source: code/trunk/src/external/bullet/BulletDynamics/ConstraintSolver/btGeneric6DofConstraint.cpp @ 7561

/*
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.
*/
/*
2007-09-09
Refactored by Francisco Le?n
email: projectileman@yahoo.com
http://gimpact.sf.net
*/

#include "btGeneric6DofConstraint.h"
#include "BulletDynamics/Dynamics/btRigidBody.h"
#include "LinearMath/btTransformUtil.h"
#include <new>


#define D6_USE_OBSOLETE_METHOD false
//-----------------------------------------------------------------------------

btGeneric6DofConstraint::btGeneric6DofConstraint()
:btTypedConstraint(D6_CONSTRAINT_TYPE),
m_useLinearReferenceFrameA(true),
m_useSolveConstraintObsolete(D6_USE_OBSOLETE_METHOD)
{
}

//-----------------------------------------------------------------------------

btGeneric6DofConstraint::btGeneric6DofConstraint(btRigidBody& rbA, btRigidBody& rbB, const btTransform& frameInA, const btTransform& frameInB, bool useLinearReferenceFrameA)
: btTypedConstraint(D6_CONSTRAINT_TYPE, rbA, rbB)
, m_frameInA(frameInA)
, m_frameInB(frameInB),
m_useLinearReferenceFrameA(useLinearReferenceFrameA),
m_useSolveConstraintObsolete(D6_USE_OBSOLETE_METHOD)
{

}
//-----------------------------------------------------------------------------


#define GENERIC_D6_DISABLE_WARMSTARTING 1

//-----------------------------------------------------------------------------

btScalar btGetMatrixElem(const btMatrix3x3& mat, int index);
btScalar btGetMatrixElem(const btMatrix3x3& mat, int index)
{
        int i = index%3;
        int j = index/3;
        return mat[i][j];
}

//-----------------------------------------------------------------------------

///MatrixToEulerXYZ from http://www.geometrictools.com/LibFoundation/Mathematics/Wm4Matrix3.inl.html
bool    matrixToEulerXYZ(const btMatrix3x3& mat,btVector3& xyz);
bool    matrixToEulerXYZ(const btMatrix3x3& mat,btVector3& xyz)
{
        //      // rot =  cy*cz          -cy*sz           sy
        //      //        cz*sx*sy+cx*sz  cx*cz-sx*sy*sz -cy*sx
        //      //       -cx*cz*sy+sx*sz  cz*sx+cx*sy*sz  cx*cy
        //

        btScalar fi = btGetMatrixElem(mat,2);
        if (fi < btScalar(1.0f))
        {
                if (fi > btScalar(-1.0f))
                {
                        xyz[0] = btAtan2(-btGetMatrixElem(mat,5),btGetMatrixElem(mat,8));
                        xyz[1] = btAsin(btGetMatrixElem(mat,2));
                        xyz[2] = btAtan2(-btGetMatrixElem(mat,1),btGetMatrixElem(mat,0));
                        return true;
                }
                else
                {
                        // WARNING.  Not unique.  XA - ZA = -atan2(r10,r11)
                        xyz[0] = -btAtan2(btGetMatrixElem(mat,3),btGetMatrixElem(mat,4));
                        xyz[1] = -SIMD_HALF_PI;
                        xyz[2] = btScalar(0.0);
                        return false;
                }
        }
        else
        {
                // WARNING.  Not unique.  XAngle + ZAngle = atan2(r10,r11)
                xyz[0] = btAtan2(btGetMatrixElem(mat,3),btGetMatrixElem(mat,4));
                xyz[1] = SIMD_HALF_PI;
                xyz[2] = 0.0;
        }
        return false;
}

//////////////////////////// btRotationalLimitMotor ////////////////////////////////////

int btRotationalLimitMotor::testLimitValue(btScalar test_value)
{
        if(m_loLimit>m_hiLimit)
        {
                m_currentLimit = 0;//Free from violation
                return 0;
        }

        if (test_value < m_loLimit)
        {
                m_currentLimit = 1;//low limit violation
                m_currentLimitError =  test_value - m_loLimit;
                return 1;
        }
        else if (test_value> m_hiLimit)
        {
                m_currentLimit = 2;//High limit violation
                m_currentLimitError = test_value - m_hiLimit;
                return 2;
        };

        m_currentLimit = 0;//Free from violation
        return 0;

}

//-----------------------------------------------------------------------------

btScalar btRotationalLimitMotor::solveAngularLimits(
        btScalar timeStep,btVector3& axis,btScalar jacDiagABInv,
        btRigidBody * body0, btSolverBody& bodyA, btRigidBody * body1, btSolverBody& bodyB)
{
        if (needApplyTorques()==false) return 0.0f;

        btScalar target_velocity = m_targetVelocity;
        btScalar maxMotorForce = m_maxMotorForce;

        //current error correction
        if (m_currentLimit!=0)
        {
                target_velocity = -m_ERP*m_currentLimitError/(timeStep);
                maxMotorForce = m_maxLimitForce;
        }

        maxMotorForce *= timeStep;

        // current velocity difference

        btVector3 angVelA;
        bodyA.getAngularVelocity(angVelA);
        btVector3 angVelB;
        bodyB.getAngularVelocity(angVelB);

        btVector3 vel_diff;
        vel_diff = angVelA-angVelB;



        btScalar rel_vel = axis.dot(vel_diff);

        // correction velocity
        btScalar motor_relvel = m_limitSoftness*(target_velocity  - m_damping*rel_vel);


        if ( motor_relvel < SIMD_EPSILON && motor_relvel > -SIMD_EPSILON  )
        {
                return 0.0f;//no need for applying force
        }


        // correction impulse
        btScalar unclippedMotorImpulse = (1+m_bounce)*motor_relvel*jacDiagABInv;

        // clip correction impulse
        btScalar clippedMotorImpulse;

        ///@todo: should clip against accumulated impulse
        if (unclippedMotorImpulse>0.0f)
        {
                clippedMotorImpulse =  unclippedMotorImpulse > maxMotorForce? maxMotorForce: unclippedMotorImpulse;
        }
        else
        {
                clippedMotorImpulse =  unclippedMotorImpulse < -maxMotorForce ? -maxMotorForce: unclippedMotorImpulse;
        }


        // sort with accumulated impulses
        btScalar        lo = btScalar(-1e30);
        btScalar        hi = btScalar(1e30);

        btScalar oldaccumImpulse = m_accumulatedImpulse;
        btScalar sum = oldaccumImpulse + clippedMotorImpulse;
        m_accumulatedImpulse = sum > hi ? btScalar(0.) : sum < lo ? btScalar(0.) : sum;

        clippedMotorImpulse = m_accumulatedImpulse - oldaccumImpulse;

        btVector3 motorImp = clippedMotorImpulse * axis;

        //body0->applyTorqueImpulse(motorImp);
        //body1->applyTorqueImpulse(-motorImp);

        bodyA.applyImpulse(btVector3(0,0,0), body0->getInvInertiaTensorWorld()*axis,clippedMotorImpulse);
        bodyB.applyImpulse(btVector3(0,0,0), body1->getInvInertiaTensorWorld()*axis,-clippedMotorImpulse);


        return clippedMotorImpulse;


}

//////////////////////////// End btRotationalLimitMotor ////////////////////////////////////




//////////////////////////// btTranslationalLimitMotor ////////////////////////////////////


int btTranslationalLimitMotor::testLimitValue(int limitIndex, btScalar test_value)
{
        btScalar loLimit = m_lowerLimit[limitIndex];
        btScalar hiLimit = m_upperLimit[limitIndex];
        if(loLimit > hiLimit)
        {
                m_currentLimit[limitIndex] = 0;//Free from violation
                m_currentLimitError[limitIndex] = btScalar(0.f);
                return 0;
        }

        if (test_value < loLimit)
        {
                m_currentLimit[limitIndex] = 2;//low limit violation
                m_currentLimitError[limitIndex] =  test_value - loLimit;
                return 2;
        }
        else if (test_value> hiLimit)
        {
                m_currentLimit[limitIndex] = 1;//High limit violation
                m_currentLimitError[limitIndex] = test_value - hiLimit;
                return 1;
        };

        m_currentLimit[limitIndex] = 0;//Free from violation
        m_currentLimitError[limitIndex] = btScalar(0.f);
        return 0;
} // btTranslationalLimitMotor::testLimitValue()

//-----------------------------------------------------------------------------

btScalar btTranslationalLimitMotor::solveLinearAxis(
        btScalar timeStep,
        btScalar jacDiagABInv,
        btRigidBody& body1,btSolverBody& bodyA,const btVector3 &pointInA,
        btRigidBody& body2,btSolverBody& bodyB,const btVector3 &pointInB,
        int limit_index,
        const btVector3 & axis_normal_on_a,
        const btVector3 & anchorPos)
{

        ///find relative velocity
        //    btVector3 rel_pos1 = pointInA - body1.getCenterOfMassPosition();
        //    btVector3 rel_pos2 = pointInB - body2.getCenterOfMassPosition();
        btVector3 rel_pos1 = anchorPos - body1.getCenterOfMassPosition();
        btVector3 rel_pos2 = anchorPos - body2.getCenterOfMassPosition();

        btVector3 vel1;
        bodyA.getVelocityInLocalPointObsolete(rel_pos1,vel1);
        btVector3 vel2;
        bodyB.getVelocityInLocalPointObsolete(rel_pos2,vel2);
        btVector3 vel = vel1 - vel2;

        btScalar rel_vel = axis_normal_on_a.dot(vel);



        /// apply displacement correction

        //positional error (zeroth order error)
        btScalar depth = -(pointInA - pointInB).dot(axis_normal_on_a);
        btScalar        lo = btScalar(-1e30);
        btScalar        hi = btScalar(1e30);

        btScalar minLimit = m_lowerLimit[limit_index];
        btScalar maxLimit = m_upperLimit[limit_index];

        //handle the limits
        if (minLimit < maxLimit)
        {
                {
                        if (depth > maxLimit)
                        {
                                depth -= maxLimit;
                                lo = btScalar(0.);

                        }
                        else
                        {
                                if (depth < minLimit)
                                {
                                        depth -= minLimit;
                                        hi = btScalar(0.);
                                }
                                else
                                {
                                        return 0.0f;
                                }
                        }
                }
        }

        btScalar normalImpulse= m_limitSoftness*(m_restitution*depth/timeStep - m_damping*rel_vel) * jacDiagABInv;




        btScalar oldNormalImpulse = m_accumulatedImpulse[limit_index];
        btScalar sum = oldNormalImpulse + normalImpulse;
        m_accumulatedImpulse[limit_index] = sum > hi ? btScalar(0.) : sum < lo ? btScalar(0.) : sum;
        normalImpulse = m_accumulatedImpulse[limit_index] - oldNormalImpulse;

        btVector3 impulse_vector = axis_normal_on_a * normalImpulse;
        //body1.applyImpulse( impulse_vector, rel_pos1);
        //body2.applyImpulse(-impulse_vector, rel_pos2);

        btVector3 ftorqueAxis1 = rel_pos1.cross(axis_normal_on_a);
        btVector3 ftorqueAxis2 = rel_pos2.cross(axis_normal_on_a);
        bodyA.applyImpulse(axis_normal_on_a*body1.getInvMass(), body1.getInvInertiaTensorWorld()*ftorqueAxis1,normalImpulse);
        bodyB.applyImpulse(axis_normal_on_a*body2.getInvMass(), body2.getInvInertiaTensorWorld()*ftorqueAxis2,-normalImpulse);




        return normalImpulse;
}

//////////////////////////// btTranslationalLimitMotor ////////////////////////////////////

void btGeneric6DofConstraint::calculateAngleInfo()
{
        btMatrix3x3 relative_frame = m_calculatedTransformA.getBasis().inverse()*m_calculatedTransformB.getBasis();
        matrixToEulerXYZ(relative_frame,m_calculatedAxisAngleDiff);
        // in euler angle mode we do not actually constrain the angular velocity
        // along the axes axis[0] and axis[2] (although we do use axis[1]) :
        //
        //    to get                    constrain w2-w1 along           ...not
        //    ------                    ---------------------           ------
        //    d(angle[0])/dt = 0        ax[1] x ax[2]                   ax[0]
        //    d(angle[1])/dt = 0        ax[1]
        //    d(angle[2])/dt = 0        ax[0] x ax[1]                   ax[2]
        //
        // constraining w2-w1 along an axis 'a' means that a'*(w2-w1)=0.
        // to prove the result for angle[0], write the expression for angle[0] from
        // GetInfo1 then take the derivative. to prove this for angle[2] it is
        // easier to take the euler rate expression for d(angle[2])/dt with respect
        // to the components of w and set that to 0.
        btVector3 axis0 = m_calculatedTransformB.getBasis().getColumn(0);
        btVector3 axis2 = m_calculatedTransformA.getBasis().getColumn(2);

        m_calculatedAxis[1] = axis2.cross(axis0);
        m_calculatedAxis[0] = m_calculatedAxis[1].cross(axis2);
        m_calculatedAxis[2] = axis0.cross(m_calculatedAxis[1]);

        m_calculatedAxis[0].normalize();
        m_calculatedAxis[1].normalize();
        m_calculatedAxis[2].normalize();

}

//-----------------------------------------------------------------------------

void btGeneric6DofConstraint::calculateTransforms()
{
        m_calculatedTransformA = m_rbA.getCenterOfMassTransform() * m_frameInA;
        m_calculatedTransformB = m_rbB.getCenterOfMassTransform() * m_frameInB;
        calculateLinearInfo();
        calculateAngleInfo();
}

//-----------------------------------------------------------------------------

void btGeneric6DofConstraint::buildLinearJacobian(
        btJacobianEntry & jacLinear,const btVector3 & normalWorld,
        const btVector3 & pivotAInW,const btVector3 & pivotBInW)
{
        new (&jacLinear) btJacobianEntry(
        m_rbA.getCenterOfMassTransform().getBasis().transpose(),
        m_rbB.getCenterOfMassTransform().getBasis().transpose(),
        pivotAInW - m_rbA.getCenterOfMassPosition(),
        pivotBInW - m_rbB.getCenterOfMassPosition(),
        normalWorld,
        m_rbA.getInvInertiaDiagLocal(),
        m_rbA.getInvMass(),
        m_rbB.getInvInertiaDiagLocal(),
        m_rbB.getInvMass());
}

//-----------------------------------------------------------------------------

void btGeneric6DofConstraint::buildAngularJacobian(
        btJacobianEntry & jacAngular,const btVector3 & jointAxisW)
{
         new (&jacAngular)      btJacobianEntry(jointAxisW,
                                      m_rbA.getCenterOfMassTransform().getBasis().transpose(),
                                      m_rbB.getCenterOfMassTransform().getBasis().transpose(),
                                      m_rbA.getInvInertiaDiagLocal(),
                                      m_rbB.getInvInertiaDiagLocal());

}

//-----------------------------------------------------------------------------

bool btGeneric6DofConstraint::testAngularLimitMotor(int axis_index)
{
        btScalar angle = m_calculatedAxisAngleDiff[axis_index];
        //test limits
        m_angularLimits[axis_index].testLimitValue(angle);
        return m_angularLimits[axis_index].needApplyTorques();
}

//-----------------------------------------------------------------------------

void btGeneric6DofConstraint::buildJacobian()
{
        if (m_useSolveConstraintObsolete)
        {

                // Clear accumulated impulses for the next simulation step
                m_linearLimits.m_accumulatedImpulse.setValue(btScalar(0.), btScalar(0.), btScalar(0.));
                int i;
                for(i = 0; i < 3; i++)
                {
                        m_angularLimits[i].m_accumulatedImpulse = btScalar(0.);
                }
                //calculates transform
                calculateTransforms();

                //  const btVector3& pivotAInW = m_calculatedTransformA.getOrigin();
                //  const btVector3& pivotBInW = m_calculatedTransformB.getOrigin();
                calcAnchorPos();
                btVector3 pivotAInW = m_AnchorPos;
                btVector3 pivotBInW = m_AnchorPos;

                // not used here
                //    btVector3 rel_pos1 = pivotAInW - m_rbA.getCenterOfMassPosition();
                //    btVector3 rel_pos2 = pivotBInW - m_rbB.getCenterOfMassPosition();

                btVector3 normalWorld;
                //linear part
                for (i=0;i<3;i++)
                {
                        if (m_linearLimits.isLimited(i))
                        {
                                if (m_useLinearReferenceFrameA)
                                        normalWorld = m_calculatedTransformA.getBasis().getColumn(i);
                                else
                                        normalWorld = m_calculatedTransformB.getBasis().getColumn(i);

                                buildLinearJacobian(
                                        m_jacLinear[i],normalWorld ,
                                        pivotAInW,pivotBInW);

                        }
                }

                // angular part
                for (i=0;i<3;i++)
                {
                        //calculates error angle
                        if (testAngularLimitMotor(i))
                        {
                                normalWorld = this->getAxis(i);
                                // Create angular atom
                                buildAngularJacobian(m_jacAng[i],normalWorld);
                        }
                }

        }
}

//-----------------------------------------------------------------------------

void btGeneric6DofConstraint::getInfo1 (btConstraintInfo1* info)
{
        if (m_useSolveConstraintObsolete)
        {
                info->m_numConstraintRows = 0;
                info->nub = 0;
        } else
        {
                //prepare constraint
                calculateTransforms();
                info->m_numConstraintRows = 0;
                info->nub = 6;
                int i;
                //test linear limits
                for(i = 0; i < 3; i++)
                {
                        if(m_linearLimits.needApplyForce(i))
                        {
                                info->m_numConstraintRows++;
                                info->nub--;
                        }
                }
                //test angular limits
                for (i=0;i<3 ;i++ )
                {
                        if(testAngularLimitMotor(i))
                        {
                                info->m_numConstraintRows++;
                                info->nub--;
                        }
                }
        }
}

//-----------------------------------------------------------------------------

void btGeneric6DofConstraint::getInfo2 (btConstraintInfo2* info)
{
        btAssert(!m_useSolveConstraintObsolete);
        int row = setLinearLimits(info);
        setAngularLimits(info, row);
}

//-----------------------------------------------------------------------------

int btGeneric6DofConstraint::setLinearLimits(btConstraintInfo2* info)
{
        btGeneric6DofConstraint * d6constraint = this;
        int row = 0;
        //solve linear limits
        btRotationalLimitMotor limot;
        for (int i=0;i<3 ;i++ )
        {
                if(m_linearLimits.needApplyForce(i))
                { // re-use rotational motor code
                        limot.m_bounce = btScalar(0.f);
                        limot.m_currentLimit = m_linearLimits.m_currentLimit[i];
                        limot.m_currentLimitError  = m_linearLimits.m_currentLimitError[i];
                        limot.m_damping  = m_linearLimits.m_damping;
                        limot.m_enableMotor  = m_linearLimits.m_enableMotor[i];
                        limot.m_ERP  = m_linearLimits.m_restitution;
                        limot.m_hiLimit  = m_linearLimits.m_upperLimit[i];
                        limot.m_limitSoftness  = m_linearLimits.m_limitSoftness;
                        limot.m_loLimit  = m_linearLimits.m_lowerLimit[i];
                        limot.m_maxLimitForce  = btScalar(0.f);
                        limot.m_maxMotorForce  = m_linearLimits.m_maxMotorForce[i];
                        limot.m_targetVelocity  = m_linearLimits.m_targetVelocity[i];
                        btVector3 axis = m_calculatedTransformA.getBasis().getColumn(i);
                        row += get_limit_motor_info2(&limot, &m_rbA, &m_rbB, info, row, axis, 0);
                }
        }
        return row;
}

//-----------------------------------------------------------------------------

int btGeneric6DofConstraint::setAngularLimits(btConstraintInfo2 *info, int row_offset)
{
        btGeneric6DofConstraint * d6constraint = this;
        int row = row_offset;
        //solve angular limits
        for (int i=0;i<3 ;i++ )
        {
                if(d6constraint->getRotationalLimitMotor(i)->needApplyTorques())
                {
                        btVector3 axis = d6constraint->getAxis(i);
                        row += get_limit_motor_info2(
                                d6constraint->getRotationalLimitMotor(i),
                                &m_rbA,
                                &m_rbB,
                                info,row,axis,1);
                }
        }

        return row;
}

//-----------------------------------------------------------------------------

void btGeneric6DofConstraint::solveConstraintObsolete(btSolverBody& bodyA,btSolverBody& bodyB,btScalar  timeStep)
{
        if (m_useSolveConstraintObsolete)
        {


                m_timeStep = timeStep;

                //calculateTransforms();

                int i;

                // linear

                btVector3 pointInA = m_calculatedTransformA.getOrigin();
                btVector3 pointInB = m_calculatedTransformB.getOrigin();

                btScalar jacDiagABInv;
                btVector3 linear_axis;
                for (i=0;i<3;i++)
                {
                        if (m_linearLimits.isLimited(i))
                        {
                                jacDiagABInv = btScalar(1.) / m_jacLinear[i].getDiagonal();

                                if (m_useLinearReferenceFrameA)
                                        linear_axis = m_calculatedTransformA.getBasis().getColumn(i);
                                else
                                        linear_axis = m_calculatedTransformB.getBasis().getColumn(i);

                                m_linearLimits.solveLinearAxis(
                                        m_timeStep,
                                        jacDiagABInv,
                                        m_rbA,bodyA,pointInA,
                                        m_rbB,bodyB,pointInB,
                                        i,linear_axis, m_AnchorPos);

                        }
                }

                // angular
                btVector3 angular_axis;
                btScalar angularJacDiagABInv;
                for (i=0;i<3;i++)
                {
                        if (m_angularLimits[i].needApplyTorques())
                        {

                                // get axis
                                angular_axis = getAxis(i);

                                angularJacDiagABInv = btScalar(1.) / m_jacAng[i].getDiagonal();

                                m_angularLimits[i].solveAngularLimits(m_timeStep,angular_axis,angularJacDiagABInv, &m_rbA,bodyA,&m_rbB,bodyB);
                        }
                }
        }
}

//-----------------------------------------------------------------------------

void    btGeneric6DofConstraint::updateRHS(btScalar     timeStep)
{
        (void)timeStep;

}

//-----------------------------------------------------------------------------

btVector3 btGeneric6DofConstraint::getAxis(int axis_index) const
{
        return m_calculatedAxis[axis_index];
}

//-----------------------------------------------------------------------------

btScalar btGeneric6DofConstraint::getAngle(int axis_index) const
{
        return m_calculatedAxisAngleDiff[axis_index];
}

//-----------------------------------------------------------------------------

void btGeneric6DofConstraint::calcAnchorPos(void)
{
        btScalar imA = m_rbA.getInvMass();
        btScalar imB = m_rbB.getInvMass();
        btScalar weight;
        if(imB == btScalar(0.0))
        {
                weight = btScalar(1.0);
        }
        else
        {
                weight = imA / (imA + imB);
        }
        const btVector3& pA = m_calculatedTransformA.getOrigin();
        const btVector3& pB = m_calculatedTransformB.getOrigin();
        m_AnchorPos = pA * weight + pB * (btScalar(1.0) - weight);
        return;
} // btGeneric6DofConstraint::calcAnchorPos()

//-----------------------------------------------------------------------------

void btGeneric6DofConstraint::calculateLinearInfo()
{
        m_calculatedLinearDiff = m_calculatedTransformB.getOrigin() - m_calculatedTransformA.getOrigin();
        m_calculatedLinearDiff = m_calculatedTransformA.getBasis().inverse() * m_calculatedLinearDiff;
        for(int i = 0; i < 3; i++)
        {
                m_linearLimits.testLimitValue(i, m_calculatedLinearDiff[i]);
        }
} // btGeneric6DofConstraint::calculateLinearInfo()

//-----------------------------------------------------------------------------

int btGeneric6DofConstraint::get_limit_motor_info2(
        btRotationalLimitMotor * limot,
        btRigidBody * body0, btRigidBody * body1,
        btConstraintInfo2 *info, int row, btVector3& ax1, int rotational)
{
    int srow = row * info->rowskip;
    int powered = limot->m_enableMotor;
    int limit = limot->m_currentLimit;
    if (powered || limit)
    {   // if the joint is powered, or has joint limits, add in the extra row
        btScalar *J1 = rotational ? info->m_J1angularAxis : info->m_J1linearAxis;
        btScalar *J2 = rotational ? info->m_J2angularAxis : 0;
        J1[srow+0] = ax1[0];
        J1[srow+1] = ax1[1];
        J1[srow+2] = ax1[2];
        if(rotational)
        {
            J2[srow+0] = -ax1[0];
            J2[srow+1] = -ax1[1];
            J2[srow+2] = -ax1[2];
        }
        if((!rotational) && limit)
        {
                        btVector3 ltd;  // Linear Torque Decoupling vector
                        btVector3 c = m_calculatedTransformB.getOrigin() - body0->getCenterOfMassPosition();
                        ltd = c.cross(ax1);
            info->m_J1angularAxis[srow+0] = ltd[0];
            info->m_J1angularAxis[srow+1] = ltd[1];
            info->m_J1angularAxis[srow+2] = ltd[2];

                        c = m_calculatedTransformB.getOrigin() - body1->getCenterOfMassPosition();
                        ltd = -c.cross(ax1);
                        info->m_J2angularAxis[srow+0] = ltd[0];
            info->m_J2angularAxis[srow+1] = ltd[1];
            info->m_J2angularAxis[srow+2] = ltd[2];
        }
        // if we're limited low and high simultaneously, the joint motor is
        // ineffective
        if (limit && (limot->m_loLimit == limot->m_hiLimit)) powered = 0;
        info->m_constraintError[srow] = btScalar(0.f);
        if (powered)
        {
            info->cfm[srow] = 0.0f;
            if(!limit)
            {
                info->m_constraintError[srow] += limot->m_targetVelocity;
                info->m_lowerLimit[srow] = -limot->m_maxMotorForce;
                info->m_upperLimit[srow] = limot->m_maxMotorForce;
            }
        }
        if(limit)
        {
            btScalar k = info->fps * limot->m_ERP;
                        if(!rotational)
                        {
                                info->m_constraintError[srow] += k * limot->m_currentLimitError;
                        }
                        else
                        {
                                info->m_constraintError[srow] += -k * limot->m_currentLimitError;
                        }
            info->cfm[srow] = 0.0f;
            if (limot->m_loLimit == limot->m_hiLimit)
            {   // limited low and high simultaneously
                info->m_lowerLimit[srow] = -SIMD_INFINITY;
                info->m_upperLimit[srow] = SIMD_INFINITY;
            }
            else
            {
                if (limit == 1)
                {
                    info->m_lowerLimit[srow] = 0;
                    info->m_upperLimit[srow] = SIMD_INFINITY;
                }
                else
                {
                    info->m_lowerLimit[srow] = -SIMD_INFINITY;
                    info->m_upperLimit[srow] = 0;
                }
                // deal with bounce
                if (limot->m_bounce > 0)
                {
                    // calculate joint velocity
                    btScalar vel;
                    if (rotational)
                    {
                        vel = body0->getAngularVelocity().dot(ax1);
                        if (body1)
                            vel -= body1->getAngularVelocity().dot(ax1);
                    }
                    else
                    {
                        vel = body0->getLinearVelocity().dot(ax1);
                        if (body1)
                            vel -= body1->getLinearVelocity().dot(ax1);
                    }
                    // only apply bounce if the velocity is incoming, and if the
                    // resulting c[] exceeds what we already have.
                    if (limit == 1)
                    {
                        if (vel < 0)
                        {
                            btScalar newc = -limot->m_bounce* vel;
                            if (newc > info->m_constraintError[srow]) 
                                                                info->m_constraintError[srow] = newc;
                        }
                    }
                    else
                    {
                        if (vel > 0)
                        {
                            btScalar newc = -limot->m_bounce * vel;
                            if (newc < info->m_constraintError[srow]) 
                                                                info->m_constraintError[srow] = newc;
                        }
                    }
                }
            }
        }
        return 1;
    }
    else return 0;
}

//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------