source: code/archive/tutorial4/src/external/bullet/BulletDynamics/Vehicle/btWheelInfo.cpp

/*
 * 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 "btWheelInfo.h"
#include "BulletDynamics/Dynamics/btRigidBody.h" // for pointvelocity


btScalar btWheelInfo::getSuspensionRestLength() const
{

        return m_suspensionRestLength1;

}

void    btWheelInfo::updateWheel(const btRigidBody& chassis,RaycastInfo& raycastInfo)
{
        (void)raycastInfo;

        
        if (m_raycastInfo.m_isInContact)

        {
                btScalar        project= m_raycastInfo.m_contactNormalWS.dot( m_raycastInfo.m_wheelDirectionWS );
                btVector3        chassis_velocity_at_contactPoint;
                btVector3 relpos = m_raycastInfo.m_contactPointWS - chassis.getCenterOfMassPosition();
                chassis_velocity_at_contactPoint = chassis.getVelocityInLocalPoint( relpos );
                btScalar projVel = m_raycastInfo.m_contactNormalWS.dot( chassis_velocity_at_contactPoint );
                if ( project >= btScalar(-0.1))
                {
                        m_suspensionRelativeVelocity = btScalar(0.0);
                        m_clippedInvContactDotSuspension = btScalar(1.0) / btScalar(0.1);
                }
                else
                {
                        btScalar inv = btScalar(-1.) / project;
                        m_suspensionRelativeVelocity = projVel * inv;
                        m_clippedInvContactDotSuspension = inv;
                }
                
        }

        else    // Not in contact : position wheel in a nice (rest length) position
        {
                m_raycastInfo.m_suspensionLength = this->getSuspensionRestLength();
                m_suspensionRelativeVelocity = btScalar(0.0);
                m_raycastInfo.m_contactNormalWS = -m_raycastInfo.m_wheelDirectionWS;
                m_clippedInvContactDotSuspension = btScalar(1.0);
        }
}