File indexing completed on 2024-12-29 03:29:29

 /*
 * 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. In other words, it is a point to
 /// line constraint with a rotational motor and a linear spring/damper.
 /// 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