b2WheelJoint.h

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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_WHEEL_JOINT_H
#define B2_WHEEL_JOINT_H

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

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;
        }

        void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchor, const b2Vec2& axis);

        b2Vec2 localAnchorA;

        b2Vec2 localAnchorB;

        b2Vec2 localAxisA;

        bool enableMotor;

        float32 maxMotorTorque;

        float32 motorSpeed;

        float32 frequencyHz;

        float32 dampingRatio;
};

class b2WheelJoint : public b2Joint
{
public:
        b2Vec2 GetAnchorA() const;
        b2Vec2 GetAnchorB() const;

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

        const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }

        const b2Vec2& GetLocalAnchorB() const  { return m_localAnchorB; }

        const b2Vec2& GetLocalAxisA() const { return m_localXAxisA; }

        float32 GetJointTranslation() const;

        float32 GetJointSpeed() const;

        bool IsMotorEnabled() const;

        void EnableMotor(bool flag);

        void SetMotorSpeed(float32 speed);

        float32 GetMotorSpeed() const;

        void SetMaxMotorTorque(float32 torque);
        float32 GetMaxMotorTorque() const;

        float32 GetMotorTorque(float32 inv_dt) const;

        void SetSpringFrequencyHz(float32 hz);
        float32 GetSpringFrequencyHz() const;

        void SetSpringDampingRatio(float32 ratio);
        float32 GetSpringDampingRatio() const;

        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