axmol/Box2D/Dynamics/Joints/b2WeldJoint.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_WELD_JOINT_H
#define B2_WELD_JOINT_H

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

/// Weld joint definition. You need to specify local anchor points
/// where they are attached and the relative body angle. The position
/// of the anchor points is important for computing the reaction torque.
struct b2WeldJointDef : public b2JointDef
{
    b2WeldJointDef()
    {
        type = e_weldJoint;
        localAnchorA.Set(0.0f, 0.0f);
        localAnchorB.Set(0.0f, 0.0f);
        referenceAngle = 0.0f;
        frequencyHz = 0.0f;
        dampingRatio = 0.0f;
    }

    /// Initialize the bodies, anchors, and reference angle using a world
    /// anchor point.
    void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchor);

    /// The local anchor point relative to bodyA's origin.
    b2Vec2 localAnchorA;

    /// The local anchor point relative to bodyB's origin.
    b2Vec2 localAnchorB;

    /// The bodyB angle minus bodyA angle in the reference state (radians).
    float32 referenceAngle;
    
    /// The mass-spring-damper frequency in Hertz. Rotation only.
    /// Disable softness with a value of 0.
    float32 frequencyHz;

    /// The damping ratio. 0 = no damping, 1 = critical damping.
    float32 dampingRatio;
};

/// A weld joint essentially glues two bodies together. A weld joint may
/// distort somewhat because the island constraint solver is approximate.
class b2WeldJoint : 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; }

    /// Get the reference angle.
    float32 GetReferenceAngle() const { return m_referenceAngle; }

    /// Set/get frequency in Hz.
    void SetFrequency(float32 hz) { m_frequencyHz = hz; }
    float32 GetFrequency() const { return m_frequencyHz; }

    /// Set/get damping ratio.
    void SetDampingRatio(float32 ratio) { m_dampingRatio = ratio; }
    float32 GetDampingRatio() const { return m_dampingRatio; }

    /// Dump to b2Log
    void Dump();

protected:

    friend class b2Joint;

    b2WeldJoint(const b2WeldJointDef* def);

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

    float32 m_frequencyHz;
    float32 m_dampingRatio;
    float32 m_bias;

    // Solver shared
    b2Vec2 m_localAnchorA;
    b2Vec2 m_localAnchorB;
    float32 m_referenceAngle;
    float32 m_gamma;
    b2Vec3 m_impulse;

    // Solver temp
    int32 m_indexA;
    int32 m_indexB;
    b2Vec2 m_rA;
    b2Vec2 m_rB;
    b2Vec2 m_localCenterA;
    b2Vec2 m_localCenterB;
    float32 m_invMassA;
    float32 m_invMassB;
    float32 m_invIA;
    float32 m_invIB;
    b2Mat33 m_mass;
};

#endif