text: /*
  * Copyright (c) 2006-2011 Erin Catto http://www.box2d.org
  *
  * 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.
  */
  
  #ifndef B2_WHEEL_JOINT_H
  #define B2_WHEEL_JOINT_H
  
  #include "../../../Box2D/Dynamics/Joints/b2Joint.h"
  
  /// Wheel joint definition. This requires defining a line of
  /// motion using an axis and an anchor point. The definition uses local
  /// anchor points and a local axis so that the initial configuration
  /// can violate the constraint slightly. The joint translation is zero
  /// when the local anchor points coincide in world space. Using local
  /// anchors and a local axis helps when saving and loading a game.
  struct b2WheelJointDef : public b2JointDef
  {
  	b2WheelJointDef()
  	{
  		type = e_wheelJoint;
  		localAnchorA.SetZero();
  		localAnchorB.SetZero();
  		localAxisA.Set(1.0f, 0.0f);
  		enableMotor = false;
  		maxMotorTorque = 0.0f;
  		motorSpeed = 0.0f;
  		frequencyHz = 2.0f;
  		dampingRatio = 0.7f;
  	}
  
  	/// Initialize the bodies, anchors, axis, and reference angle using the world
  	/// anchor and world axis.
  	void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchor, const b2Vec2& axis);
  
  	/// The local anchor point relative to bodyA's origin.
  	b2Vec2 localAnchorA;
  
  	/// The local anchor point relative to bodyB's origin.
  	b2Vec2 localAnchorB;
  
  	/// The local translation axis in bodyA.
  	b2Vec2 localAxisA;
  
  	/// Enable/disable the joint motor.
  	bool enableMotor;
  
  	/// The maximum motor torque, usually in N-m.
  	float32 maxMotorTorque;
  
  	/// The desired motor speed in radians per second.
  	float32 motorSpeed;
  
  	/// Suspension frequency, zero indicates no suspension
  	float32 frequencyHz;
  
  	/// Suspension damping ratio, one indicates critical damping
  	float32 dampingRatio;
  };
  
  /// A wheel joint. This joint provides two degrees of freedom: translation
  /// along an axis fixed in bodyA and rotation in the plane. You can use a
  /// joint limit to restrict the range of motion and a joint motor to drive
  /// the rotation or to model rotational friction.
  /// This joint is designed for vehicle suspensions.
  class b2WheelJoint : public b2Joint
  {
  public:
  	b2Vec2 GetAnchorA() const;
  	b2Vec2 GetAnchorB() const;
  
  	b2Vec2 GetReactionForce(float32 inv_dt) const;
  	float32 GetReactionTorque(float32 inv_dt) const;
  
  	/// The local anchor point relative to bodyA's origin.
  	const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }
  
  	/// The local anchor point relative to bodyB's origin.
  	const b2Vec2& GetLocalAnchorB() const  { return m_localAnchorB; }
  
  	/// The local joint axis relative to bodyA.
  	const b2Vec2& GetLocalAxisA() const { return m_localXAxisA; }
  
  	/// Get the current joint translation, usually in meters.
  	float32 GetJointTranslation() const;
  
  	/// Get the current joint translation speed, usually in meters per second.
  	float32 GetJointSpeed() const;
  
  	/// Is the joint motor enabled?
  	bool IsMotorEnabled() const;
  
  	/// Enable/disable the joint motor.
  	void EnableMotor(bool flag);
  
  	/// Set the motor speed, usually in radians per second.
  	void SetMotorSpeed(float32 speed);
  
  	/// Get the motor speed, usually in radians per second.
  	float32 GetMotorSpeed() const;
  
  	/// Set/Get the maximum motor force, usually in N-m.
  	void SetMaxMotorTorque(float32 torque);
  	float32 GetMaxMotorTorque() const;
  
  	/// Get the current motor torque given the inverse time step, usually in N-m.
  	float32 GetMotorTorque(float32 inv_dt) const;
  
  	/// Set/Get the spring frequency in hertz. Setting the frequency to zero disables the spring.
  	void SetSpringFrequencyHz(float32 hz);
  	float32 GetSpringFrequencyHz() const;
  
  	/// Set/Get the spring damping ratio
  	void SetSpringDampingRatio(float32 ratio);
  	float32 GetSpringDampingRatio() const;
  
  	/// Dump to b2Log
  	void Dump();
  
  protected:
  
  	friend class b2Joint;
  	b2WheelJoint(const b2WheelJointDef* def);
  
  	void InitVelocityConstraints(const b2SolverData& data);
  	void SolveVelocityConstraints(const b2SolverData& data);
  	bool SolvePositionConstraints(const b2SolverData& data);
  
  	float32 m_frequencyHz;
  	float32 m_dampingRatio;
  
  	// Solver shared
  	b2Vec2 m_localAnchorA;
  	b2Vec2 m_localAnchorB;
  	b2Vec2 m_localXAxisA;
  	b2Vec2 m_localYAxisA;
  
  	float32 m_impulse;
  	float32 m_motorImpulse;
  	float32 m_springImpulse;
  
  	float32 m_maxMotorTorque;
  	float32 m_motorSpeed;
  	bool m_enableMotor;
  
  	// Solver temp
  	int32 m_indexA;
  	int32 m_indexB;
  	b2Vec2 m_localCenterA;
  	b2Vec2 m_localCenterB;
  	float32 m_invMassA;
  	float32 m_invMassB;
  	float32 m_invIA;
  	float32 m_invIB;
  
  	b2Vec2 m_ax, m_ay;
  	float32 m_sAx, m_sBx;
  	float32 m_sAy, m_sBy;
  
  	float32 m_mass;
  	float32 m_motorMass;
  	float32 m_springMass;
  
  	float32 m_bias;
  	float32 m_gamma;
  };
  
  inline float32 b2WheelJoint::GetMotorSpeed() const
  {
  	return m_motorSpeed;
  }
  
  inline float32 b2WheelJoint::GetMaxMotorTorque() const
  {
  	return m_maxMotorTorque;
  }
  
  inline void b2WheelJoint::SetSpringFrequencyHz(float32 hz)
  {
  	m_frequencyHz = hz;
  }
  
  inline float32 b2WheelJoint::GetSpringFrequencyHz() const
  {
  	return m_frequencyHz;
  }
  
  inline void b2WheelJoint::SetSpringDampingRatio(float32 ratio)
  {
  	m_dampingRatio = ratio;
  }
  
  inline float32 b2WheelJoint::GetSpringDampingRatio() const
  {
  	return m_dampingRatio;
  }
  
  #endif
  