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_REVOLUTE_JOINT_H
  #define B2_REVOLUTE_JOINT_H
  
  #include <Box2D/Dynamics/Joints/b2Joint.h>
  
  /// Revolute joint definition. This requires defining an
  /// anchor point where the bodies are joined. The definition
  /// uses local anchor points so that the initial configuration
  /// can violate the constraint slightly. You also need to
  /// specify the initial relative angle for joint limits. This
  /// helps when saving and loading a game.
  /// The local anchor points are measured from the body's origin
  /// rather than the center of mass because:
  /// 1. you might not know where the center of mass will be.
  /// 2. if you add/remove shapes from a body and recompute the mass,
  ///    the joints will be broken.
  struct b2RevoluteJointDef : public b2JointDef
  {
  	b2RevoluteJointDef()
  	{
  		type = e_revoluteJoint;
  		localAnchorA.Set(0.0f, 0.0f);
  		localAnchorB.Set(0.0f, 0.0f);
  		referenceAngle = 0.0f;
  		lowerAngle = 0.0f;
  		upperAngle = 0.0f;
  		maxMotorTorque = 0.0f;
  		motorSpeed = 0.0f;
  		enableLimit = false;
  		enableMotor = false;
  	}
  
  	/// Initialize the bodies, anchors, and reference angle using a world
  	/// anchor point.
  	void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchor);
  
  	/// The local anchor point relative to bodyA's origin.
  	b2Vec2 localAnchorA;
  
  	/// The local anchor point relative to bodyB's origin.
  	b2Vec2 localAnchorB;
  
  	/// The bodyB angle minus bodyA angle in the reference state (radians).
  	float32 referenceAngle;
  
  	/// A flag to enable joint limits.
  	bool enableLimit;
  
  	/// The lower angle for the joint limit (radians).
  	float32 lowerAngle;
  
  	/// The upper angle for the joint limit (radians).
  	float32 upperAngle;
  
  	/// A flag to enable the joint motor.
  	bool enableMotor;
  
  	/// The desired motor speed. Usually in radians per second.
  	float32 motorSpeed;
  
  	/// The maximum motor torque used to achieve the desired motor speed.
  	/// Usually in N-m.
  	float32 maxMotorTorque;
  };
  
  /// A revolute joint constrains two bodies to share a common point while they
  /// are free to rotate about the point. The relative rotation about the shared
  /// point is the joint angle. You can limit the relative rotation with
  /// a joint limit that specifies a lower and upper angle. You can use a motor
  /// to drive the relative rotation about the shared point. A maximum motor torque
  /// is provided so that infinite forces are not generated.
  class b2RevoluteJoint : public b2Joint
  {
  public:
  	b2Vec2 GetAnchorA() const;
  	b2Vec2 GetAnchorB() 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; }
  
  	/// Get the reference angle.
  	float32 GetReferenceAngle() const { return m_referenceAngle; }
  
  	/// Get the current joint angle in radians.
  	float32 GetJointAngle() const;
  
  	/// Get the current joint angle speed in radians per second.
  	float32 GetJointSpeed() const;
  
  	/// Is the joint limit enabled?
  	bool IsLimitEnabled() const;
  
  	/// Enable/disable the joint limit.
  	void EnableLimit(bool flag);
  
  	/// Get the lower joint limit in radians.
  	float32 GetLowerLimit() const;
  
  	/// Get the upper joint limit in radians.
  	float32 GetUpperLimit() const;
  
  	/// Set the joint limits in radians.
  	void SetLimits(float32 lower, float32 upper);
  
  	/// Is the joint motor enabled?
  	bool IsMotorEnabled() const;
  
  	/// Enable/disable the joint motor.
  	void EnableMotor(bool flag);
  
  	/// Set the motor speed in radians per second.
  	void SetMotorSpeed(float32 speed);
  
  	/// Get the motor speed in radians per second.
  	float32 GetMotorSpeed() const;
  
  	/// Set the maximum motor torque, usually in N-m.
  	void SetMaxMotorTorque(float32 torque);
  	float32 GetMaxMotorTorque() const { return m_maxMotorTorque; }
  
  	/// Get the reaction force given the inverse time step.
  	/// Unit is N.
  	b2Vec2 GetReactionForce(float32 inv_dt) const;
  
  	/// Get the reaction torque due to the joint limit given the inverse time step.
  	/// Unit is N*m.
  	float32 GetReactionTorque(float32 inv_dt) const;
  
  	/// Get the current motor torque given the inverse time step.
  	/// Unit is N*m.
  	float32 GetMotorTorque(float32 inv_dt) const;
  
  	/// Dump to b2Log.
  	void Dump();
  
  protected:
  	
  	friend class b2Joint;
  	friend class b2GearJoint;
  
  	b2RevoluteJoint(const b2RevoluteJointDef* def);
  
  	void InitVelocityConstraints(const b2SolverData& data);
  	void SolveVelocityConstraints(const b2SolverData& data);
  	bool SolvePositionConstraints(const b2SolverData& data);
  
  	// Solver shared
  	b2Vec2 m_localAnchorA;
  	b2Vec2 m_localAnchorB;
  	b2Vec3 m_impulse;
  	float32 m_motorImpulse;
  
  	bool m_enableMotor;
  	float32 m_maxMotorTorque;
  	float32 m_motorSpeed;
  
  	bool m_enableLimit;
  	float32 m_referenceAngle;
  	float32 m_lowerAngle;
  	float32 m_upperAngle;
  
  	// Solver temp
  	int32 m_indexA;
  	int32 m_indexB;
  	b2Vec2 m_rA;
  	b2Vec2 m_rB;
  	b2Vec2 m_localCenterA;
  	b2Vec2 m_localCenterB;
  	float32 m_invMassA;
  	float32 m_invMassB;
  	float32 m_invIA;
  	float32 m_invIB;
  	b2Mat33 m_mass;			// effective mass for point-to-point constraint.
  	float32 m_motorMass;	// effective mass for motor/limit angular constraint.
  	b2LimitState m_limitState;
  };
  
  inline float32 b2RevoluteJoint::GetMotorSpeed() const
  {
  	return m_motorSpeed;
  }
  
  #endif
  