axmol/Box2D/Dynamics/Joints/b2PrismaticJoint.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_PRISMATIC_JOINT_H
#define B2_PRISMATIC_JOINT_H

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

/// Prismatic 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 b2PrismaticJointDef : public b2JointDef
{
    b2PrismaticJointDef()
    {
        type = e_prismaticJoint;
        localAnchorA.SetZero();
        localAnchorB.SetZero();
        localAxisA.Set(1.0f, 0.0f);
        referenceAngle = 0.0f;
        enableLimit = false;
        lowerTranslation = 0.0f;
        upperTranslation = 0.0f;
        enableMotor = false;
        maxMotorForce = 0.0f;
        motorSpeed = 0.0f;
    }

    /// Initialize the bodies, anchors, axis, and reference angle using the world
    /// anchor and unit 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 unit axis in bodyA.
    b2Vec2 localAxisA;

    /// The constrained angle between the bodies: bodyB_angle - bodyA_angle.
    float32 referenceAngle;

    /// Enable/disable the joint limit.
    bool enableLimit;

    /// The lower translation limit, usually in meters.
    float32 lowerTranslation;

    /// The upper translation limit, usually in meters.
    float32 upperTranslation;

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

    /// The maximum motor torque, usually in N-m.
    float32 maxMotorForce;

    /// The desired motor speed in radians per second.
    float32 motorSpeed;
};

/// A prismatic joint. This joint provides one degree of freedom: translation
/// along an axis fixed in bodyA. Relative rotation is prevented. You can
/// use a joint limit to restrict the range of motion and a joint motor to
/// drive the motion or to model joint friction.
class b2PrismaticJoint : 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 reference angle.
    float32 GetReferenceAngle() const { return m_referenceAngle; }

    /// 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 limit enabled?
    bool IsLimitEnabled() const;

    /// Enable/disable the joint limit.
    void EnableLimit(bool flag);

    /// Get the lower joint limit, usually in meters.
    float32 GetLowerLimit() const;

    /// Get the upper joint limit, usually in meters.
    float32 GetUpperLimit() const;

    /// Set the joint limits, usually in meters.
    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, usually in meters per second.
    void SetMotorSpeed(float32 speed);

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

    /// Set the maximum motor force, usually in N.
    void SetMaxMotorForce(float32 force);
    float32 GetMaxMotorForce() const { return m_maxMotorForce; }

    /// Get the current motor force given the inverse time step, usually in N.
    float32 GetMotorForce(float32 inv_dt) const;

    /// Dump to b2Log
    void Dump();

protected:
    friend class b2Joint;
    friend class b2GearJoint;
    b2PrismaticJoint(const b2PrismaticJointDef* def);

    void InitVelocityConstraints(const b2SolverData& data);
    void SolveVelocityConstraints(const b2SolverData& data);
    bool SolvePositionConstraints(const b2SolverData& data);

    // Solver shared
    b2Vec2 m_localAnchorA;
    b2Vec2 m_localAnchorB;
    b2Vec2 m_localXAxisA;
    b2Vec2 m_localYAxisA;
    float32 m_referenceAngle;
    b2Vec3 m_impulse;
    float32 m_motorImpulse;
    float32 m_lowerTranslation;
    float32 m_upperTranslation;
    float32 m_maxMotorForce;
    float32 m_motorSpeed;
    bool m_enableLimit;
    bool m_enableMotor;
    b2LimitState m_limitState;

    // 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_axis, m_perp;
    float32 m_s1, m_s2;
    float32 m_a1, m_a2;
    b2Mat33 m_K;
    float32 m_motorMass;
};

inline float32 b2PrismaticJoint::GetMotorSpeed() const
{
    return m_motorSpeed;
}

#endif