cocos2d-x节点（b2WheelJoint.h)API

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cocos2d-x节点（b2WheelJoint.h)API

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/// 一个Wheel（车轮）joints（接头）这个 joints（接头）提供了两个自由度:沿固定在 bodyA上的轴和平面旋转

///cocos2d-x-3.0alpha0/external/Box2D/Dynamics/Joints
/// 一个Wheel（车轮）joints（接头）这个 joints（接头）提供了两个自由度:沿固定在 bodyA上的轴和平面旋转


#ifndef B2_WHEEL_JOINT_H
#define B2_WHEEL_JOINT_H

#include <Box2D/Dynamics/Joints/b2Joint.h>

/// Wheel（车轮）joints（接头）定义. 这个定义需要 运动的线使用的轴和锚点
/// 定义使用本地锚点和本地轴，所以初始配置可以稍微违反约束。
/// 当本地锚点和 world 空间里的锚点重合时，joints（接头）换算成 0。
//使用本地锚点和本地轴有助于保存和加载游戏时
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);

    /// 相对与 bodyA's 原点本地锚点.
    b2Vec2 localAnchorA;

    /// 相对与 bodyB's 原点的本地锚点.
    b2Vec2 localAnchorB;

    /// bodyA 上面的本地换算轴.
    b2Vec2 localAxisA;

    /// Enable/disable the joint motor.
    bool enableMotor;

    /// The maximum motor torque（力矩）, usually in N-m.       //电机
    float32 maxMotorTorque;

    /// The desired（期望的） motor speed in radians per second.      //电机
    float32 motorSpeed;

    /// Suspension frequency, zero indicates no suspension      //悬浮频率，零表示没有悬浮
    float32 frequencyHz;

    /// Suspension damping ratio, one indicates critical damping    //悬浮阻尼比，一表示临界阻尼
    float32 dampingRatio;
};

/// 一个Wheel（车轮）joints（接头）这个 joints（接头）提供了两个自由度:沿固定在 bodyA上的轴和平面旋转
/// 你可以使用joints（接头）来限制运动的摩擦范围，一个joints（接头）motor 来驱动旋转或者旋转摩擦模型        //电机
/// 这个 joint（接头）是为 Wheel（车轮）的悬浮而设计的
class b2WheelJoint : public b2Joint
{
public:
    void GetDefinition(b2WheelJointDef* def) const;

    b2Vec2 GetAnchorA() const;
    b2Vec2 GetAnchorB() const;

    b2Vec2 GetReactionForce(float32 inv_dt) const;
    float32 GetReactionTorque(float32 inv_dt) const;

    /// 相对与 bodyA's 的原点本地锚点.
    const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }

    /// 相对与 bodyB's 原点的本地锚点.
    const b2Vec2& GetLocalAnchorB() const  { return m_localAnchorB; }

    /// bodyA 上面的本地换算轴.
    const b2Vec2& GetLocalAxisA() const { return m_localXAxisA; }

    /// Get the current joint translation(换算), usually in meters.
    float32 GetJointTranslation() const;

    /// Get the current joint translation（换算） speed, usually in meters per second.
    float32 GetJointSpeed() const;

    /// Is the joint motor enabled?         //电机
    bool IsMotorEnabled() const;

    /// Enable/disable the joint motor.
    void EnableMotor(bool flag);

    /// Set the motor speed, usually in radians per second.        //电机
    void SetMotorSpeed(float32 speed);

    /// Get the motor speed, usually in radians per second.        //电机
    float32 GetMotorSpeed() const;

    /// Set/Get the maximum motor force(力), usually in N-m.        //电机
    void SetMaxMotorTorque(float32 torque);
    float32 GetMaxMotorTorque() const;

    /// Get the current motor torque given the inverse time step, usually in N-m.   //逆转时间步获取当前 motor 力        //电机
    float32 GetMotorTorque(float32 inv_dt) const;

    /// Set/Get the spring frequency in hertz. Setting the frequency to zero disables the spring.       //弹簧的频率，单位为赫兹。频率设定为零禁用弹性
    void SetSpringFrequencyHz(float32 hz);
    float32 GetSpringFrequencyHz() const;

    /// Set/Get the spring damping ratio        //弹簧阻尼系数
    void SetSpringDampingRatio(float32 ratio);
    float32 GetSpringDampingRatio() const;

    ///把阻尼输出到 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