963

/*
Bullet Continuous Collision Detection and Physics Library
Copyright (c) 2003-2006 Erwin Coumans  http://continuousphysics.com/Bullet/

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.
*/

//#define COMPUTE_IMPULSE_DENOM 1
//It is not necessary (redundant) to refresh contact manifolds, this refresh has been moved to the collision algorithms.
//#define FORCE_REFESH_CONTACT_MANIFOLDS 1

#include "btSequentialImpulseConstraintSolver.h"
#include "BulletCollision/NarrowPhaseCollision/btPersistentManifold.h"
#include "BulletDynamics/Dynamics/btRigidBody.h"
#include "btContactConstraint.h"
#include "btSolve2LinearConstraint.h"
#include "btContactSolverInfo.h"
#include "LinearMath/btIDebugDraw.h"
#include "btJacobianEntry.h"
#include "LinearMath/btMinMax.h"
#include "BulletDynamics/ConstraintSolver/btTypedConstraint.h"
#include <new>
#include "LinearMath/btStackAlloc.h"
#include "LinearMath/btQuickprof.h"
#include "btSolverBody.h"
#include "btSolverConstraint.h"


#include "LinearMath/btAlignedObjectArray.h"


int totalCpd = 0;

int     gTotalContactPoints = 0;

struct  btOrderIndex
{
        int     m_manifoldIndex;
        int     m_pointIndex;
};



#define SEQUENTIAL_IMPULSE_MAX_SOLVER_POINTS 16384
static btOrderIndex     gOrder[SEQUENTIAL_IMPULSE_MAX_SOLVER_POINTS];


unsigned long btSequentialImpulseConstraintSolver::btRand2()
{
  m_btSeed2 = (1664525L*m_btSeed2 + 1013904223L) & 0xffffffff;
  return m_btSeed2;
}



//See ODE: adam's all-int straightforward(?) dRandInt (0..n-1)
int btSequentialImpulseConstraintSolver::btRandInt2 (int n)
{
  // seems good; xor-fold and modulus
  const unsigned long un = static_cast<unsigned long>(n);
  unsigned long r = btRand2();

  // note: probably more aggressive than it needs to be -- might be
  //       able to get away without one or two of the innermost branches.
  if (un <= 0x00010000UL) {
    r ^= (r >> 16);
    if (un <= 0x00000100UL) {
      r ^= (r >> 8);
      if (un <= 0x00000010UL) {
        r ^= (r >> 4);
        if (un <= 0x00000004UL) {
          r ^= (r >> 2);
          if (un <= 0x00000002UL) {
            r ^= (r >> 1);
          }
        }
     }
    }
   }

  return (int) (r % un);
}




bool  MyContactDestroyedCallback(void* userPersistentData);
bool  MyContactDestroyedCallback(void* userPersistentData)
{
        assert (userPersistentData);
        btConstraintPersistentData* cpd = (btConstraintPersistentData*)userPersistentData;
        btAlignedFree(cpd);
        totalCpd--;
        //printf("totalCpd = %i. DELETED Ptr %x\n",totalCpd,userPersistentData);
        return true;
}



btSequentialImpulseConstraintSolver::btSequentialImpulseConstraintSolver()
:m_btSeed2(0)
{
        gContactDestroyedCallback = &MyContactDestroyedCallback;

        //initialize default friction/contact funcs
        int i,j;
        for (i=0;i<MAX_CONTACT_SOLVER_TYPES;i++)
                for (j=0;j<MAX_CONTACT_SOLVER_TYPES;j++)
                {

                        m_contactDispatch[i][j] = resolveSingleCollision;
                        m_frictionDispatch[i][j] = resolveSingleFriction;
                }
}

btSequentialImpulseConstraintSolver::~btSequentialImpulseConstraintSolver()
{

}

void    initSolverBody(btSolverBody* solverBody, btCollisionObject* collisionObject);
void    initSolverBody(btSolverBody* solverBody, btCollisionObject* collisionObject)
{
        btRigidBody* rb = btRigidBody::upcast(collisionObject);
        if (rb)
        {
                solverBody->m_angularVelocity = rb->getAngularVelocity() ;
                solverBody->m_centerOfMassPosition = collisionObject->getWorldTransform().getOrigin();
                solverBody->m_friction = collisionObject->getFriction();
                solverBody->m_invMass = rb->getInvMass();
                solverBody->m_linearVelocity = rb->getLinearVelocity();
                solverBody->m_originalBody = rb;
                solverBody->m_angularFactor = rb->getAngularFactor();
        } else
        {
                solverBody->m_angularVelocity.setValue(0,0,0);
                solverBody->m_centerOfMassPosition = collisionObject->getWorldTransform().getOrigin();
                solverBody->m_friction = collisionObject->getFriction();
                solverBody->m_invMass = 0.f;
                solverBody->m_linearVelocity.setValue(0,0,0);
                solverBody->m_originalBody = 0;
                solverBody->m_angularFactor = 1.f;
        }
        solverBody->m_pushVelocity.setValue(0.f,0.f,0.f);
        solverBody->m_turnVelocity.setValue(0.f,0.f,0.f);
}


int             gNumSplitImpulseRecoveries = 0;

btScalar restitutionCurve(btScalar rel_vel, btScalar restitution);
btScalar restitutionCurve(btScalar rel_vel, btScalar restitution)
{
        btScalar rest = restitution * -rel_vel;
        return rest;
}


void    resolveSplitPenetrationImpulseCacheFriendly(
        btSolverBody& body1,
        btSolverBody& body2,
        const btSolverConstraint& contactConstraint,
        const btContactSolverInfo& solverInfo);

//SIMD_FORCE_INLINE
void    resolveSplitPenetrationImpulseCacheFriendly(
        btSolverBody& body1,
        btSolverBody& body2,
        const btSolverConstraint& contactConstraint,
        const btContactSolverInfo& solverInfo)
{
        (void)solverInfo;

                if (contactConstraint.m_penetration < solverInfo.m_splitImpulsePenetrationThreshold)
        {

                                gNumSplitImpulseRecoveries++;
                btScalar normalImpulse;

                //  Optimized version of projected relative velocity, use precomputed cross products with normal
                //      body1.getVelocityInLocalPoint(contactConstraint.m_rel_posA,vel1);
                //      body2.getVelocityInLocalPoint(contactConstraint.m_rel_posB,vel2);
                //      btVector3 vel = vel1 - vel2;
                //      btScalar  rel_vel = contactConstraint.m_contactNormal.dot(vel);

                btScalar rel_vel;
                btScalar vel1Dotn = contactConstraint.m_contactNormal.dot(body1.m_pushVelocity)
                + contactConstraint.m_relpos1CrossNormal.dot(body1.m_turnVelocity);
                btScalar vel2Dotn = contactConstraint.m_contactNormal.dot(body2.m_pushVelocity)
                + contactConstraint.m_relpos2CrossNormal.dot(body2.m_turnVelocity);

                rel_vel = vel1Dotn-vel2Dotn;


                                btScalar positionalError = -contactConstraint.m_penetration * solverInfo.m_erp2/solverInfo.m_timeStep;
                //      btScalar positionalError = contactConstraint.m_penetration;

                btScalar velocityError = contactConstraint.m_restitution - rel_vel;// * damping;

                btScalar penetrationImpulse = positionalError * contactConstraint.m_jacDiagABInv;
                btScalar        velocityImpulse = velocityError * contactConstraint.m_jacDiagABInv;
                normalImpulse = penetrationImpulse+velocityImpulse;

                // See Erin Catto's GDC 2006 paper: Clamp the accumulated impulse
                btScalar oldNormalImpulse = contactConstraint.m_appliedPushImpulse;
                btScalar sum = oldNormalImpulse + normalImpulse;
                contactConstraint.m_appliedPushImpulse = btScalar(0.) > sum ? btScalar(0.): sum;

                normalImpulse = contactConstraint.m_appliedPushImpulse - oldNormalImpulse;

                                body1.internalApplyPushImpulse(contactConstraint.m_contactNormal*body1.m_invMass, contactConstraint.m_angularComponentA,normalImpulse);
               
                                body2.internalApplyPushImpulse(contactConstraint.m_contactNormal*body2.m_invMass, contactConstraint.m_angularComponentB,-normalImpulse);
               
        }

}


//velocity + friction
//response  between two dynamic objects with friction

btScalar resolveSingleCollisionCombinedCacheFriendly(
        btSolverBody& body1,
        btSolverBody& body2,
        const btSolverConstraint& contactConstraint,
        const btContactSolverInfo& solverInfo);

//SIMD_FORCE_INLINE 
btScalar resolveSingleCollisionCombinedCacheFriendly(
        btSolverBody& body1,
        btSolverBody& body2,
        const btSolverConstraint& contactConstraint,
        const btContactSolverInfo& solverInfo)
{
        (void)solverInfo;

        btScalar normalImpulse;

        {

                
                //  Optimized version of projected relative velocity, use precomputed cross products with normal
                //      body1.getVelocityInLocalPoint(contactConstraint.m_rel_posA,vel1);
                //      body2.getVelocityInLocalPoint(contactConstraint.m_rel_posB,vel2);
                //      btVector3 vel = vel1 - vel2;
                //      btScalar  rel_vel = contactConstraint.m_contactNormal.dot(vel);

                btScalar rel_vel;
                btScalar vel1Dotn = contactConstraint.m_contactNormal.dot(body1.m_linearVelocity) 
                                        + contactConstraint.m_relpos1CrossNormal.dot(body1.m_angularVelocity);
                btScalar vel2Dotn = contactConstraint.m_contactNormal.dot(body2.m_linearVelocity) 
                                        + contactConstraint.m_relpos2CrossNormal.dot(body2.m_angularVelocity);

                rel_vel = vel1Dotn-vel2Dotn;

                btScalar positionalError = 0.f;
                if (!solverInfo.m_splitImpulse || (contactConstraint.m_penetration > solverInfo.m_splitImpulsePenetrationThreshold))
                {
                        positionalError = -contactConstraint.m_penetration * solverInfo.m_erp/solverInfo.m_timeStep;
                }

                btScalar velocityError = contactConstraint.m_restitution - rel_vel;// * damping;

                btScalar penetrationImpulse = positionalError * contactConstraint.m_jacDiagABInv;
                btScalar        velocityImpulse = velocityError * contactConstraint.m_jacDiagABInv;
                normalImpulse = penetrationImpulse+velocityImpulse;
                
                
                // See Erin Catto's GDC 2006 paper: Clamp the accumulated impulse
                btScalar oldNormalImpulse = contactConstraint.m_appliedImpulse;
                btScalar sum = oldNormalImpulse + normalImpulse;
                contactConstraint.m_appliedImpulse = btScalar(0.) > sum ? btScalar(0.): sum;

                normalImpulse = contactConstraint.m_appliedImpulse - oldNormalImpulse;

                body1.internalApplyImpulse(contactConstraint.m_contactNormal*body1.m_invMass,
                                contactConstraint.m_angularComponentA,normalImpulse);
                
                body2.internalApplyImpulse(contactConstraint.m_contactNormal*body2.m_invMass,
                                contactConstraint.m_angularComponentB,-normalImpulse);
        }

        return normalImpulse;
}


#ifndef NO_FRICTION_TANGENTIALS

btScalar resolveSingleFrictionCacheFriendly(
        btSolverBody& body1,
        btSolverBody& body2,
        const btSolverConstraint& contactConstraint,
        const btContactSolverInfo& solverInfo,
        btScalar appliedNormalImpulse);

//SIMD_FORCE_INLINE 
btScalar resolveSingleFrictionCacheFriendly(
        btSolverBody& body1,
        btSolverBody& body2,
        const btSolverConstraint& contactConstraint,
        const btContactSolverInfo& solverInfo,
        btScalar appliedNormalImpulse)
{
        (void)solverInfo;

        
        const btScalar combinedFriction = contactConstraint.m_friction;
        
        const btScalar limit = appliedNormalImpulse * combinedFriction;
        
        if (appliedNormalImpulse>btScalar(0.))
        //friction
        {
                
                btScalar j1;
                {

                        btScalar rel_vel;
                        const btScalar vel1Dotn = contactConstraint.m_contactNormal.dot(body1.m_linearVelocity) 
                                                + contactConstraint.m_relpos1CrossNormal.dot(body1.m_angularVelocity);
                        const btScalar vel2Dotn = contactConstraint.m_contactNormal.dot(body2.m_linearVelocity) 
                                + contactConstraint.m_relpos2CrossNormal.dot(body2.m_angularVelocity);
                        rel_vel = vel1Dotn-vel2Dotn;

                        // calculate j that moves us to zero relative velocity
                        j1 = -rel_vel * contactConstraint.m_jacDiagABInv;
#define CLAMP_ACCUMULATED_FRICTION_IMPULSE 1
#ifdef CLAMP_ACCUMULATED_FRICTION_IMPULSE
                        btScalar oldTangentImpulse = contactConstraint.m_appliedImpulse;
                        contactConstraint.m_appliedImpulse = oldTangentImpulse + j1;
                        
                        if (limit < contactConstraint.m_appliedImpulse)
                        {
                                contactConstraint.m_appliedImpulse = limit;
                        } else
                        {
                                if (contactConstraint.m_appliedImpulse < -limit)
                                        contactConstraint.m_appliedImpulse = -limit;
                        }
                        j1 = contactConstraint.m_appliedImpulse - oldTangentImpulse;
#else
                        if (limit < j1)
                        {
                                j1 = limit;
                        } else
                        {
                                if (j1 < -limit)
                                        j1 = -limit;
                        }

#endif //CLAMP_ACCUMULATED_FRICTION_IMPULSE

                        //GEN_set_min(contactConstraint.m_appliedImpulse, limit);
                        //GEN_set_max(contactConstraint.m_appliedImpulse, -limit);

                        

                }
        
                body1.internalApplyImpulse(contactConstraint.m_contactNormal*body1.m_invMass,contactConstraint.m_angularComponentA,j1);
                
                body2.internalApplyImpulse(contactConstraint.m_contactNormal*body2.m_invMass,contactConstraint.m_angularComponentB,-j1);

        } 
        return 0.f;
}


#else

//velocity + friction
//response  between two dynamic objects with friction
btScalar resolveSingleFrictionCacheFriendly(
        btSolverBody& body1,
        btSolverBody& body2,
        btSolverConstraint& contactConstraint,
        const btContactSolverInfo& solverInfo)
{

        btVector3 vel1;
        btVector3 vel2;
        btScalar normalImpulse(0.f);

        {
                const btVector3& normal = contactConstraint.m_contactNormal;
                if (contactConstraint.m_penetration < 0.f)
                        return 0.f;


                body1.getVelocityInLocalPoint(contactConstraint.m_rel_posA,vel1);
                body2.getVelocityInLocalPoint(contactConstraint.m_rel_posB,vel2);
                btVector3 vel = vel1 - vel2;
                btScalar rel_vel;
                rel_vel = normal.dot(vel);

                btVector3 lat_vel = vel - normal * rel_vel;
                btScalar lat_rel_vel = lat_vel.length2();

                btScalar combinedFriction = contactConstraint.m_friction;
                const btVector3& rel_pos1 = contactConstraint.m_rel_posA;
                const btVector3& rel_pos2 = contactConstraint.m_rel_posB;


                if (lat_rel_vel > SIMD_EPSILON*SIMD_EPSILON)
                {
                        lat_rel_vel = btSqrt(lat_rel_vel);

                        lat_vel /= lat_rel_vel;
                        btVector3 temp1 = body1.m_invInertiaWorld * rel_pos1.cross(lat_vel);
                        btVector3 temp2 = body2.m_invInertiaWorld * rel_pos2.cross(lat_vel);
                        btScalar friction_impulse = lat_rel_vel /
                                (body1.m_invMass + body2.m_invMass + lat_vel.dot(temp1.cross(rel_pos1) + temp2.cross(rel_pos2)));
                        btScalar normal_impulse = contactConstraint.m_appliedImpulse * combinedFriction;

                        GEN_set_min(friction_impulse, normal_impulse);
                        GEN_set_max(friction_impulse, -normal_impulse);
                        body1.applyImpulse(lat_vel * -friction_impulse, rel_pos1);
                        body2.applyImpulse(lat_vel * friction_impulse, rel_pos2);
                }
        }

        return normalImpulse;
}

#endif //NO_FRICTION_TANGENTIALS





void    btSequentialImpulseConstraintSolver::addFrictionConstraint(const btVector3& normalAxis,int solverBodyIdA,int solverBodyIdB,int frictionIndex,btManifoldPoint& cp,const btVector3& rel_pos1,const btVector3& rel_pos2,btCollisionObject* colObj0,btCollisionObject* colObj1, btScalar relaxation)
{

        btRigidBody* body0=btRigidBody::upcast(colObj0);
        btRigidBody* body1=btRigidBody::upcast(colObj1);

        btSolverConstraint& solverConstraint = m_tmpSolverFrictionConstraintPool.expand();
        solverConstraint.m_contactNormal = normalAxis;

        solverConstraint.m_solverBodyIdA = solverBodyIdA;
        solverConstraint.m_solverBodyIdB = solverBodyIdB;
        solverConstraint.m_constraintType = btSolverConstraint::BT_SOLVER_FRICTION_1D;
        solverConstraint.m_frictionIndex = frictionIndex;

        solverConstraint.m_friction = cp.m_combinedFriction;
        solverConstraint.m_originalContactPoint = 0;

        solverConstraint.m_appliedImpulse = btScalar(0.);
        solverConstraint.m_appliedPushImpulse = 0.f;
        solverConstraint.m_penetration = 0.f;
        {
                btVector3 ftorqueAxis1 = rel_pos1.cross(solverConstraint.m_contactNormal);
                solverConstraint.m_relpos1CrossNormal = ftorqueAxis1;
                solverConstraint.m_angularComponentA = body0 ? body0->getInvInertiaTensorWorld()*ftorqueAxis1 : btVector3(0,0,0);
        }
        {
                btVector3 ftorqueAxis1 = rel_pos2.cross(solverConstraint.m_contactNormal);
                solverConstraint.m_relpos2CrossNormal = ftorqueAxis1;
                solverConstraint.m_angularComponentB = body1 ? body1->getInvInertiaTensorWorld()*ftorqueAxis1 : btVector3(0,0,0);
        }

#ifdef COMPUTE_IMPULSE_DENOM
        btScalar denom0 = rb0->computeImpulseDenominator(pos1,solverConstraint.m_contactNormal);
        btScalar denom1 = rb1->computeImpulseDenominator(pos2,solverConstraint.m_contactNormal);
#else
        btVector3 vec;
        btScalar denom0 = 0.f;
        btScalar denom1 = 0.f;
        if (body0)
        {
                vec = ( solverConstraint.m_angularComponentA).cross(rel_pos1);
                denom0 = body0->getInvMass() + normalAxis.dot(vec);
        }
        if (body1)
        {
                vec = ( solverConstraint.m_angularComponentB).cross(rel_pos2);
                denom1 = body1->getInvMass() + normalAxis.dot(vec);
        }


#endif //COMPUTE_IMPULSE_DENOM
        btScalar denom = relaxation/(denom0+denom1);
        solverConstraint.m_jacDiagABInv = denom;


}



btScalar btSequentialImpulseConstraintSolver::solveGroupCacheFriendlySetup(btCollisionObject** /*bodies */,int /*numBodies */,btPersistentManifold** manifoldPtr, int numManifolds,btTypedConstraint** constraints,int numConstraints,const btContactSolverInfo& infoGlobal,btIDebugDraw* debugDrawer,btStackAlloc* stackAlloc)
{
        BT_PROFILE("solveGroupCacheFriendlySetup");
        (void)stackAlloc;
        (void)debugDrawer;


        if (!(numConstraints + numManifolds))
        {
//              printf("empty\n");
                return 0.f;
        }
        btPersistentManifold* manifold = 0;
        btCollisionObject* colObj0=0,*colObj1=0;

        //btRigidBody* rb0=0,*rb1=0;


#ifdef FORCE_REFESH_CONTACT_MANIFOLDS

        BEGIN_PROFILE("refreshManifolds");

        int i;
        
        

        for (i=0;i<numManifolds;i++)
        {
                manifold = manifoldPtr[i];
                rb1 = (btRigidBody*)manifold->getBody1();
                rb0 = (btRigidBody*)manifold->getBody0();
                
                manifold->refreshContactPoints(rb0->getCenterOfMassTransform(),rb1->getCenterOfMassTransform());

        }

        END_PROFILE("refreshManifolds");
#endif //FORCE_REFESH_CONTACT_MANIFOLDS

        



        //int sizeofSB = sizeof(btSolverBody);
        //int sizeofSC = sizeof(btSolverConstraint);


        //if (1)
        {
                //if m_stackAlloc, try to pack bodies/constraints to speed up solving
//              btBlock*                                        sablock;
//              sablock = stackAlloc->beginBlock();

        //      int memsize = 16;
//              unsigned char* stackMemory = stackAlloc->allocate(memsize);

                
                //todo: use stack allocator for this temp memory
//              int minReservation = numManifolds*2;

                //m_tmpSolverBodyPool.reserve(minReservation);

                //don't convert all bodies, only the one we need so solver the constraints
/*
                {
                        for (int i=0;i<numBodies;i++)
                        {
                                btRigidBody* rb = btRigidBody::upcast(bodies[i]);
                                if (rb &&       (rb->getIslandTag() >= 0))
                                {
                                        btAssert(rb->getCompanionId() < 0);
                                        int solverBodyId = m_tmpSolverBodyPool.size();
                                        btSolverBody& solverBody = m_tmpSolverBodyPool.expand();
                                        initSolverBody(&solverBody,rb);
                                        rb->setCompanionId(solverBodyId);
                                } 
                        }
                }
*/
                
                //m_tmpSolverConstraintPool.reserve(minReservation);
                //m_tmpSolverFrictionConstraintPool.reserve(minReservation);

                {
                        int i;

                        for (i=0;i<numManifolds;i++)
                        {
                                manifold = manifoldPtr[i];
                                colObj0 = (btCollisionObject*)manifold->getBody0();
                                colObj1 = (btCollisionObject*)manifold->getBody1();
                        
                                int solverBodyIdA=-1;
                                int solverBodyIdB=-1;

                                if (manifold->getNumContacts())
                                {

                                        

                                        if (colObj0->getIslandTag() >= 0)
                                        {
                                                if (colObj0->getCompanionId() >= 0)
                                                {
                                                        //body has already been converted
                                                        solverBodyIdA = colObj0->getCompanionId();
                                                } else
                                                {
                                                        solverBodyIdA = m_tmpSolverBodyPool.size();
                                                        btSolverBody& solverBody = m_tmpSolverBodyPool.expand();
                                                        initSolverBody(&solverBody,colObj0);
                                                        colObj0->setCompanionId(solverBodyIdA);
                                                }
                                        } else
                                        {
                                                //create a static body
                                                solverBodyIdA = m_tmpSolverBodyPool.size();
                                                btSolverBody& solverBody = m_tmpSolverBodyPool.expand();
                                                initSolverBody(&solverBody,colObj0);
                                        }

                                        if (colObj1->getIslandTag() >= 0)
                                        {
                                                if (colObj1->getCompanionId() >= 0)
                                                {
                                                        solverBodyIdB = colObj1->getCompanionId();
                                                } else
                                                {
                                                        solverBodyIdB = m_tmpSolverBodyPool.size();
                                                        btSolverBody& solverBody = m_tmpSolverBodyPool.expand();
                                                        initSolverBody(&solverBody,colObj1);
                                                        colObj1->setCompanionId(solverBodyIdB);
                                                }
                                        } else
                                        {
                                                //create a static body
                                                solverBodyIdB = m_tmpSolverBodyPool.size();
                                                btSolverBody& solverBody = m_tmpSolverBodyPool.expand();
                                                initSolverBody(&solverBody,colObj1);
                                        }
                                }

                                btVector3 rel_pos1;
                                btVector3 rel_pos2;
                                btScalar relaxation;

                                for (int j=0;j<manifold->getNumContacts();j++)
                                {
                                        
                                        btManifoldPoint& cp = manifold->getContactPoint(j);
                                        
                                        if (cp.getDistance() <= btScalar(0.))
                                        {
                                                
                                                const btVector3& pos1 = cp.getPositionWorldOnA();
                                                const btVector3& pos2 = cp.getPositionWorldOnB();

                                                 rel_pos1 = pos1 - colObj0->getWorldTransform().getOrigin(); 
                                                 rel_pos2 = pos2 - colObj1->getWorldTransform().getOrigin();

                                                
                                                relaxation = 1.f;
                                                btScalar rel_vel;
                                                btVector3 vel;

                                                int frictionIndex = m_tmpSolverConstraintPool.size();

                                                {
                                                        btSolverConstraint& solverConstraint = m_tmpSolverConstraintPool.expand();
                                                        btRigidBody* rb0 = btRigidBody::upcast(colObj0);
                                                        btRigidBody* rb1 = btRigidBody::upcast(colObj1);

                                                        solverConstraint.m_solverBodyIdA = solverBodyIdA;
                                                        solverConstraint.m_solverBodyIdB = solverBodyIdB;
                                                        solverConstraint.m_constraintType = btSolverConstraint::BT_SOLVER_CONTACT_1D;

                                                        solverConstraint.m_originalContactPoint = &cp;

                                                        btVector3 torqueAxis0 = rel_pos1.cross(cp.m_normalWorldOnB);
                                                        solverConstraint.m_angularComponentA = rb0 ? rb0->getInvInertiaTensorWorld()*torqueAxis0 : btVector3(0,0,0);
                                                        btVector3 torqueAxis1 = rel_pos2.cross(cp.m_normalWorldOnB);            
                                                        solverConstraint.m_angularComponentB = rb1 ? rb1->getInvInertiaTensorWorld()*torqueAxis1 : btVector3(0,0,0);
                                                        {
#ifdef COMPUTE_IMPULSE_DENOM
                                                                btScalar denom0 = rb0->computeImpulseDenominator(pos1,cp.m_normalWorldOnB);
                                                                btScalar denom1 = rb1->computeImpulseDenominator(pos2,cp.m_normalWorldOnB);
#else                                                   
                                                                btVector3 vec;
                                                                btScalar denom0 = 0.f;
                                                                btScalar denom1 = 0.f;
                                                                if (rb0)
                                                                {
                                                                        vec = ( solverConstraint.m_angularComponentA).cross(rel_pos1);
                                                                        denom0 = rb0->getInvMass() + cp.m_normalWorldOnB.dot(vec);
                                                                }
                                                                if (rb1)
                                                                {
                                                                        vec = ( solverConstraint.m_angularComponentB).cross(rel_pos2);
                                                                        denom1 = rb1->getInvMass() + cp.m_normalWorldOnB.dot(vec);
                                                                }
#endif //COMPUTE_IMPULSE_DENOM          
                                                                
                                                                btScalar denom = relaxation/(denom0+denom1);
                                                                solverConstraint.m_jacDiagABInv = denom;
                                                        }

                                                        solverConstraint.m_contactNormal = cp.m_normalWorldOnB;
                                                        solverConstraint.m_relpos1CrossNormal = rel_pos1.cross(cp.m_normalWorldOnB);
                                                        solverConstraint.m_relpos2CrossNormal = rel_pos2.cross(cp.m_normalWorldOnB);


                                                        btVector3 vel1 = rb0 ? rb0->getVelocityInLocalPoint(rel_pos1) : btVector3(0,0,0);
                                                        btVector3 vel2 = rb1 ? rb1->getVelocityInLocalPoint(rel_pos2) : btVector3(0,0,0);
                                
                                                        vel  = vel1 - vel2;
                                                        
                                                        rel_vel = cp.m_normalWorldOnB.dot(vel);
                                                        
                                                        solverConstraint.m_penetration = btMin(cp.getDistance()+infoGlobal.m_linearSlop,btScalar(0.));
                                                        //solverConstraint.m_penetration = cp.getDistance();

                                                        solverConstraint.m_friction = cp.m_combinedFriction;

                                                        
                                                        if (cp.m_lifeTime>infoGlobal.m_restingContactRestitutionThreshold)
                                                        {
                                                                solverConstraint.m_restitution = 0.f;
                                                        } else
                                                        {
                                                                solverConstraint.m_restitution =  restitutionCurve(rel_vel, cp.m_combinedRestitution);
                                                                if (solverConstraint.m_restitution <= btScalar(0.))
                                                                {
                                                                        solverConstraint.m_restitution = 0.f;
                                                                };
                                                        }

                                                        
                                                        btScalar penVel = -solverConstraint.m_penetration/infoGlobal.m_timeStep;

                                                        

                                                        if (solverConstraint.m_restitution > penVel)
                                                        {
                                                                solverConstraint.m_penetration = btScalar(0.);
                                                        }
                                                         
                                                        
                                                        
                                                        ///warm starting (or zero if disabled)
                                                        if (infoGlobal.m_solverMode & SOLVER_USE_WARMSTARTING)
                                                        {
                                                                solverConstraint.m_appliedImpulse = cp.m_appliedImpulse * infoGlobal.m_warmstartingFactor;
                                                                if (rb0)
                                                                        m_tmpSolverBodyPool[solverConstraint.m_solverBodyIdA].internalApplyImpulse(solverConstraint.m_contactNormal*rb0->getInvMass(),solverConstraint.m_angularComponentA,solverConstraint.m_appliedImpulse);
                                                                if (rb1)
                                                                        m_tmpSolverBodyPool[solverConstraint.m_solverBodyIdB].internalApplyImpulse(solverConstraint.m_contactNormal*rb1->getInvMass(),solverConstraint.m_angularComponentB,-solverConstraint.m_appliedImpulse);
                                                        } else
                                                        {
                                                                solverConstraint.m_appliedImpulse = 0.f;
                                                        }

                                                        solverConstraint.m_appliedPushImpulse = 0.f;
                                                        
                                                        solverConstraint.m_frictionIndex = m_tmpSolverFrictionConstraintPool.size();
                                                        if (!cp.m_lateralFrictionInitialized)
                                                        {
                                                                cp.m_lateralFrictionDir1 = vel - cp.m_normalWorldOnB * rel_vel;
                                                                btScalar lat_rel_vel = cp.m_lateralFrictionDir1.length2();
                                                                if (lat_rel_vel > SIMD_EPSILON)//0.0f)
                                                                {
                                                                        cp.m_lateralFrictionDir1 /= btSqrt(lat_rel_vel);
                                                                        addFrictionConstraint(cp.m_lateralFrictionDir1,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
                                                                        cp.m_lateralFrictionDir2 = cp.m_lateralFrictionDir1.cross(cp.m_normalWorldOnB);
                                                                        cp.m_lateralFrictionDir2.normalize();//??
                                                                        addFrictionConstraint(cp.m_lateralFrictionDir2,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
                                                                } else
                                                                {
                                                                        //re-calculate friction direction every frame, todo: check if this is really needed
                                                                        
                                                                        btPlaneSpace1(cp.m_normalWorldOnB,cp.m_lateralFrictionDir1,cp.m_lateralFrictionDir2);
                                                                        addFrictionConstraint(cp.m_lateralFrictionDir1,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
                                                                        addFrictionConstraint(cp.m_lateralFrictionDir2,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
                                                                }
                                                                cp.m_lateralFrictionInitialized = true;
                                                                
                                                        } else
                                                        {
                                                                addFrictionConstraint(cp.m_lateralFrictionDir1,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
                                                                addFrictionConstraint(cp.m_lateralFrictionDir2,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
                                                        }

                                                        {
                                                                btSolverConstraint& frictionConstraint1 = m_tmpSolverFrictionConstraintPool[solverConstraint.m_frictionIndex];
                                                                if (infoGlobal.m_solverMode & SOLVER_USE_WARMSTARTING)
                                                                {
                                                                        frictionConstraint1.m_appliedImpulse = cp.m_appliedImpulseLateral1 * infoGlobal.m_warmstartingFactor;
                                                                        if (rb0)
                                                                                m_tmpSolverBodyPool[solverConstraint.m_solverBodyIdA].internalApplyImpulse(frictionConstraint1.m_contactNormal*rb0->getInvMass(),frictionConstraint1.m_angularComponentA,frictionConstraint1.m_appliedImpulse);
                                                                        if (rb1)
                                                                                m_tmpSolverBodyPool[solverConstraint.m_solverBodyIdB].internalApplyImpulse(frictionConstraint1.m_contactNormal*rb1->getInvMass(),frictionConstraint1.m_angularComponentB,-frictionConstraint1.m_appliedImpulse);
                                                                } else
                                                                {
                                                                        frictionConstraint1.m_appliedImpulse = 0.f;
                                                                }
                                                        }
                                                        {
                                                                btSolverConstraint& frictionConstraint2 = m_tmpSolverFrictionConstraintPool[solverConstraint.m_frictionIndex+1];
                                                                if (infoGlobal.m_solverMode & SOLVER_USE_WARMSTARTING)
                                                                {
                                                                        frictionConstraint2.m_appliedImpulse = cp.m_appliedImpulseLateral2 * infoGlobal.m_warmstartingFactor;
                                                                        if (rb0)
                                                                                m_tmpSolverBodyPool[solverConstraint.m_solverBodyIdA].internalApplyImpulse(frictionConstraint2.m_contactNormal*rb0->getInvMass(),frictionConstraint2.m_angularComponentA,frictionConstraint2.m_appliedImpulse);
                                                                        if (rb1)
                                                                                m_tmpSolverBodyPool[solverConstraint.m_solverBodyIdB].internalApplyImpulse(frictionConstraint2.m_contactNormal*rb1->getInvMass(),frictionConstraint2.m_angularComponentB,-frictionConstraint2.m_appliedImpulse);
                                                                } else
                                                                {
                                                                        frictionConstraint2.m_appliedImpulse = 0.f;
                                                                }
                                                        }
                                                }


                                        }
                                }
                        }
                }
        }
        
        btContactSolverInfo info = infoGlobal;

        {
                int j;
                for (j=0;j<numConstraints;j++)
                {
                        btTypedConstraint* constraint = constraints[j];
                        constraint->buildJacobian();
                }
        }
        
        

        int numConstraintPool = m_tmpSolverConstraintPool.size();
        int numFrictionPool = m_tmpSolverFrictionConstraintPool.size();

        ///todo: use stack allocator for such temporarily memory, same for solver bodies/constraints
        m_orderTmpConstraintPool.resize(numConstraintPool);
        m_orderFrictionConstraintPool.resize(numFrictionPool);
        {
                int i;
                for (i=0;i<numConstraintPool;i++)
                {
                        m_orderTmpConstraintPool[i] = i;
                }
                for (i=0;i<numFrictionPool;i++)
                {
                        m_orderFrictionConstraintPool[i] = i;
                }
        }



        return 0.f;

}

btScalar btSequentialImpulseConstraintSolver::solveGroupCacheFriendlyIterations(btCollisionObject** /*bodies */,int /*numBodies*/,btPersistentManifold** /*manifoldPtr*/, int /*numManifolds*/,btTypedConstraint** constraints,int numConstraints,const btContactSolverInfo& infoGlobal,btIDebugDraw* /*debugDrawer*/,btStackAlloc* /*stackAlloc*/)
{
        BT_PROFILE("solveGroupCacheFriendlyIterations");
        int numConstraintPool = m_tmpSolverConstraintPool.size();
        int numFrictionPool = m_tmpSolverFrictionConstraintPool.size();

        //should traverse the contacts random order...
        int iteration;
        {
                for ( iteration = 0;iteration<infoGlobal.m_numIterations;iteration++)
                {                       

                        int j;
                        if (infoGlobal.m_solverMode & SOLVER_RANDMIZE_ORDER)
                        {
                                if ((iteration & 7) == 0) {
                                        for (j=0; j<numConstraintPool; ++j) {
                                                int tmp = m_orderTmpConstraintPool[j];
                                                int swapi = btRandInt2(j+1);
                                                m_orderTmpConstraintPool[j] = m_orderTmpConstraintPool[swapi];
                                                m_orderTmpConstraintPool[swapi] = tmp;
                                        }

                                        for (j=0; j<numFrictionPool; ++j) {
                                                int tmp = m_orderFrictionConstraintPool[j];
                                                int swapi = btRandInt2(j+1);
                                                m_orderFrictionConstraintPool[j] = m_orderFrictionConstraintPool[swapi];
                                                m_orderFrictionConstraintPool[swapi] = tmp;
                                        }
                                }
                        }

                        for (j=0;j<numConstraints;j++)
                        {
                                btTypedConstraint* constraint = constraints[j];
                                ///todo: use solver bodies, so we don't need to copy from/to btRigidBody

                                if ((constraint->getRigidBodyA().getIslandTag() >= 0) && (constraint->getRigidBodyA().getCompanionId() >= 0))
                                {
                                        m_tmpSolverBodyPool[constraint->getRigidBodyA().getCompanionId()].writebackVelocity();
                                }
                                if ((constraint->getRigidBodyB().getIslandTag() >= 0) && (constraint->getRigidBodyB().getCompanionId() >= 0))
                                {
                                        m_tmpSolverBodyPool[constraint->getRigidBodyB().getCompanionId()].writebackVelocity();
                                }

                                constraint->solveConstraint(infoGlobal.m_timeStep);

                                if ((constraint->getRigidBodyA().getIslandTag() >= 0) && (constraint->getRigidBodyA().getCompanionId() >= 0))
                                {
                                        m_tmpSolverBodyPool[constraint->getRigidBodyA().getCompanionId()].readVelocity();
                                }
                                if ((constraint->getRigidBodyB().getIslandTag() >= 0) && (constraint->getRigidBodyB().getCompanionId() >= 0))
                                {
                                        m_tmpSolverBodyPool[constraint->getRigidBodyB().getCompanionId()].readVelocity();
                                }

                        }

                        {
                                int numPoolConstraints = m_tmpSolverConstraintPool.size();
                                for (j=0;j<numPoolConstraints;j++)
                                {
                                        
                                        const btSolverConstraint& solveManifold = m_tmpSolverConstraintPool[m_orderTmpConstraintPool[j]];
                                        resolveSingleCollisionCombinedCacheFriendly(m_tmpSolverBodyPool[solveManifold.m_solverBodyIdA],
                                                m_tmpSolverBodyPool[solveManifold.m_solverBodyIdB],solveManifold,infoGlobal);
                                }
                        }

                        {
                                 int numFrictionPoolConstraints = m_tmpSolverFrictionConstraintPool.size();
                                
                                 for (j=0;j<numFrictionPoolConstraints;j++)
                                {
                                        const btSolverConstraint& solveManifold = m_tmpSolverFrictionConstraintPool[m_orderFrictionConstraintPool[j]];
                                        btScalar totalImpulse = m_tmpSolverConstraintPool[solveManifold.m_frictionIndex].m_appliedImpulse+
                                                                m_tmpSolverConstraintPool[solveManifold.m_frictionIndex].m_appliedPushImpulse;                  

                                                resolveSingleFrictionCacheFriendly(m_tmpSolverBodyPool[solveManifold.m_solverBodyIdA],
                                                        m_tmpSolverBodyPool[solveManifold.m_solverBodyIdB],solveManifold,infoGlobal,
                                                        totalImpulse);
                                }
                        }
                        


                }
        
                if (infoGlobal.m_splitImpulse)
                {
                        
                        for ( iteration = 0;iteration<infoGlobal.m_numIterations;iteration++)
                        {
                                {
                                        int numPoolConstraints = m_tmpSolverConstraintPool.size();
                                        int j;
                                        for (j=0;j<numPoolConstraints;j++)
                                        {
                                                const btSolverConstraint& solveManifold = m_tmpSolverConstraintPool[m_orderTmpConstraintPool[j]];

                                                resolveSplitPenetrationImpulseCacheFriendly(m_tmpSolverBodyPool[solveManifold.m_solverBodyIdA],
                                                        m_tmpSolverBodyPool[solveManifold.m_solverBodyIdB],solveManifold,infoGlobal);
                                        }
                                }
                        }

                }

        }

        return 0.f;
}


btScalar btSequentialImpulseConstraintSolver::solveGroupCacheFriendly(btCollisionObject** bodies,int numBodies,btPersistentManifold** manifoldPtr, int numManifolds,btTypedConstraint** constraints,int numConstraints,const btContactSolverInfo& infoGlobal,btIDebugDraw* debugDrawer,btStackAlloc* stackAlloc)
{
        int i;

        solveGroupCacheFriendlySetup( bodies, numBodies, manifoldPtr,  numManifolds,constraints, numConstraints,infoGlobal,debugDrawer, stackAlloc);
        solveGroupCacheFriendlyIterations(bodies, numBodies, manifoldPtr,  numManifolds,constraints, numConstraints,infoGlobal,debugDrawer, stackAlloc);

        int numPoolConstraints = m_tmpSolverConstraintPool.size();
        int j;
        for (j=0;j<numPoolConstraints;j++)
        {
                
                const btSolverConstraint& solveManifold = m_tmpSolverConstraintPool[j];
                btManifoldPoint* pt = (btManifoldPoint*) solveManifold.m_originalContactPoint;
                btAssert(pt);
                pt->m_appliedImpulse = solveManifold.m_appliedImpulse;
                pt->m_appliedImpulseLateral1 = m_tmpSolverFrictionConstraintPool[solveManifold.m_frictionIndex].m_appliedImpulse;
                pt->m_appliedImpulseLateral2 = m_tmpSolverFrictionConstraintPool[solveManifold.m_frictionIndex+1].m_appliedImpulse;

                //do a callback here?

        }

        if (infoGlobal.m_splitImpulse)
        {               
                for ( i=0;i<m_tmpSolverBodyPool.size();i++)
                {
                        m_tmpSolverBodyPool[i].writebackVelocity(infoGlobal.m_timeStep);
                }
        } else
        {
                for ( i=0;i<m_tmpSolverBodyPool.size();i++)
        {
                m_tmpSolverBodyPool[i].writebackVelocity();
        }
        }

//      printf("m_tmpSolverConstraintPool.size() = %i\n",m_tmpSolverConstraintPool.size());

/*
        printf("m_tmpSolverBodyPool.size() = %i\n",m_tmpSolverBodyPool.size());
        printf("m_tmpSolverConstraintPool.size() = %i\n",m_tmpSolverConstraintPool.size());
        printf("m_tmpSolverFrictionConstraintPool.size() = %i\n",m_tmpSolverFrictionConstraintPool.size());

        
        printf("m_tmpSolverBodyPool.capacity() = %i\n",m_tmpSolverBodyPool.capacity());
        printf("m_tmpSolverConstraintPool.capacity() = %i\n",m_tmpSolverConstraintPool.capacity());
        printf("m_tmpSolverFrictionConstraintPool.capacity() = %i\n",m_tmpSolverFrictionConstraintPool.capacity());
*/

        m_tmpSolverBodyPool.resize(0);
        m_tmpSolverConstraintPool.resize(0);
        m_tmpSolverFrictionConstraintPool.resize(0);


        return 0.f;
}

/// btSequentialImpulseConstraintSolver Sequentially applies impulses
btScalar btSequentialImpulseConstraintSolver::solveGroup(btCollisionObject** bodies,int numBodies,btPersistentManifold** manifoldPtr, int numManifolds,btTypedConstraint** constraints,int numConstraints,const btContactSolverInfo& infoGlobal,btIDebugDraw* debugDrawer,btStackAlloc* stackAlloc,btDispatcher* /*dispatcher*/)
{
        BT_PROFILE("solveGroup");
        if (infoGlobal.m_solverMode & SOLVER_CACHE_FRIENDLY)
        {
                //you need to provide at least some bodies
                //btSimpleDynamicsWorld needs to switch off SOLVER_CACHE_FRIENDLY
                btAssert(bodies);
                btAssert(numBodies);
                return solveGroupCacheFriendly(bodies,numBodies,manifoldPtr, numManifolds,constraints,numConstraints,infoGlobal,debugDrawer,stackAlloc);
        }

        

        btContactSolverInfo info = infoGlobal;

        int numiter = infoGlobal.m_numIterations;

        int totalPoints = 0;


        {
                short j;
                for (j=0;j<numManifolds;j++)
                {
                        btPersistentManifold* manifold = manifoldPtr[j];
                        prepareConstraints(manifold,info,debugDrawer);

                        for (short p=0;p<manifoldPtr[j]->getNumContacts();p++)
                        {
                                gOrder[totalPoints].m_manifoldIndex = j;
                                gOrder[totalPoints].m_pointIndex = p;
                                totalPoints++;
                        }
                }
        }

        {
                int j;
                for (j=0;j<numConstraints;j++)
                {
                        btTypedConstraint* constraint = constraints[j];
                        constraint->buildJacobian();
                }
        }
        

        //should traverse the contacts random order...
        int iteration;

        {
                for ( iteration = 0;iteration<numiter;iteration++)
                {
                        int j;
                        if (infoGlobal.m_solverMode & SOLVER_RANDMIZE_ORDER)
                        {
                                if ((iteration & 7) == 0) {
                                        for (j=0; j<totalPoints; ++j) {
                                                btOrderIndex tmp = gOrder[j];
                                                int swapi = btRandInt2(j+1);
                                                gOrder[j] = gOrder[swapi];
                                                gOrder[swapi] = tmp;
                                        }
                                }
                        }

                        for (j=0;j<numConstraints;j++)
                        {
                                btTypedConstraint* constraint = constraints[j];
                                constraint->solveConstraint(info.m_timeStep);
                        }

                        for (j=0;j<totalPoints;j++)
                        {
                                btPersistentManifold* manifold = manifoldPtr[gOrder[j].m_manifoldIndex];
                                solve( (btRigidBody*)manifold->getBody0(),
                                                                        (btRigidBody*)manifold->getBody1()
                                ,manifold->getContactPoint(gOrder[j].m_pointIndex),info,iteration,debugDrawer);
                        }
                
                        for (j=0;j<totalPoints;j++)
                        {
                                btPersistentManifold* manifold = manifoldPtr[gOrder[j].m_manifoldIndex];
                                solveFriction((btRigidBody*)manifold->getBody0(),
                                        (btRigidBody*)manifold->getBody1(),manifold->getContactPoint(gOrder[j].m_pointIndex),info,iteration,debugDrawer);
                        }
                        
                }
        }
                



        return btScalar(0.);
}







void    btSequentialImpulseConstraintSolver::prepareConstraints(btPersistentManifold* manifoldPtr, const btContactSolverInfo& info,btIDebugDraw* debugDrawer)
{

        (void)debugDrawer;

        btRigidBody* body0 = (btRigidBody*)manifoldPtr->getBody0();
        btRigidBody* body1 = (btRigidBody*)manifoldPtr->getBody1();


        //only necessary to refresh the manifold once (first iteration). The integration is done outside the loop
        {
#ifdef FORCE_REFESH_CONTACT_MANIFOLDS
                manifoldPtr->refreshContactPoints(body0->getCenterOfMassTransform(),body1->getCenterOfMassTransform());
#endif //FORCE_REFESH_CONTACT_MANIFOLDS         
                int numpoints = manifoldPtr->getNumContacts();

                gTotalContactPoints += numpoints;

                
                for (int i=0;i<numpoints ;i++)
                {
                        btManifoldPoint& cp = manifoldPtr->getContactPoint(i);
                        if (cp.getDistance() <= btScalar(0.))
                        {
                                const btVector3& pos1 = cp.getPositionWorldOnA();
                                const btVector3& pos2 = cp.getPositionWorldOnB();

                                btVector3 rel_pos1 = pos1 - body0->getCenterOfMassPosition(); 
                                btVector3 rel_pos2 = pos2 - body1->getCenterOfMassPosition();
                                

                                //this jacobian entry is re-used for all iterations
                                btJacobianEntry jac(body0->getCenterOfMassTransform().getBasis().transpose(),
                                        body1->getCenterOfMassTransform().getBasis().transpose(),
                                        rel_pos1,rel_pos2,cp.m_normalWorldOnB,body0->getInvInertiaDiagLocal(),body0->getInvMass(),
                                        body1->getInvInertiaDiagLocal(),body1->getInvMass());

                                
                                btScalar jacDiagAB = jac.getDiagonal();

                                btConstraintPersistentData* cpd = (btConstraintPersistentData*) cp.m_userPersistentData;
                                if (cpd)
                                {
                                        //might be invalid
                                        cpd->m_persistentLifeTime++;
                                        if (cpd->m_persistentLifeTime != cp.getLifeTime())
                                        {
                                                //printf("Invalid: cpd->m_persistentLifeTime = %i cp.getLifeTime() = %i\n",cpd->m_persistentLifeTime,cp.getLifeTime());
                                                new (cpd) btConstraintPersistentData;
                                                cpd->m_persistentLifeTime = cp.getLifeTime();

                                        } else
                                        {
                                                //printf("Persistent: cpd->m_persistentLifeTime = %i cp.getLifeTime() = %i\n",cpd->m_persistentLifeTime,cp.getLifeTime());
                                                
                                        }
                                } else
                                {
                                                
                                        //todo: should this be in a pool?
                                        void* mem = btAlignedAlloc(sizeof(btConstraintPersistentData),16);
                                        cpd = new (mem)btConstraintPersistentData;
                                        assert(cpd);

                                        totalCpd ++;
                                        //printf("totalCpd = %i Created Ptr %x\n",totalCpd,cpd);
                                        cp.m_userPersistentData = cpd;
                                        cpd->m_persistentLifeTime = cp.getLifeTime();
                                        //printf("CREATED: %x . cpd->m_persistentLifeTime = %i cp.getLifeTime() = %i\n",cpd,cpd->m_persistentLifeTime,cp.getLifeTime());
                                        
                                }
                                assert(cpd);

                                cpd->m_jacDiagABInv = btScalar(1.) / jacDiagAB;

                                //Dependent on Rigidbody A and B types, fetch the contact/friction response func
                                //perhaps do a similar thing for friction/restutution combiner funcs...
                                
                                cpd->m_frictionSolverFunc = m_frictionDispatch[body0->m_frictionSolverType][body1->m_frictionSolverType];
                                cpd->m_contactSolverFunc = m_contactDispatch[body0->m_contactSolverType][body1->m_contactSolverType];
                                
                                btVector3 vel1 = body0->getVelocityInLocalPoint(rel_pos1);
                                btVector3 vel2 = body1->getVelocityInLocalPoint(rel_pos2);
                                btVector3 vel = vel1 - vel2;
                                btScalar rel_vel;
                                rel_vel = cp.m_normalWorldOnB.dot(vel);
                                
                                btScalar combinedRestitution = cp.m_combinedRestitution;
                                
                                cpd->m_penetration = cp.getDistance();///btScalar(info.m_numIterations);
                                cpd->m_friction = cp.m_combinedFriction;
                                if (cp.m_lifeTime>info.m_restingContactRestitutionThreshold)
                                {
                                        cpd->m_restitution = 0.f;
                                } else
                                {
                                        cpd->m_restitution = restitutionCurve(rel_vel, combinedRestitution);
                                        if (cpd->m_restitution <= btScalar(0.))
                                        {
                                                cpd->m_restitution = btScalar(0.0);
                                        };
                                }
                                
                                //restitution and penetration work in same direction so
                                //rel_vel 
                                
                                btScalar penVel = -cpd->m_penetration/info.m_timeStep;

                                if (cpd->m_restitution > penVel)
                                {
                                        cpd->m_penetration = btScalar(0.);
                                }                               
                                

                                btScalar relaxation = info.m_damping;
                                if (info.m_solverMode & SOLVER_USE_WARMSTARTING)
                                {
                                        cpd->m_appliedImpulse *= relaxation;
                                } else
                                {
                                        cpd->m_appliedImpulse =btScalar(0.);
                                }
        
                                //for friction
                                cpd->m_prevAppliedImpulse = cpd->m_appliedImpulse;
                                
                                //re-calculate friction direction every frame, todo: check if this is really needed
                                btPlaneSpace1(cp.m_normalWorldOnB,cpd->m_frictionWorldTangential0,cpd->m_frictionWorldTangential1);


#define NO_FRICTION_WARMSTART 1

        #ifdef NO_FRICTION_WARMSTART
                                cpd->m_accumulatedTangentImpulse0 = btScalar(0.);
                                cpd->m_accumulatedTangentImpulse1 = btScalar(0.);
        #endif //NO_FRICTION_WARMSTART
                                btScalar denom0 = body0->computeImpulseDenominator(pos1,cpd->m_frictionWorldTangential0);
                                btScalar denom1 = body1->computeImpulseDenominator(pos2,cpd->m_frictionWorldTangential0);
                                btScalar denom = relaxation/(denom0+denom1);
                                cpd->m_jacDiagABInvTangent0 = denom;


                                denom0 = body0->computeImpulseDenominator(pos1,cpd->m_frictionWorldTangential1);
                                denom1 = body1->computeImpulseDenominator(pos2,cpd->m_frictionWorldTangential1);
                                denom = relaxation/(denom0+denom1);
                                cpd->m_jacDiagABInvTangent1 = denom;

                                btVector3 totalImpulse = 
        #ifndef NO_FRICTION_WARMSTART
                                        cpd->m_frictionWorldTangential0*cpd->m_accumulatedTangentImpulse0+
                                        cpd->m_frictionWorldTangential1*cpd->m_accumulatedTangentImpulse1+
        #endif //NO_FRICTION_WARMSTART
                                        cp.m_normalWorldOnB*cpd->m_appliedImpulse;



                                ///
                                {
                                btVector3 torqueAxis0 = rel_pos1.cross(cp.m_normalWorldOnB);
                                cpd->m_angularComponentA = body0->getInvInertiaTensorWorld()*torqueAxis0;
                                btVector3 torqueAxis1 = rel_pos2.cross(cp.m_normalWorldOnB);            
                                cpd->m_angularComponentB = body1->getInvInertiaTensorWorld()*torqueAxis1;
                                }
                                {
                                        btVector3 ftorqueAxis0 = rel_pos1.cross(cpd->m_frictionWorldTangential0);
                                        cpd->m_frictionAngularComponent0A = body0->getInvInertiaTensorWorld()*ftorqueAxis0;
                                }
                                {
                                        btVector3 ftorqueAxis1 = rel_pos1.cross(cpd->m_frictionWorldTangential1);
                                        cpd->m_frictionAngularComponent1A = body0->getInvInertiaTensorWorld()*ftorqueAxis1;
                                }
                                {
                                        btVector3 ftorqueAxis0 = rel_pos2.cross(cpd->m_frictionWorldTangential0);
                                        cpd->m_frictionAngularComponent0B = body1->getInvInertiaTensorWorld()*ftorqueAxis0;
                                }
                                {
                                        btVector3 ftorqueAxis1 = rel_pos2.cross(cpd->m_frictionWorldTangential1);
                                        cpd->m_frictionAngularComponent1B = body1->getInvInertiaTensorWorld()*ftorqueAxis1;
                                }
                                
                                ///



                                //apply previous frames impulse on both bodies
                                body0->applyImpulse(totalImpulse, rel_pos1);
                                body1->applyImpulse(-totalImpulse, rel_pos2);
                        }
                        
                }
        }
}


btScalar btSequentialImpulseConstraintSolver::solveCombinedContactFriction(btRigidBody* body0,btRigidBody* body1, btManifoldPoint& cp, const btContactSolverInfo& info,int iter,btIDebugDraw* debugDrawer)
{
        btScalar maxImpulse = btScalar(0.);

        {

                
                {
                        if (cp.getDistance() <= btScalar(0.))
                        {

                                

                                {

                                        //btConstraintPersistentData* cpd = (btConstraintPersistentData*) cp.m_userPersistentData;
                                        btScalar impulse = resolveSingleCollisionCombined(
                                                *body0,*body1,
                                                cp,
                                                info);

                                        if (maxImpulse < impulse)
                                                maxImpulse  = impulse;

                                }
                        }
                }
        }
        return maxImpulse;
}



btScalar btSequentialImpulseConstraintSolver::solve(btRigidBody* body0,btRigidBody* body1, btManifoldPoint& cp, const btContactSolverInfo& info,int iter,btIDebugDraw* debugDrawer)
{

        btScalar maxImpulse = btScalar(0.);

        {

                
                {
                        if (cp.getDistance() <= btScalar(0.))
                        {

                                

                                {

                                        btConstraintPersistentData* cpd = (btConstraintPersistentData*) cp.m_userPersistentData;
                                        btScalar impulse = cpd->m_contactSolverFunc(
                                                *body0,*body1,
                                                cp,
                                                info);

                                        if (maxImpulse < impulse)
                                                maxImpulse  = impulse;

                                }
                        }
                }
        }
        return maxImpulse;
}

btScalar btSequentialImpulseConstraintSolver::solveFriction(btRigidBody* body0,btRigidBody* body1, btManifoldPoint& cp, const btContactSolverInfo& info,int iter,btIDebugDraw* debugDrawer)
{

        (void)debugDrawer;
        (void)iter;


        {

                
                {
                        
                        if (cp.getDistance() <= btScalar(0.))
                        {

                                btConstraintPersistentData* cpd = (btConstraintPersistentData*) cp.m_userPersistentData;
                                cpd->m_frictionSolverFunc(
                                        *body0,*body1,
                                        cp,
                                        info);

                                
                        }
                }

        
        }
        return btScalar(0.);
}


void    btSequentialImpulseConstraintSolver::reset()
{
        m_btSeed2 = 0;
}