godot/scene/3d/vehicle_body.cpp

/*************************************************************************/
/*  vehicle_body.cpp                                                     */
/*************************************************************************/
/*                       This file is part of:                           */
/*                           GODOT ENGINE                                */
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/* Copyright (c) 2007-2016 Juan Linietsky, Ariel Manzur.                 */
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#include "vehicle_body.h"

#define ROLLING_INFLUENCE_FIX

class btVehicleJacobianEntry
{
public:

	Vector3	m_linearJointAxis;
	Vector3	m_aJ;
	Vector3	m_bJ;
	Vector3	m_0MinvJt;
	Vector3	m_1MinvJt;
	//Optimization: can be stored in the w/last component of one of the vectors
	real_t	m_Adiag;

	real_t getDiagonal() const { return m_Adiag; }

	btVehicleJacobianEntry() {};
		//constraint between two different rigidbodies
		btVehicleJacobianEntry(
			const Matrix3& world2A,
			const Matrix3& world2B,
			const Vector3& rel_pos1,
			const Vector3& rel_pos2,
			const Vector3& jointAxis,
			const Vector3& inertiaInvA,
			const real_t massInvA,
			const Vector3& inertiaInvB,
			const real_t massInvB)
			:m_linearJointAxis(jointAxis)
		{
			m_aJ = world2A.xform(rel_pos1.cross(m_linearJointAxis));
			m_bJ = world2B.xform(rel_pos2.cross(-m_linearJointAxis));
			m_0MinvJt	= inertiaInvA * m_aJ;
			m_1MinvJt = inertiaInvB * m_bJ;
			m_Adiag = massInvA + m_0MinvJt.dot(m_aJ) + massInvB + m_1MinvJt.dot(m_bJ);

			//btAssert(m_Adiag > real_t(0.0));
		}

		real_t getRelativeVelocity(const Vector3& linvelA,const Vector3& angvelA,const Vector3& linvelB,const Vector3& angvelB)
			{
				Vector3 linrel = linvelA - linvelB;
				Vector3 angvela  = angvelA * m_aJ;
				Vector3 angvelb  = angvelB * m_bJ;
				linrel *= m_linearJointAxis;
				angvela += angvelb;
				angvela += linrel;
				real_t rel_vel2 = angvela[0]+angvela[1]+angvela[2];
				return rel_vel2 + CMP_EPSILON;
			}


};

void VehicleWheel::_notification(int p_what) {


	if (p_what==NOTIFICATION_ENTER_TREE) {

		if (!get_parent())
			return;
		VehicleBody *cb = get_parent()->cast_to<VehicleBody>();
		if (!cb)
			return;
		body=cb;
		local_xform=get_transform();
		cb->wheels.push_back(this);

		m_chassisConnectionPointCS = get_transform().origin;
		m_wheelDirectionCS = -get_transform().basis.get_axis(Vector3::AXIS_Y).normalized();
		m_wheelAxleCS = get_transform().basis.get_axis(Vector3::AXIS_X).normalized();

	}
	if (p_what==NOTIFICATION_EXIT_TREE) {

		if (!get_parent())
			return;
		VehicleBody *cb = get_parent()->cast_to<VehicleBody>();
		if (!cb)
			return;
		cb->wheels.erase(this);
		body=NULL;
	}

}


void VehicleWheel::_update(PhysicsDirectBodyState *s) {



	if (m_raycastInfo.m_isInContact)

	{
		real_t	project= m_raycastInfo.m_contactNormalWS.dot( m_raycastInfo.m_wheelDirectionWS );
		Vector3	 chassis_velocity_at_contactPoint;
		Vector3 relpos = m_raycastInfo.m_contactPointWS - s->get_transform().origin;

		chassis_velocity_at_contactPoint = s->get_linear_velocity() +
				(s->get_angular_velocity()).cross(relpos);// * mPos);

		real_t projVel = m_raycastInfo.m_contactNormalWS.dot( chassis_velocity_at_contactPoint );
		if ( project >= real_t(-0.1))
		{
			m_suspensionRelativeVelocity = real_t(0.0);
			m_clippedInvContactDotSuspension = real_t(1.0) / real_t(0.1);
		}
		else
		{
			real_t inv = real_t(-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 = m_suspensionRestLength;
		m_suspensionRelativeVelocity = real_t(0.0);
		m_raycastInfo.m_contactNormalWS = -m_raycastInfo.m_wheelDirectionWS;
		m_clippedInvContactDotSuspension = real_t(1.0);
	}
}

void VehicleWheel::set_radius(float p_radius) {

	m_wheelRadius=p_radius;
	update_gizmo();
}

float VehicleWheel::get_radius() const{

	return m_wheelRadius;
}

void VehicleWheel::set_suspension_rest_length(float p_length){

	m_suspensionRestLength=p_length;
	update_gizmo();
}
float VehicleWheel::get_suspension_rest_length() const{

	return m_suspensionRestLength;
}

void VehicleWheel::set_suspension_travel(float p_length){

	m_maxSuspensionTravelCm=p_length/0.01;
}
float VehicleWheel::get_suspension_travel() const{

	return m_maxSuspensionTravelCm*0.01;
}

void VehicleWheel::set_suspension_stiffness(float p_value){

	m_suspensionStiffness=p_value;
}
float VehicleWheel::get_suspension_stiffness() const{

	return m_suspensionStiffness;
}

void VehicleWheel::set_suspension_max_force(float p_value){

	m_maxSuspensionForce=p_value;
}
float VehicleWheel::get_suspension_max_force() const{

	return m_maxSuspensionForce;
}

void VehicleWheel::set_damping_compression(float p_value){

	m_wheelsDampingCompression=p_value;
}
float VehicleWheel::get_damping_compression() const{

	return m_wheelsDampingCompression;
}

void VehicleWheel::set_damping_relaxation(float p_value){

	m_wheelsDampingRelaxation=p_value;
}
float VehicleWheel::get_damping_relaxation() const{

	return m_wheelsDampingRelaxation;
}

void VehicleWheel::set_friction_slip(float p_value) {

	m_frictionSlip=p_value;
}
float VehicleWheel::get_friction_slip() const{

	return m_frictionSlip;
}


void VehicleWheel::_bind_methods() {


	ObjectTypeDB::bind_method(_MD("set_radius","length"),&VehicleWheel::set_radius);
	ObjectTypeDB::bind_method(_MD("get_radius"),&VehicleWheel::get_radius);

	ObjectTypeDB::bind_method(_MD("set_suspension_rest_length","length"),&VehicleWheel::set_suspension_rest_length);
	ObjectTypeDB::bind_method(_MD("get_suspension_rest_length"),&VehicleWheel::get_suspension_rest_length);

	ObjectTypeDB::bind_method(_MD("set_suspension_travel","length"),&VehicleWheel::set_suspension_travel);
	ObjectTypeDB::bind_method(_MD("get_suspension_travel"),&VehicleWheel::get_suspension_travel);

	ObjectTypeDB::bind_method(_MD("set_suspension_stiffness","length"),&VehicleWheel::set_suspension_stiffness);
	ObjectTypeDB::bind_method(_MD("get_suspension_stiffness"),&VehicleWheel::get_suspension_stiffness);

	ObjectTypeDB::bind_method(_MD("set_suspension_max_force","length"),&VehicleWheel::set_suspension_max_force);
	ObjectTypeDB::bind_method(_MD("get_suspension_max_force"),&VehicleWheel::get_suspension_max_force);


	ObjectTypeDB::bind_method(_MD("set_damping_compression","length"),&VehicleWheel::set_damping_compression);
	ObjectTypeDB::bind_method(_MD("get_damping_compression"),&VehicleWheel::get_damping_compression);

	ObjectTypeDB::bind_method(_MD("set_damping_relaxation","length"),&VehicleWheel::set_damping_relaxation);
	ObjectTypeDB::bind_method(_MD("get_damping_relaxation"),&VehicleWheel::get_damping_relaxation);

	ObjectTypeDB::bind_method(_MD("set_use_as_traction","enable"),&VehicleWheel::set_use_as_traction);
	ObjectTypeDB::bind_method(_MD("is_used_as_traction"),&VehicleWheel::is_used_as_traction);

	ObjectTypeDB::bind_method(_MD("set_use_as_steering","enable"),&VehicleWheel::set_use_as_steering);
	ObjectTypeDB::bind_method(_MD("is_used_as_steering"),&VehicleWheel::is_used_as_steering);

	ObjectTypeDB::bind_method(_MD("set_friction_slip","length"),&VehicleWheel::set_friction_slip);
	ObjectTypeDB::bind_method(_MD("get_friction_slip"),&VehicleWheel::get_friction_slip);


	ADD_PROPERTY(PropertyInfo(Variant::BOOL,"type/traction"),_SCS("set_use_as_traction"),_SCS("is_used_as_traction"));
	ADD_PROPERTY(PropertyInfo(Variant::BOOL,"type/steering"),_SCS("set_use_as_steering"),_SCS("is_used_as_steering"));
	ADD_PROPERTY(PropertyInfo(Variant::REAL,"wheel/radius"),_SCS("set_radius"),_SCS("get_radius"));
	ADD_PROPERTY(PropertyInfo(Variant::REAL,"wheel/rest_length"),_SCS("set_suspension_rest_length"),_SCS("get_suspension_rest_length"));
	ADD_PROPERTY(PropertyInfo(Variant::REAL,"wheel/friction_slip"),_SCS("set_friction_slip"),_SCS("get_friction_slip"));
	ADD_PROPERTY(PropertyInfo(Variant::REAL,"suspension/travel"),_SCS("set_suspension_travel"),_SCS("get_suspension_travel"));
	ADD_PROPERTY(PropertyInfo(Variant::REAL,"suspension/stiffness"),_SCS("set_suspension_stiffness"),_SCS("get_suspension_stiffness"));
	ADD_PROPERTY(PropertyInfo(Variant::REAL,"suspension/max_force"),_SCS("set_suspension_max_force"),_SCS("get_suspension_max_force"));
	ADD_PROPERTY(PropertyInfo(Variant::REAL,"damping/compression"),_SCS("set_damping_compression"),_SCS("get_damping_compression"));
	ADD_PROPERTY(PropertyInfo(Variant::REAL,"damping/relaxation"),_SCS("set_damping_relaxation"),_SCS("get_damping_relaxation"));

}


void VehicleWheel::set_use_as_traction(bool p_enable) {

	engine_traction=p_enable;
}

bool VehicleWheel::is_used_as_traction() const{

	return engine_traction;
}


void VehicleWheel::set_use_as_steering(bool p_enabled){

	steers=p_enabled;
}

bool VehicleWheel::is_used_as_steering() const{

	return steers;
}


VehicleWheel::VehicleWheel() {


	steers=false;
	engine_traction=false;

	m_steering = real_t(0.);
	//m_engineForce = real_t(0.);
	m_rotation = real_t(0.);
	m_deltaRotation = real_t(0.);
	m_brake = real_t(0.);
	m_rollInfluence = real_t(0.1);

	m_suspensionRestLength = 0.15;
	m_wheelRadius = 0.5;//0.28;
	m_suspensionStiffness = 5.88;
	m_wheelsDampingCompression = 0.83;
	m_wheelsDampingRelaxation = 0.88;
	m_frictionSlip = 10.5;
	m_bIsFrontWheel = false;
	m_maxSuspensionTravelCm = 500;
	m_maxSuspensionForce = 6000;

	m_suspensionRelativeVelocity=0;
	m_clippedInvContactDotSuspension=1.0;
	m_raycastInfo.m_isInContact=false;

	body=NULL;
}


void VehicleBody::_update_wheel_transform(VehicleWheel& wheel ,PhysicsDirectBodyState *s) {

	wheel.m_raycastInfo.m_isInContact = false;

	Transform chassisTrans = s->get_transform();
	//if (interpolatedTransform && (getRigidBody()->getMotionState()))
	//{
	//	getRigidBody()->getMotionState()->getWorldTransform(chassisTrans);
	//}

	wheel.m_raycastInfo.m_hardPointWS = chassisTrans.xform( wheel.m_chassisConnectionPointCS );
	//wheel.m_raycastInfo.m_hardPointWS+=s->get_linear_velocity()*s->get_step();
	wheel.m_raycastInfo.m_wheelDirectionWS = chassisTrans.get_basis().xform( wheel.m_wheelDirectionCS).normalized();
	wheel.m_raycastInfo.m_wheelAxleWS = chassisTrans.get_basis().xform( wheel.m_wheelAxleCS ).normalized();
}

void VehicleBody::_update_wheel(int p_idx,PhysicsDirectBodyState *s) {

	VehicleWheel& wheel = *wheels[p_idx];
	_update_wheel_transform(wheel,s);

	Vector3 up = -wheel.m_raycastInfo.m_wheelDirectionWS;
	const Vector3& right = wheel.m_raycastInfo.m_wheelAxleWS;
	Vector3 fwd = up.cross(right);
	fwd = fwd.normalized();
//	up = right.cross(fwd);
//	up.normalize();

	//rotate around steering over de wheelAxleWS
	real_t steering = wheel.steers?m_steeringValue:0.0;
	//print_line(itos(p_idx)+": "+rtos(steering));

	Matrix3 steeringMat(up,steering);

	Matrix3 rotatingMat(right,-wheel.m_rotation);

//	if (p_idx==1)
//		print_line("steeringMat " +steeringMat);

	Matrix3 basis2(
		right[0],up[0],fwd[0],
		right[1],up[1],fwd[1],
		right[2],up[2],fwd[2]
	);

	wheel.m_worldTransform.set_basis(steeringMat * rotatingMat * basis2);
	//wheel.m_worldTransform.set_basis(basis2 * (steeringMat * rotatingMat));
	wheel.m_worldTransform.set_origin(
		wheel.m_raycastInfo.m_hardPointWS + wheel.m_raycastInfo.m_wheelDirectionWS * wheel.m_raycastInfo.m_suspensionLength
	);

}


real_t VehicleBody::_ray_cast(int p_idx,PhysicsDirectBodyState *s) {


	VehicleWheel& wheel = *wheels[p_idx];

	_update_wheel_transform(wheel,s);


	real_t depth = -1;

	real_t raylen = wheel.m_suspensionRestLength+wheel.m_wheelRadius;

	Vector3 rayvector = wheel.m_raycastInfo.m_wheelDirectionWS * (raylen);
	Vector3 source = wheel.m_raycastInfo.m_hardPointWS;
	wheel.m_raycastInfo.m_contactPointWS = source + rayvector;
	const Vector3& target = wheel.m_raycastInfo.m_contactPointWS;
	source-=wheel.m_wheelRadius * wheel.m_raycastInfo.m_wheelDirectionWS;

	real_t param = real_t(0.);


	PhysicsDirectSpaceState::RayResult rr;


	PhysicsDirectSpaceState *ss=s->get_space_state();

	bool col = ss->intersect_ray(source,target,rr,exclude);


	wheel.m_raycastInfo.m_groundObject = 0;

	if (col)
	{
		//print_line("WHEEL "+itos(p_idx)+" FROM "+source+" TO: "+target);
		//print_line("WHEEL "+itos(p_idx)+" COLLIDE? "+itos(col));
		param = source.distance_to(rr.position)/source.distance_to(target);
		depth = raylen * param;
		wheel.m_raycastInfo.m_contactNormalWS  = rr.normal;

		wheel.m_raycastInfo.m_isInContact = true;
		if (rr.collider)
			wheel.m_raycastInfo.m_groundObject=rr.collider->cast_to<PhysicsBody>();


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

		real_t  minSuspensionLength = wheel.m_suspensionRestLength - wheel.m_maxSuspensionTravelCm*real_t(0.01);
		real_t maxSuspensionLength = wheel.m_suspensionRestLength+ wheel.m_maxSuspensionTravelCm*real_t(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 = rr.position;

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

		Vector3 chassis_velocity_at_contactPoint;
		//Vector3 relpos = wheel.m_raycastInfo.m_contactPointWS-getRigidBody()->getCenterOfMassPosition();

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

		chassis_velocity_at_contactPoint = s->get_linear_velocity() +
				(s->get_angular_velocity()).cross(wheel.m_raycastInfo.m_contactPointWS-s->get_transform().origin);// * mPos);


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

		if ( denominator >= real_t(-0.1))
		{
			wheel.m_suspensionRelativeVelocity = real_t(0.0);
			wheel.m_clippedInvContactDotSuspension = real_t(1.0) / real_t(0.1);
		}
		else
		{
			real_t inv = real_t(-1.) / denominator;
			wheel.m_suspensionRelativeVelocity = projVel * inv;
			wheel.m_clippedInvContactDotSuspension = inv;
		}

	} else
	{
		wheel.m_raycastInfo.m_isInContact = false;
		//put wheel info as in rest position
		wheel.m_raycastInfo.m_suspensionLength = wheel.m_suspensionRestLength;
		wheel.m_suspensionRelativeVelocity = real_t(0.0);
		wheel.m_raycastInfo.m_contactNormalWS = - wheel.m_raycastInfo.m_wheelDirectionWS;
		wheel.m_clippedInvContactDotSuspension = real_t(1.0);
	}

	return depth;
}


void	VehicleBody::_update_suspension(PhysicsDirectBodyState *s)
{

	real_t chassisMass = mass;

	for (int w_it=0; w_it<wheels.size(); w_it++)
	{
		VehicleWheel& wheel_info = *wheels[w_it];


		if ( wheel_info.m_raycastInfo.m_isInContact )
		{
			real_t force;
			//	Spring
			{
				real_t	susp_length			= wheel_info.m_suspensionRestLength;
				real_t	current_length = wheel_info.m_raycastInfo.m_suspensionLength;

				real_t length_diff = (susp_length - current_length);

				force = wheel_info.m_suspensionStiffness
					* length_diff * wheel_info.m_clippedInvContactDotSuspension;
			}

			// Damper
			{
				real_t projected_rel_vel = wheel_info.m_suspensionRelativeVelocity;
				{
					real_t	susp_damping;
					if ( projected_rel_vel < real_t(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 < real_t(0.))
			{
				wheel_info.m_wheelsSuspensionForce = real_t(0.);
			}
		}
		else
		{
			wheel_info.m_wheelsSuspensionForce = real_t(0.0);
		}
	}

}


//bilateral constraint between two dynamic objects
void VehicleBody::_resolve_single_bilateral(PhysicsDirectBodyState *s, const Vector3& pos1,
		      PhysicsBody* body2, const Vector3& pos2, const Vector3& normal,real_t& impulse)
{

	real_t normalLenSqr = normal.length_squared();
	//ERR_FAIL_COND( normalLenSqr < real_t(1.1));

	if (normalLenSqr > real_t(1.1))
	{
		impulse = real_t(0.);
		return;
	}

	Vector3 rel_pos1 = pos1 - s->get_transform().origin;
	Vector3 rel_pos2;
	if (body2)
		rel_pos2 = pos2 - body2->get_global_transform().origin;
	//this jacobian entry could be re-used for all iterations

	Vector3 vel1 = s->get_linear_velocity() +  (s->get_angular_velocity()).cross(rel_pos1);// * mPos);
	Vector3 vel2;

	if (body2)
		vel2=body2->get_linear_velocity() + body2->get_angular_velocity().cross(rel_pos2);

	Vector3 vel = vel1 - vel2;

	Matrix3 b2trans;
	float b2invmass=0;
	Vector3 b2lv;
	Vector3 b2av;
	Vector3 b2invinertia; //todo

	if (body2) {
		b2trans = body2->get_global_transform().basis.transposed();
		b2invmass = body2->get_inverse_mass();
		b2lv = body2->get_linear_velocity();
		b2av = body2->get_angular_velocity();
	}



	btVehicleJacobianEntry jac(s->get_transform().basis.transposed(),
			    b2trans,
			    rel_pos1,
			    rel_pos2,
			    normal,
			    s->get_inverse_inertia(),
			    1.0/mass,
			    b2invinertia,
			    b2invmass);

	real_t rel_vel = jac.getRelativeVelocity(
				s->get_linear_velocity(),
				s->get_transform().basis.transposed().xform(s->get_angular_velocity()),
				b2lv,
				b2trans.xform(b2av));


	rel_vel = normal.dot(vel);

	//TODO: move this into proper structure
	real_t contactDamping = real_t(0.4);
#define ONLY_USE_LINEAR_MASS
#ifdef ONLY_USE_LINEAR_MASS
	real_t massTerm = real_t(1.) / ((1.0/mass) + b2invmass);
	impulse = - contactDamping * rel_vel * massTerm;
#else
	real_t velocityImpulse = -contactDamping * rel_vel * jacDiagABInv;
	impulse = velocityImpulse;
#endif

}



VehicleBody::btVehicleWheelContactPoint::btVehicleWheelContactPoint(PhysicsDirectBodyState *s,PhysicsBody* body1,const Vector3& frictionPosWorld,const Vector3& frictionDirectionWorld, real_t maxImpulse)
	:m_s(s),
	m_body1(body1),
	m_frictionPositionWorld(frictionPosWorld),
	m_frictionDirectionWorld(frictionDirectionWorld),
	m_maxImpulse(maxImpulse)
{
	float denom0=0;
	float denom1=0;

	{
		Vector3 r0 = frictionPosWorld - s->get_transform().origin;
		Vector3 c0 = (r0).cross(frictionDirectionWorld);
		Vector3 vec = s->get_inverse_inertia_tensor().xform_inv(c0).cross(r0);
		denom0= s->get_inverse_mass() + frictionDirectionWorld.dot(vec);
	}

	/* TODO: Why is this code unused?
	if (body1) {

		Vector3 r0 = frictionPosWorld - body1->get_global_transform().origin;
		Vector3 c0 = (r0).cross(frictionDirectionWorld);
		Vector3 vec = s->get_inverse_inertia_tensor().xform_inv(c0).cross(r0);
		//denom1= body1->get_inverse_mass() + frictionDirectionWorld.dot(vec);

	}
	*/

	real_t	relaxation = 1.f;
	m_jacDiagABInv = relaxation/(denom0+denom1);
}


real_t VehicleBody::_calc_rolling_friction(btVehicleWheelContactPoint& contactPoint) {

	real_t j1=0.f;

	const Vector3& contactPosWorld = contactPoint.m_frictionPositionWorld;

	Vector3 rel_pos1 = contactPosWorld - contactPoint.m_s->get_transform().origin;
	Vector3 rel_pos2;
	if (contactPoint.m_body1)
		rel_pos2 = contactPosWorld - contactPoint.m_body1->get_global_transform().origin;

	real_t maxImpulse  = contactPoint.m_maxImpulse;

	Vector3 vel1  = contactPoint.m_s->get_linear_velocity() + (contactPoint.m_s->get_angular_velocity()).cross(rel_pos1);// * mPos);

	Vector3 vel2;
	if (contactPoint.m_body1) {
		vel2=contactPoint.m_body1->get_linear_velocity() + contactPoint.m_body1->get_angular_velocity().cross(rel_pos2);

	}

	Vector3 vel = vel1 - vel2;

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

	// calculate j that moves us to zero relative velocity
	j1 = -vrel * contactPoint.m_jacDiagABInv;

	return CLAMP(j1,-maxImpulse,maxImpulse);
}


static const real_t sideFrictionStiffness2 = real_t(1.0);
void VehicleBody::_update_friction(PhysicsDirectBodyState *s) {

	//calculate the impulse, so that the wheels don't move sidewards
	int numWheel = wheels.size();
	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<wheels.size();i++)
	{
		VehicleWheel& wheelInfo = *wheels[i];
		if (wheelInfo.m_raycastInfo.m_isInContact)
			numWheelsOnGround++;
		m_sideImpulse[i] = real_t(0.);
		m_forwardImpulse[i] = real_t(0.);

	}

	{

		for (int i=0;i<wheels.size();i++)
		{

			VehicleWheel& wheelInfo = *wheels[i];


			if (wheelInfo.m_raycastInfo.m_isInContact)
			{

				//const btTransform& wheelTrans = getWheelTransformWS( i );

				Matrix3 wheelBasis0 = wheelInfo.m_worldTransform.basis;//get_global_transform().basis;

				m_axle[i] = wheelBasis0.get_axis(Vector3::AXIS_X);
				//m_axle[i] = wheelInfo.m_raycastInfo.m_wheelAxleWS;

				const Vector3& surfNormalWS = wheelInfo.m_raycastInfo.m_contactNormalWS;
				real_t proj = m_axle[i].dot(surfNormalWS);
				m_axle[i] -= surfNormalWS * proj;
				m_axle[i] = m_axle[i].normalized();

				m_forwardWS[i] = surfNormalWS.cross(m_axle[i]);
				m_forwardWS[i].normalize();


				_resolve_single_bilateral(s, wheelInfo.m_raycastInfo.m_contactPointWS,
						       wheelInfo.m_raycastInfo.m_groundObject, wheelInfo.m_raycastInfo.m_contactPointWS,
							m_axle[i],m_sideImpulse[i]);

				m_sideImpulse[i] *= sideFrictionStiffness2;


			}
		}
	}

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

	bool sliding = false;
	{
		for (int wheel =0;wheel <wheels.size();wheel++)
		{
			VehicleWheel& wheelInfo = *wheels[wheel];


			//class btRigidBody* groundObject = (class btRigidBody*) wheelInfo.m_raycastInfo.m_groundObject;

			real_t	rollingFriction = 0.f;

			if (wheelInfo.m_raycastInfo.m_isInContact)
			{
				if (engine_force != 0.f)
				{
					rollingFriction = -engine_force* s->get_step();
				} else
				{
					real_t defaultRollingFrictionImpulse = 0.f;
					float cbrake = MAX(wheelInfo.m_brake,brake);
					real_t maxImpulse = cbrake ? cbrake : defaultRollingFrictionImpulse;
					btVehicleWheelContactPoint contactPt(s,wheelInfo.m_raycastInfo.m_groundObject,wheelInfo.m_raycastInfo.m_contactPointWS,m_forwardWS[wheel],maxImpulse);
					rollingFriction = _calc_rolling_friction(contactPt);
				}
			}

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




			m_forwardImpulse[wheel] = real_t(0.);
			wheelInfo.m_skidInfo= real_t(1.);

			if (wheelInfo.m_raycastInfo.m_isInContact)
			{
				wheelInfo.m_skidInfo= real_t(1.);

				real_t maximp = wheelInfo.m_wheelsSuspensionForce * s->get_step() * wheelInfo.m_frictionSlip;
				real_t maximpSide = maximp;

				real_t maximpSquared = maximp * maximpSide;


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

				real_t x = (m_forwardImpulse[wheel] ) * fwdFactor;
				real_t y = (m_sideImpulse[wheel] ) * sideFactor;

				real_t impulseSquared = (x*x + y*y);

				if (impulseSquared > maximpSquared)
				{
					sliding = true;

					real_t factor = maximp / Math::sqrt(impulseSquared);

					wheelInfo.m_skidInfo *= factor;
				}
			}

		}
	}




	if (sliding)
	{
		for (int wheel = 0;wheel < wheels.size(); wheel++)
		{
			if (m_sideImpulse[wheel] != real_t(0.))
			{
				if (wheels[wheel]->m_skidInfo< real_t(1.))
				{
					m_forwardImpulse[wheel] *=	wheels[wheel]->m_skidInfo;
					m_sideImpulse[wheel] *= wheels[wheel]->m_skidInfo;
				}
			}
		}
	}

	// apply the impulses
	{
		for (int wheel = 0;wheel<wheels.size(); wheel++)
		{
			VehicleWheel& wheelInfo = *wheels[wheel];

			Vector3 rel_pos = wheelInfo.m_raycastInfo.m_contactPointWS -
					s->get_transform().origin;

			if (m_forwardImpulse[wheel] != real_t(0.))
			{
				s->apply_impulse(rel_pos,m_forwardWS[wheel]*(m_forwardImpulse[wheel]));
			}
			if (m_sideImpulse[wheel] != real_t(0.))
			{
				PhysicsBody* groundObject = wheelInfo.m_raycastInfo.m_groundObject;

				Vector3 rel_pos2;
				if (groundObject) {
					rel_pos2=wheelInfo.m_raycastInfo.m_contactPointWS - groundObject->get_global_transform().origin;
				}


				Vector3 sideImp = m_axle[wheel] * m_sideImpulse[wheel];

#if defined ROLLING_INFLUENCE_FIX // fix. It only worked if car's up was along Y - VT.
				Vector3 vChassisWorldUp = s->get_transform().basis.transposed()[1];//getRigidBody()->getCenterOfMassTransform().getBasis().getColumn(m_indexUpAxis);
				rel_pos -= vChassisWorldUp * (vChassisWorldUp.dot(rel_pos) * (1.f-wheelInfo.m_rollInfluence));
#else
				rel_pos[1] *= wheelInfo.m_rollInfluence; //?
#endif
				s->apply_impulse(rel_pos,sideImp);

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


}


void VehicleBody::_direct_state_changed(Object *p_state) {


	PhysicsDirectBodyState *s = p_state->cast_to<PhysicsDirectBodyState>();

	set_ignore_transform_notification(true);
	set_global_transform(s->get_transform());
	set_ignore_transform_notification(false);


	float step = s->get_step();

	for(int i=0;i<wheels.size();i++) {

		_update_wheel(i,s);
	}


	for(int i=0;i<wheels.size();i++) {

		_ray_cast(i,s);
		wheels[i]->set_transform(s->get_transform().inverse() * wheels[i]->m_worldTransform);
	}

	_update_suspension(s);

	for(int i=0;i<wheels.size();i++) {

		//apply suspension force
		VehicleWheel& wheel = *wheels[i];

		real_t suspensionForce = wheel.m_wheelsSuspensionForce;

		if (suspensionForce > wheel.m_maxSuspensionForce)
		{
			suspensionForce = wheel.m_maxSuspensionForce;
		}
		Vector3 impulse = wheel.m_raycastInfo.m_contactNormalWS * suspensionForce * step;
		Vector3 relpos = wheel.m_raycastInfo.m_contactPointWS - s->get_transform().origin;

		s->apply_impulse(relpos,impulse);
		//getRigidBody()->applyImpulse(impulse, relpos);

	}


	_update_friction(s);


	for (int i=0;i<wheels.size();i++)
	{
		VehicleWheel& wheel = *wheels[i];
		Vector3 relpos = wheel.m_raycastInfo.m_hardPointWS - s->get_transform().origin;
		Vector3 vel  = s->get_linear_velocity() + (s->get_angular_velocity()).cross(relpos);// * mPos);

		if (wheel.m_raycastInfo.m_isInContact)
		{
			const Transform&	chassisWorldTransform = s->get_transform();

			Vector3 fwd (
				chassisWorldTransform.basis[0][Vector3::AXIS_Z],
				chassisWorldTransform.basis[1][Vector3::AXIS_Z],
				chassisWorldTransform.basis[2][Vector3::AXIS_Z]);

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

			real_t proj2 = fwd.dot(vel);

			wheel.m_deltaRotation = (proj2 * step) / (wheel.m_wheelRadius);
			wheel.m_rotation += wheel.m_deltaRotation;

		} else
		{
			wheel.m_rotation += wheel.m_deltaRotation;
		}

		wheel.m_deltaRotation *= real_t(0.99);//damping of rotation when not in contact

	}
	linear_velocity = s->get_linear_velocity();
}

void VehicleBody::set_mass(real_t p_mass) {

	mass=p_mass;
	PhysicsServer::get_singleton()->body_set_param(get_rid(),PhysicsServer::BODY_PARAM_MASS,mass);
}

real_t VehicleBody::get_mass() const{

	return mass;
}


void VehicleBody::set_friction(real_t p_friction) {

	friction=p_friction;
	PhysicsServer::get_singleton()->body_set_param(get_rid(),PhysicsServer::BODY_PARAM_FRICTION,friction);
}

real_t VehicleBody::get_friction() const{

	return friction;
}

void VehicleBody::set_engine_force(float p_force) {

	engine_force=p_force;
}

float VehicleBody::get_engine_force() const{

	return engine_force;
}

void VehicleBody::set_brake(float p_brake){

	brake=p_brake;
}
float VehicleBody::get_brake() const{

	return brake;
}

void VehicleBody::set_steering(float p_steering){

	m_steeringValue=p_steering;
}
float VehicleBody::get_steering() const{

	return m_steeringValue;
}

Vector3 VehicleBody::get_linear_velocity() const
{
	return linear_velocity;
}

void VehicleBody::_bind_methods(){

	ObjectTypeDB::bind_method(_MD("set_mass","mass"),&VehicleBody::set_mass);
	ObjectTypeDB::bind_method(_MD("get_mass"),&VehicleBody::get_mass);

	ObjectTypeDB::bind_method(_MD("set_friction","friction"),&VehicleBody::set_friction);
	ObjectTypeDB::bind_method(_MD("get_friction"),&VehicleBody::get_friction);

	ObjectTypeDB::bind_method(_MD("set_engine_force","engine_force"),&VehicleBody::set_engine_force);
	ObjectTypeDB::bind_method(_MD("get_engine_force"),&VehicleBody::get_engine_force);

	ObjectTypeDB::bind_method(_MD("set_brake","brake"),&VehicleBody::set_brake);
	ObjectTypeDB::bind_method(_MD("get_brake"),&VehicleBody::get_brake);

	ObjectTypeDB::bind_method(_MD("set_steering","steering"),&VehicleBody::set_steering);
	ObjectTypeDB::bind_method(_MD("get_steering"),&VehicleBody::get_steering);

	ObjectTypeDB::bind_method(_MD("get_linear_velocity"),&VehicleBody::get_linear_velocity);

	ObjectTypeDB::bind_method(_MD("_direct_state_changed"),&VehicleBody::_direct_state_changed);

	ADD_PROPERTY( PropertyInfo(Variant::REAL,"motion/engine_force",PROPERTY_HINT_RANGE,"0.00,1024.0,0.01"),_SCS("set_engine_force"),_SCS("get_engine_force"));
	ADD_PROPERTY( PropertyInfo(Variant::REAL,"motion/brake",PROPERTY_HINT_RANGE,"0.0,1.0,0.01"),_SCS("set_brake"),_SCS("get_brake"));
	ADD_PROPERTY( PropertyInfo(Variant::REAL,"motion/steering",PROPERTY_HINT_RANGE,"-180,180.0,0.01"),_SCS("set_steering"),_SCS("get_steering"));
	ADD_PROPERTY( PropertyInfo(Variant::REAL,"body/mass",PROPERTY_HINT_RANGE,"0.01,65536,0.01"),_SCS("set_mass"),_SCS("get_mass"));
	ADD_PROPERTY( PropertyInfo(Variant::REAL,"body/friction",PROPERTY_HINT_RANGE,"0.01,1,0.01"),_SCS("set_friction"),_SCS("get_friction"));


}



VehicleBody::VehicleBody() : PhysicsBody(PhysicsServer::BODY_MODE_RIGID) {


	m_pitchControl=0;
	m_currentVehicleSpeedKmHour = real_t(0.);
	m_steeringValue = real_t(0.);

	engine_force=0;
	brake=0;



	friction=1;

	ccd=false;

	exclude.insert(get_rid());
	PhysicsServer::get_singleton()->body_set_force_integration_callback(get_rid(),this,"_direct_state_changed");

	set_mass(40);
}