btRaycastVehicle.cpp

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/*
 * Copyright (c) 2005 Erwin Coumans http://continuousphysics.com/Bullet/
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies.
 * Erwin Coumans makes no representations about the suitability 
 * of this software for any purpose.  
 * It is provided "as is" without express or implied warranty.
*/

#include "LinearMath/btVector3.h"
#include "btRaycastVehicle.h"

#include "BulletDynamics/ConstraintSolver/btSolve2LinearConstraint.h"
#include "BulletDynamics/ConstraintSolver/btJacobianEntry.h"
#include "LinearMath/btQuaternion.h"
#include "BulletDynamics/Dynamics/btDynamicsWorld.h"
#include "btVehicleRaycaster.h"
#include "btWheelInfo.h"
#include "LinearMath/btMinMax.h"
#include "LinearMath/btIDebugDraw.h"
#include "BulletDynamics/ConstraintSolver/btContactConstraint.h"

#define ROLLING_INFLUENCE_FIX


btRigidBody& btActionInterface::getFixedBody()
{
    static btRigidBody s_fixed(0, 0,0);
    s_fixed.setMassProps(btScalar(0.),btVector3(btScalar(0.),btScalar(0.),btScalar(0.)));
    return s_fixed;
}

btRaycastVehicle::btRaycastVehicle(const btVehicleTuning& tuning,btRigidBody* chassis,  btVehicleRaycaster* raycaster )
:m_vehicleRaycaster(raycaster),
m_pitchControl(btScalar(0.))
{
    m_chassisBody = chassis;
    m_indexRightAxis = 0;
    m_indexUpAxis = 2;
    m_indexForwardAxis = 1;
    defaultInit(tuning);
}


void btRaycastVehicle::defaultInit(const btVehicleTuning& tuning)
{
    (void)tuning;
    m_currentVehicleSpeedKmHour = btScalar(0.);
    m_steeringValue = btScalar(0.);
    
}

    

btRaycastVehicle::~btRaycastVehicle()
{
}


//
// basically most of the code is general for 2 or 4 wheel vehicles, but some of it needs to be reviewed
//
btWheelInfo&    btRaycastVehicle::addWheel( const btVector3& connectionPointCS, const btVector3& wheelDirectionCS0,const btVector3& wheelAxleCS, btScalar suspensionRestLength, btScalar wheelRadius,const btVehicleTuning& tuning, bool isFrontWheel)
{

    btWheelInfoConstructionInfo ci;

    ci.m_chassisConnectionCS = connectionPointCS;
    ci.m_wheelDirectionCS = wheelDirectionCS0;
    ci.m_wheelAxleCS = wheelAxleCS;
    ci.m_suspensionRestLength = suspensionRestLength;
    ci.m_wheelRadius = wheelRadius;
    ci.m_suspensionStiffness = tuning.m_suspensionStiffness;
    ci.m_wheelsDampingCompression = tuning.m_suspensionCompression;
    ci.m_wheelsDampingRelaxation = tuning.m_suspensionDamping;
    ci.m_frictionSlip = tuning.m_frictionSlip;
    ci.m_bIsFrontWheel = isFrontWheel;
    ci.m_maxSuspensionTravelCm = tuning.m_maxSuspensionTravelCm;
    ci.m_maxSuspensionForce = tuning.m_maxSuspensionForce;

    m_wheelInfo.push_back( btWheelInfo(ci));
    
    btWheelInfo& wheel = m_wheelInfo[getNumWheels()-1];
    
    updateWheelTransformsWS( wheel , false );
    updateWheelTransform(getNumWheels()-1,false);
    return wheel;
}




const btTransform&  btRaycastVehicle::getWheelTransformWS( int wheelIndex ) const
{
    btAssert(wheelIndex < getNumWheels());
    const btWheelInfo& wheel = m_wheelInfo[wheelIndex];
    return wheel.m_worldTransform;

}

void    btRaycastVehicle::updateWheelTransform( int wheelIndex , bool interpolatedTransform)
{
    
    btWheelInfo& wheel = m_wheelInfo[ wheelIndex ];
    updateWheelTransformsWS(wheel,interpolatedTransform);
    btVector3 up = -wheel.m_raycastInfo.m_wheelDirectionWS;
    const btVector3& right = wheel.m_raycastInfo.m_wheelAxleWS;
    btVector3 fwd = up.cross(right);
    fwd = fwd.normalize();
//  up = right.cross(fwd);
//  up.normalize();

    //rotate around steering over de wheelAxleWS
    btScalar steering = wheel.m_steering;
    
    btQuaternion steeringOrn(up,steering);//wheel.m_steering);
    btMatrix3x3 steeringMat(steeringOrn);

    btQuaternion rotatingOrn(right,-wheel.m_rotation);
    btMatrix3x3 rotatingMat(rotatingOrn);

    btMatrix3x3 basis2(
        right[0],fwd[0],up[0],
        right[1],fwd[1],up[1],
        right[2],fwd[2],up[2]
    );
    
    wheel.m_worldTransform.setBasis(steeringMat * rotatingMat * basis2);
    wheel.m_worldTransform.setOrigin(
        wheel.m_raycastInfo.m_hardPointWS + wheel.m_raycastInfo.m_wheelDirectionWS * wheel.m_raycastInfo.m_suspensionLength
    );
}

void btRaycastVehicle::resetSuspension()
{

    int i;
    for (i=0;i<m_wheelInfo.size();  i++)
    {
            btWheelInfo& wheel = m_wheelInfo[i];
            wheel.m_raycastInfo.m_suspensionLength = wheel.getSuspensionRestLength();
            wheel.m_suspensionRelativeVelocity = btScalar(0.0);
            
            wheel.m_raycastInfo.m_contactNormalWS = - wheel.m_raycastInfo.m_wheelDirectionWS;
            //wheel_info.setContactFriction(btScalar(0.0));
            wheel.m_clippedInvContactDotSuspension = btScalar(1.0);
    }
}

void    btRaycastVehicle::updateWheelTransformsWS(btWheelInfo& wheel , bool interpolatedTransform)
{
    wheel.m_raycastInfo.m_isInContact = false;

    btTransform chassisTrans = getChassisWorldTransform();
    if (interpolatedTransform && (getRigidBody()->getMotionState()))
    {
        getRigidBody()->getMotionState()->getWorldTransform(chassisTrans);
    }

    wheel.m_raycastInfo.m_hardPointWS = chassisTrans( wheel.m_chassisConnectionPointCS );
    wheel.m_raycastInfo.m_wheelDirectionWS = chassisTrans.getBasis() *  wheel.m_wheelDirectionCS ;
    wheel.m_raycastInfo.m_wheelAxleWS = chassisTrans.getBasis() * wheel.m_wheelAxleCS;
}

btScalar btRaycastVehicle::rayCast(btWheelInfo& wheel)
{
    updateWheelTransformsWS( wheel,false);

    
    btScalar depth = -1;
    
    btScalar raylen = wheel.getSuspensionRestLength()+wheel.m_wheelsRadius;

    btVector3 rayvector = wheel.m_raycastInfo.m_wheelDirectionWS * (raylen);
    const btVector3& source = wheel.m_raycastInfo.m_hardPointWS;
    wheel.m_raycastInfo.m_contactPointWS = source + rayvector;
    const btVector3& target = wheel.m_raycastInfo.m_contactPointWS;

    btScalar param = btScalar(0.);
    
    btVehicleRaycaster::btVehicleRaycasterResult    rayResults;

    btAssert(m_vehicleRaycaster);

    void* object = m_vehicleRaycaster->castRay(source,target,rayResults);

    wheel.m_raycastInfo.m_groundObject = 0;

    if (object)
    {
        param = rayResults.m_distFraction;
        depth = raylen * rayResults.m_distFraction;
        wheel.m_raycastInfo.m_contactNormalWS  = rayResults.m_hitNormalInWorld;
        wheel.m_raycastInfo.m_isInContact = true;
        
        wheel.m_raycastInfo.m_groundObject = &getFixedBody();
        //wheel.m_raycastInfo.m_groundObject = object;


        btScalar hitDistance = param*raylen;
        wheel.m_raycastInfo.m_suspensionLength = hitDistance - wheel.m_wheelsRadius;
        //clamp on max suspension travel

        btScalar  minSuspensionLength = wheel.getSuspensionRestLength() - wheel.m_maxSuspensionTravelCm*btScalar(0.01);
        btScalar maxSuspensionLength = wheel.getSuspensionRestLength()+ wheel.m_maxSuspensionTravelCm*btScalar(0.01);
        if (wheel.m_raycastInfo.m_suspensionLength < minSuspensionLength)
        {
            wheel.m_raycastInfo.m_suspensionLength = minSuspensionLength;
        }
        if (wheel.m_raycastInfo.m_suspensionLength > maxSuspensionLength)
        {
            wheel.m_raycastInfo.m_suspensionLength = maxSuspensionLength;
        }

        wheel.m_raycastInfo.m_contactPointWS = rayResults.m_hitPointInWorld;

        btScalar denominator= wheel.m_raycastInfo.m_contactNormalWS.dot( wheel.m_raycastInfo.m_wheelDirectionWS );

        btVector3 chassis_velocity_at_contactPoint;
        btVector3 relpos = wheel.m_raycastInfo.m_contactPointWS-getRigidBody()->getCenterOfMassPosition();

        chassis_velocity_at_contactPoint = getRigidBody()->getVelocityInLocalPoint(relpos);

        btScalar projVel = wheel.m_raycastInfo.m_contactNormalWS.dot( chassis_velocity_at_contactPoint );

        if ( denominator >= btScalar(-0.1))
        {
            wheel.m_suspensionRelativeVelocity = btScalar(0.0);
            wheel.m_clippedInvContactDotSuspension = btScalar(1.0) / btScalar(0.1);
        }
        else
        {
            btScalar inv = btScalar(-1.) / denominator;
            wheel.m_suspensionRelativeVelocity = projVel * inv;
            wheel.m_clippedInvContactDotSuspension = inv;
        }
            
    } else
    {
        //put wheel info as in rest position
        wheel.m_raycastInfo.m_suspensionLength = wheel.getSuspensionRestLength();
        wheel.m_suspensionRelativeVelocity = btScalar(0.0);
        wheel.m_raycastInfo.m_contactNormalWS = - wheel.m_raycastInfo.m_wheelDirectionWS;
        wheel.m_clippedInvContactDotSuspension = btScalar(1.0);
    }

    return depth;
}


const btTransform& btRaycastVehicle::getChassisWorldTransform() const
{
    /*if (getRigidBody()->getMotionState())
    {
        btTransform chassisWorldTrans;
        getRigidBody()->getMotionState()->getWorldTransform(chassisWorldTrans);
        return chassisWorldTrans;
    }
    */

    
    return getRigidBody()->getCenterOfMassTransform();
}


void btRaycastVehicle::updateVehicle( btScalar step )
{
    {
        for (int i=0;i<getNumWheels();i++)
        {
            updateWheelTransform(i,false);
        }
    }


    m_currentVehicleSpeedKmHour = btScalar(3.6) * getRigidBody()->getLinearVelocity().length();
    
    const btTransform& chassisTrans = getChassisWorldTransform();

    btVector3 forwardW (
        chassisTrans.getBasis()[0][m_indexForwardAxis],
        chassisTrans.getBasis()[1][m_indexForwardAxis],
        chassisTrans.getBasis()[2][m_indexForwardAxis]);

    if (forwardW.dot(getRigidBody()->getLinearVelocity()) < btScalar(0.))
    {
        m_currentVehicleSpeedKmHour *= btScalar(-1.);
    }

    //
    // simulate suspension
    //
    
    int i=0;
    for (i=0;i<m_wheelInfo.size();i++)
    {
        btScalar depth; 
        depth = rayCast( m_wheelInfo[i]);
    }

    updateSuspension(step);

    
    for (i=0;i<m_wheelInfo.size();i++)
    {
        //apply suspension force
        btWheelInfo& wheel = m_wheelInfo[i];
        
        btScalar suspensionForce = wheel.m_wheelsSuspensionForce;
        
        if (suspensionForce > wheel.m_maxSuspensionForce)
        {
            suspensionForce = wheel.m_maxSuspensionForce;
        }
        btVector3 impulse = wheel.m_raycastInfo.m_contactNormalWS * suspensionForce * step;
        btVector3 relpos = wheel.m_raycastInfo.m_contactPointWS - getRigidBody()->getCenterOfMassPosition();
        
        getRigidBody()->applyImpulse(impulse, relpos);
    
    }
    

    
    updateFriction( step);

    
    for (i=0;i<m_wheelInfo.size();i++)
    {
        btWheelInfo& wheel = m_wheelInfo[i];
        btVector3 relpos = wheel.m_raycastInfo.m_hardPointWS - getRigidBody()->getCenterOfMassPosition();
        btVector3 vel = getRigidBody()->getVelocityInLocalPoint( relpos );

        if (wheel.m_raycastInfo.m_isInContact)
        {
            const btTransform&  chassisWorldTransform = getChassisWorldTransform();

            btVector3 fwd (
                chassisWorldTransform.getBasis()[0][m_indexForwardAxis],
                chassisWorldTransform.getBasis()[1][m_indexForwardAxis],
                chassisWorldTransform.getBasis()[2][m_indexForwardAxis]);

            btScalar proj = fwd.dot(wheel.m_raycastInfo.m_contactNormalWS);
            fwd -= wheel.m_raycastInfo.m_contactNormalWS * proj;

            btScalar proj2 = fwd.dot(vel);
            
            wheel.m_deltaRotation = (proj2 * step) / (wheel.m_wheelsRadius);
            wheel.m_rotation += wheel.m_deltaRotation;

        } else
        {
            wheel.m_rotation += wheel.m_deltaRotation;
        }
        
        wheel.m_deltaRotation *= btScalar(0.99);//damping of rotation when not in contact

    }



}


void    btRaycastVehicle::setSteeringValue(btScalar steering,int wheel)
{
    btAssert(wheel>=0 && wheel < getNumWheels());

    btWheelInfo& wheelInfo = getWheelInfo(wheel);
    wheelInfo.m_steering = steering;
}



btScalar    btRaycastVehicle::getSteeringValue(int wheel) const
{
    return getWheelInfo(wheel).m_steering;
}


void    btRaycastVehicle::applyEngineForce(btScalar force, int wheel)
{
    btAssert(wheel>=0 && wheel < getNumWheels());
    btWheelInfo& wheelInfo = getWheelInfo(wheel);
    wheelInfo.m_engineForce = force;
}


const btWheelInfo&  btRaycastVehicle::getWheelInfo(int index) const
{
    btAssert((index >= 0) && (index <   getNumWheels()));
    
    return m_wheelInfo[index];
}

btWheelInfo&    btRaycastVehicle::getWheelInfo(int index) 
{
    btAssert((index >= 0) && (index <   getNumWheels()));
    
    return m_wheelInfo[index];
}

void btRaycastVehicle::setBrake(btScalar brake,int wheelIndex)
{
    btAssert((wheelIndex >= 0) && (wheelIndex <     getNumWheels()));
    getWheelInfo(wheelIndex).m_brake = brake;
}


void    btRaycastVehicle::updateSuspension(btScalar deltaTime)
{
    (void)deltaTime;

    btScalar chassisMass = btScalar(1.) / m_chassisBody->getInvMass();
    
    for (int w_it=0; w_it<getNumWheels(); w_it++)
    {
        btWheelInfo &wheel_info = m_wheelInfo[w_it];
        
        if ( wheel_info.m_raycastInfo.m_isInContact )
        {
            btScalar force;
            //  Spring
            {
                btScalar    susp_length         = wheel_info.getSuspensionRestLength();
                btScalar    current_length = wheel_info.m_raycastInfo.m_suspensionLength;

                btScalar length_diff = (susp_length - current_length);

                force = wheel_info.m_suspensionStiffness
                    * length_diff * wheel_info.m_clippedInvContactDotSuspension;
            }
        
            // Damper
            {
                btScalar projected_rel_vel = wheel_info.m_suspensionRelativeVelocity;
                {
                    btScalar    susp_damping;
                    if ( projected_rel_vel < btScalar(0.0) )
                    {
                        susp_damping = wheel_info.m_wheelsDampingCompression;
                    }
                    else
                    {
                        susp_damping = wheel_info.m_wheelsDampingRelaxation;
                    }
                    force -= susp_damping * projected_rel_vel;
                }
            }

            // RESULT
            wheel_info.m_wheelsSuspensionForce = force * chassisMass;
            if (wheel_info.m_wheelsSuspensionForce < btScalar(0.))
            {
                wheel_info.m_wheelsSuspensionForce = btScalar(0.);
            }
        }
        else
        {
            wheel_info.m_wheelsSuspensionForce = btScalar(0.0);
        }
    }

}


struct btWheelContactPoint
{
    btRigidBody* m_body0;
    btRigidBody* m_body1;
    btVector3   m_frictionPositionWorld;
    btVector3   m_frictionDirectionWorld;
    btScalar    m_jacDiagABInv;
    btScalar    m_maxImpulse;


    btWheelContactPoint(btRigidBody* body0,btRigidBody* body1,const btVector3& frictionPosWorld,const btVector3& frictionDirectionWorld, btScalar maxImpulse)
        :m_body0(body0),
        m_body1(body1),
        m_frictionPositionWorld(frictionPosWorld),
        m_frictionDirectionWorld(frictionDirectionWorld),
        m_maxImpulse(maxImpulse)
    {
        btScalar denom0 = body0->computeImpulseDenominator(frictionPosWorld,frictionDirectionWorld);
        btScalar denom1 = body1->computeImpulseDenominator(frictionPosWorld,frictionDirectionWorld);
        btScalar    relaxation = 1.f;
        m_jacDiagABInv = relaxation/(denom0+denom1);
    }



};

btScalar calcRollingFriction(btWheelContactPoint& contactPoint);
btScalar calcRollingFriction(btWheelContactPoint& contactPoint)
{

    btScalar j1=0.f;

    const btVector3& contactPosWorld = contactPoint.m_frictionPositionWorld;

    btVector3 rel_pos1 = contactPosWorld - contactPoint.m_body0->getCenterOfMassPosition(); 
    btVector3 rel_pos2 = contactPosWorld - contactPoint.m_body1->getCenterOfMassPosition();
    
    btScalar maxImpulse  = contactPoint.m_maxImpulse;
    
    btVector3 vel1 = contactPoint.m_body0->getVelocityInLocalPoint(rel_pos1);
    btVector3 vel2 = contactPoint.m_body1->getVelocityInLocalPoint(rel_pos2);
    btVector3 vel = vel1 - vel2;

    btScalar vrel = contactPoint.m_frictionDirectionWorld.dot(vel);

    // calculate j that moves us to zero relative velocity
    j1 = -vrel * contactPoint.m_jacDiagABInv;
    btSetMin(j1, maxImpulse);
    btSetMax(j1, -maxImpulse);

    return j1;
}




btScalar sideFrictionStiffness2 = btScalar(1.0);
void    btRaycastVehicle::updateFriction(btScalar   timeStep)
{

        //calculate the impulse, so that the wheels don't move sidewards
        int numWheel = getNumWheels();
        if (!numWheel)
            return;

        m_forwardWS.resize(numWheel);
        m_axle.resize(numWheel);
        m_forwardImpulse.resize(numWheel);
        m_sideImpulse.resize(numWheel);
        
        int numWheelsOnGround = 0;
    

        //collapse all those loops into one!
        for (int i=0;i<getNumWheels();i++)
        {
            btWheelInfo& wheelInfo = m_wheelInfo[i];
            class btRigidBody* groundObject = (class btRigidBody*) wheelInfo.m_raycastInfo.m_groundObject;
            if (groundObject)
                numWheelsOnGround++;
            m_sideImpulse[i] = btScalar(0.);
            m_forwardImpulse[i] = btScalar(0.);

        }
    
        {
    
            for (int i=0;i<getNumWheels();i++)
            {

                btWheelInfo& wheelInfo = m_wheelInfo[i];
                    
                class btRigidBody* groundObject = (class btRigidBody*) wheelInfo.m_raycastInfo.m_groundObject;

                if (groundObject)
                {

                    const btTransform& wheelTrans = getWheelTransformWS( i );

                    btMatrix3x3 wheelBasis0 = wheelTrans.getBasis();
                    m_axle[i] = btVector3(  
                        wheelBasis0[0][m_indexRightAxis],
                        wheelBasis0[1][m_indexRightAxis],
                        wheelBasis0[2][m_indexRightAxis]);
                    
                    const btVector3& surfNormalWS = wheelInfo.m_raycastInfo.m_contactNormalWS;
                    btScalar proj = m_axle[i].dot(surfNormalWS);
                    m_axle[i] -= surfNormalWS * proj;
                    m_axle[i] = m_axle[i].normalize();
                    
                    m_forwardWS[i] = surfNormalWS.cross(m_axle[i]);
                    m_forwardWS[i].normalize();

                
                    resolveSingleBilateral(*m_chassisBody, wheelInfo.m_raycastInfo.m_contactPointWS,
                              *groundObject, wheelInfo.m_raycastInfo.m_contactPointWS,
                              btScalar(0.), m_axle[i],m_sideImpulse[i],timeStep);

                    m_sideImpulse[i] *= sideFrictionStiffness2;
                        
                }
                

            }
        }

    btScalar sideFactor = btScalar(1.);
    btScalar fwdFactor = 0.5;

    bool sliding = false;
    {
        for (int wheel =0;wheel <getNumWheels();wheel++)
        {
            btWheelInfo& wheelInfo = m_wheelInfo[wheel];
            class btRigidBody* groundObject = (class btRigidBody*) wheelInfo.m_raycastInfo.m_groundObject;

            btScalar    rollingFriction = 0.f;

            if (groundObject)
            {
                if (wheelInfo.m_engineForce != 0.f)
                {
                    rollingFriction = wheelInfo.m_engineForce* timeStep;
                } else
                {
                    btScalar defaultRollingFrictionImpulse = 0.f;
                    btScalar maxImpulse = wheelInfo.m_brake ? wheelInfo.m_brake : defaultRollingFrictionImpulse;
                    btWheelContactPoint contactPt(m_chassisBody,groundObject,wheelInfo.m_raycastInfo.m_contactPointWS,m_forwardWS[wheel],maxImpulse);
                    rollingFriction = calcRollingFriction(contactPt);
                }
            }

            //switch between active rolling (throttle), braking and non-active rolling friction (no throttle/break)
            



            m_forwardImpulse[wheel] = btScalar(0.);
            m_wheelInfo[wheel].m_skidInfo= btScalar(1.);

            if (groundObject)
            {
                m_wheelInfo[wheel].m_skidInfo= btScalar(1.);
                
                btScalar maximp = wheelInfo.m_wheelsSuspensionForce * timeStep * wheelInfo.m_frictionSlip;
                btScalar maximpSide = maximp;

                btScalar maximpSquared = maximp * maximpSide;
            

                m_forwardImpulse[wheel] = rollingFriction;//wheelInfo.m_engineForce* timeStep;

                btScalar x = (m_forwardImpulse[wheel] ) * fwdFactor;
                btScalar y = (m_sideImpulse[wheel] ) * sideFactor;
                
                btScalar impulseSquared = (x*x + y*y);

                if (impulseSquared > maximpSquared)
                {
                    sliding = true;
                    
                    btScalar factor = maximp / btSqrt(impulseSquared);
                    
                    m_wheelInfo[wheel].m_skidInfo *= factor;
                }
            } 

        }
    }

    


        if (sliding)
        {
            for (int wheel = 0;wheel < getNumWheels(); wheel++)
            {
                if (m_sideImpulse[wheel] != btScalar(0.))
                {
                    if (m_wheelInfo[wheel].m_skidInfo< btScalar(1.))
                    {
                        m_forwardImpulse[wheel] *=  m_wheelInfo[wheel].m_skidInfo;
                        m_sideImpulse[wheel] *= m_wheelInfo[wheel].m_skidInfo;
                    }
                }
            }
        }

        // apply the impulses
        {
            for (int wheel = 0;wheel<getNumWheels() ; wheel++)
            {
                btWheelInfo& wheelInfo = m_wheelInfo[wheel];

                btVector3 rel_pos = wheelInfo.m_raycastInfo.m_contactPointWS - 
                        m_chassisBody->getCenterOfMassPosition();

                if (m_forwardImpulse[wheel] != btScalar(0.))
                {
                    m_chassisBody->applyImpulse(m_forwardWS[wheel]*(m_forwardImpulse[wheel]),rel_pos);
                }
                if (m_sideImpulse[wheel] != btScalar(0.))
                {
                    class btRigidBody* groundObject = (class btRigidBody*) m_wheelInfo[wheel].m_raycastInfo.m_groundObject;

                    btVector3 rel_pos2 = wheelInfo.m_raycastInfo.m_contactPointWS - 
                        groundObject->getCenterOfMassPosition();

                    
                    btVector3 sideImp = m_axle[wheel] * m_sideImpulse[wheel];

#if defined ROLLING_INFLUENCE_FIX // fix. It only worked if car's up was along Y - VT.
                    btVector3 vChassisWorldUp = getRigidBody()->getCenterOfMassTransform().getBasis().getColumn(m_indexUpAxis);
                    rel_pos -= vChassisWorldUp * (vChassisWorldUp.dot(rel_pos) * (1.f-wheelInfo.m_rollInfluence));
#else
                    rel_pos[m_indexUpAxis] *= wheelInfo.m_rollInfluence;
#endif
                    m_chassisBody->applyImpulse(sideImp,rel_pos);

                    //apply friction impulse on the ground
                    groundObject->applyImpulse(-sideImp,rel_pos2);
                }
            }
        }

    
}



void    btRaycastVehicle::debugDraw(btIDebugDraw* debugDrawer)
{

    for (int v=0;v<this->getNumWheels();v++)
    {
        btVector3 wheelColor(0,1,1);
        if (getWheelInfo(v).m_raycastInfo.m_isInContact)
        {
            wheelColor.setValue(0,0,1);
        } else
        {
            wheelColor.setValue(1,0,1);
        }

        btVector3 wheelPosWS = getWheelInfo(v).m_worldTransform.getOrigin();

        btVector3 axle = btVector3( 
            getWheelInfo(v).m_worldTransform.getBasis()[0][getRightAxis()],
            getWheelInfo(v).m_worldTransform.getBasis()[1][getRightAxis()],
            getWheelInfo(v).m_worldTransform.getBasis()[2][getRightAxis()]);

        //debug wheels (cylinders)
        debugDrawer->drawLine(wheelPosWS,wheelPosWS+axle,wheelColor);
        debugDrawer->drawLine(wheelPosWS,getWheelInfo(v).m_raycastInfo.m_contactPointWS,wheelColor);

    }
}


void* btDefaultVehicleRaycaster::castRay(const btVector3& from,const btVector3& to, btVehicleRaycasterResult& result)
{
//  RayResultCallback& resultCallback;

    btCollisionWorld::ClosestRayResultCallback rayCallback(from,to);

    m_dynamicsWorld->rayTest(from, to, rayCallback);

    if (rayCallback.hasHit())
    {
        
        btRigidBody* body = btRigidBody::upcast(rayCallback.m_collisionObject);
        if (body && body->hasContactResponse())
        {
            result.m_hitPointInWorld = rayCallback.m_hitPointWorld;
            result.m_hitNormalInWorld = rayCallback.m_hitNormalWorld;
            result.m_hitNormalInWorld.normalize();
            result.m_distFraction = rayCallback.m_closestHitFraction;
            return body;
        }
    }
    return 0;
}