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 /*
 * 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