text: /*
  * Copyright (c) 2006-2007 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_DISTANCE_JOINT_H
  #define B2_DISTANCE_JOINT_H
  
  #include <Box2D/Dynamics/Joints/b2Joint.h>
  
  /// Distance joint definition. This requires defining an
  /// anchor point on both bodies and the non-zero length of the
  /// distance joint. The definition uses local anchor points
  /// so that the initial configuration can violate the constraint
  /// slightly. This helps when saving and loading a game.
  /// @warning Do not use a zero or short length.
  struct b2DistanceJointDef : public b2JointDef
  {
  	b2DistanceJointDef()
  	{
  		type = e_distanceJoint;
  		localAnchorA.Set(0.0f, 0.0f);
  		localAnchorB.Set(0.0f, 0.0f);
  		length = 1.0f;
  		frequencyHz = 0.0f;
  		dampingRatio = 0.0f;
  	}
  
  	/// Initialize the bodies, anchors, and length using the world
  	/// anchors.
  	void Initialize(b2Body* bodyA, b2Body* bodyB,
  					const b2Vec2& anchorA, const b2Vec2& anchorB);
  
  	/// The local anchor point relative to body1's origin.
  	b2Vec2 localAnchorA;
  
  	/// The local anchor point relative to body2's origin.
  	b2Vec2 localAnchorB;
  
  	/// The natural length between the anchor points.
  	float32 length;
  
  	/// The mass-spring-damper frequency in Hertz.
  	float32 frequencyHz;
  
  	/// The damping ratio. 0 = no damping, 1 = critical damping.
  	float32 dampingRatio;
  };
  
  /// A distance joint constrains two points on two bodies
  /// to remain at a fixed distance from each other. You can view
  /// this as a massless, rigid rod.
  class b2DistanceJoint : public b2Joint
  {
  public:
  
  	b2Vec2 GetAnchorA() const;
  	b2Vec2 GetAnchorB() const;
  
  	/// Get the reaction force given the inverse time step.
  	/// Unit is N.
  	b2Vec2 GetReactionForce(float32 inv_dt) const;
  
  	/// Get the reaction torque given the inverse time step.
  	/// Unit is N*m. This is always zero for a distance joint.
  	float32 GetReactionTorque(float32 inv_dt) const;
  
  	/// Set/get the natural length.
  	/// Manipulating the length can lead to non-physical behavior when the frequency is zero.
  	void SetLength(float32 length);
  	float32 GetLength() const;
  
  	// Set/get frequency in Hz.
  	void SetFrequency(float32 hz);
  	float32 GetFrequency() const;
  
  	// Set/get damping ratio.
  	void SetDampingRatio(float32 ratio);
  	float32 GetDampingRatio() const;
  
  protected:
  
  	friend class b2Joint;
  	b2DistanceJoint(const b2DistanceJointDef* data);
  
  	void InitVelocityConstraints(const b2SolverData& data);
  	void SolveVelocityConstraints(const b2SolverData& data);
  	bool SolvePositionConstraints(const b2SolverData& data);
  
  	float32 m_frequencyHz;
  	float32 m_dampingRatio;
  	float32 m_bias;
  
  	// Solver shared
  	b2Vec2 m_localAnchorA;
  	b2Vec2 m_localAnchorB;
  	float32 m_gamma;
  	float32 m_impulse;
  	float32 m_length;
  
  	// Solver temp
  	int32 m_indexA;
  	int32 m_indexB;
  	b2Vec2 m_u;
  	b2Vec2 m_rA;
  	b2Vec2 m_rB;
  	b2Vec2 m_localCenterA;
  	b2Vec2 m_localCenterB;
  	float32 m_invMassA;
  	float32 m_invMassB;
  	float32 m_invIA;
  	float32 m_invIB;
  	float32 m_mass;
  };
  
  inline void b2DistanceJoint::SetLength(float32 length)
  {
  	m_length = length;
  }
  
  inline float32 b2DistanceJoint::GetLength() const
  {
  	return m_length;
  }
  
  inline void b2DistanceJoint::SetFrequency(float32 hz)
  {
  	m_frequencyHz = hz;
  }
  
  inline float32 b2DistanceJoint::GetFrequency() const
  {
  	return m_frequencyHz;
  }
  
  inline void b2DistanceJoint::SetDampingRatio(float32 ratio)
  {
  	m_dampingRatio = ratio;
  }
  
  inline float32 b2DistanceJoint::GetDampingRatio() const
  {
  	return m_dampingRatio;
  }
  
  #endif
  