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Bullet Continuous Collision Detection and Physics Library
Copyright (c) 2003-2006 Erwin Coumans  http://continuousphysics.com/Bullet/

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.


#include "SimdVector3.h"
#include "Dynamics/RigidBody.h"

// Another memory optimization would be to store m_1MinvJt in the remaining 3 w components
// which makes the JacobianEntry memory layout 16 bytes
// if you only are interested in angular part, just feed massInvA and massInvB zero

/// Jacobian entry is an abstraction that allows to describe constraints
/// it can be used in combination with a constraint solver
/// Can be used to relate the effect of an impulse to the constraint error
00031 class JacobianEntry
      JacobianEntry() {};
      //constraint between two different rigidbodies
            const SimdMatrix3x3& world2A,
            const SimdMatrix3x3& world2B,
            const SimdVector3& rel_pos1,const SimdVector3& rel_pos2,
            const SimdVector3& jointAxis,
            const SimdVector3& inertiaInvA, 
            const SimdScalar massInvA,
            const SimdVector3& inertiaInvB,
            const SimdScalar massInvB)
            m_aJ = world2A*(rel_pos1.cross(m_jointAxis));
            m_bJ = world2B*(rel_pos2.cross(-m_jointAxis));
            m_0MinvJt   = inertiaInvA * m_aJ;
            m_1MinvJt = inertiaInvB * m_bJ;
            m_Adiag = massInvA + m_0MinvJt.dot(m_aJ) + massInvB + m_1MinvJt.dot(m_bJ);

            //angular constraint between two different rigidbodies
      JacobianEntry(const SimdVector3& jointAxis,
            const SimdMatrix3x3& world2A,
            const SimdMatrix3x3& world2B,
            const SimdVector3& inertiaInvA,
            const SimdVector3& inertiaInvB)
            m_aJ= world2A*m_jointAxis;
            m_bJ = world2B*-m_jointAxis;
            m_0MinvJt   = inertiaInvA * m_aJ;
            m_1MinvJt = inertiaInvB * m_bJ;
            m_Adiag =  m_0MinvJt.dot(m_aJ) + m_1MinvJt.dot(m_bJ);

      //constraint on one rigidbody
            const SimdMatrix3x3& world2A,
            const SimdVector3& rel_pos1,const SimdVector3& rel_pos2,
            const SimdVector3& jointAxis,
            const SimdVector3& inertiaInvA, 
            const SimdScalar massInvA)
            m_aJ= world2A*(rel_pos1.cross(m_jointAxis));
            m_bJ = world2A*(rel_pos2.cross(-m_jointAxis));
            m_0MinvJt   = inertiaInvA * m_aJ;
            m_1MinvJt = SimdVector3(0.f,0.f,0.f);
            m_Adiag = massInvA + m_0MinvJt.dot(m_aJ);

      SimdScalar  getDiagonal() const { return m_Adiag; }

      // for two constraints on the same rigidbody (for example vehicle friction)
      SimdScalar  getNonDiagonal(const JacobianEntry& jacB, const SimdScalar massInvA) const
            const JacobianEntry& jacA = *this;
            SimdScalar lin = massInvA * jacA.m_jointAxis.dot(jacB.m_jointAxis);
            SimdScalar ang = jacA.m_0MinvJt.dot(jacB.m_aJ);
            return lin + ang;


      // for two constraints on sharing two same rigidbodies (for example two contact points between two rigidbodies)
      SimdScalar  getNonDiagonal(const JacobianEntry& jacB,const SimdScalar massInvA,const SimdScalar massInvB) const
            const JacobianEntry& jacA = *this;
            SimdVector3 lin = jacA.m_jointAxis* jacB.m_jointAxis;
            SimdVector3 ang0 = jacA.m_0MinvJt * jacB.m_aJ;
            SimdVector3 ang1 = jacA.m_1MinvJt * jacB.m_bJ;
            SimdVector3 lin0 = massInvA * lin ;
            SimdVector3 lin1 = massInvB * lin;
            SimdVector3 sum = ang0+ang1+lin0+lin1;
            return sum[0]+sum[1]+sum[2];

      SimdScalar getRelativeVelocity(const SimdVector3& linvelA,const SimdVector3& angvelA,const SimdVector3& linvelB,const SimdVector3& angvelB)
            SimdVector3 linrel = linvelA - linvelB;
            SimdVector3 angvela  = angvelA * m_aJ;
            SimdVector3 angvelb  = angvelB * m_bJ;
            linrel *= m_jointAxis;
            angvela += angvelb;
            angvela += linrel;
            SimdScalar rel_vel2 = angvela[0]+angvela[1]+angvela[2];
            return rel_vel2 + SIMD_EPSILON;

      SimdVector3 m_jointAxis;
      SimdVector3 m_aJ;
      SimdVector3 m_bJ;
      SimdVector3 m_0MinvJt;
      SimdVector3 m_1MinvJt;
      //Optimization: can be stored in the w/last component of one of the vectors
      SimdScalar  m_Adiag;



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