axmol/external/Box2D/Dynamics/Joints/b2WheelJoint.h

/*
* 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. You can use a
/// joint limit to restrict the range of motion and a joint motor to drive
/// the rotation or to model rotational friction.
/// This joint is designed for vehicle suspensions.
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;

    /// 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