btMultiBody.h

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/*
 * PURPOSE:
 *   Class representing an articulated rigid body. Stores the body's
 *   current state, allows forces and torques to be set, handles
 *   timestepping and implements Featherstone's algorithm.
 *   
 * COPYRIGHT:
 *   Copyright (C) Stephen Thompson, <stephen@solarflare.org.uk>, 2011-2013
 *   Portions written By Erwin Coumans: connection to LCP solver, various multibody constraints, replacing Eigen math library by Bullet LinearMath and a dedicated 6x6 matrix inverse (solveImatrix)
 *   Portions written By Jakub Stepien: support for multi-DOF constraints, introduction of spatial algebra and several other improvements
 
 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 BT_MULTIBODY_H
#define BT_MULTIBODY_H
 
#include "LinearMath/btScalar.h"
#include "LinearMath/btVector3.h"
#include "LinearMath/btQuaternion.h"
#include "LinearMath/btMatrix3x3.h"
#include "LinearMath/btAlignedObjectArray.h"
 
#ifdef BT_USE_DOUBLE_PRECISION
#define btMultiBodyData btMultiBodyDoubleData
#define btMultiBodyDataName "btMultiBodyDoubleData"
#define btMultiBodyLinkData btMultiBodyLinkDoubleData
#define btMultiBodyLinkDataName "btMultiBodyLinkDoubleData"
#else
#define btMultiBodyData btMultiBodyFloatData
#define btMultiBodyDataName "btMultiBodyFloatData"
#define btMultiBodyLinkData btMultiBodyLinkFloatData
#define btMultiBodyLinkDataName "btMultiBodyLinkFloatData"
#endif  //BT_USE_DOUBLE_PRECISION
 
#include "btMultiBodyLink.h"
class btMultiBodyLinkCollider;
 
ATTRIBUTE_ALIGNED16(class)
btMultiBody
{
public:
    BT_DECLARE_ALIGNED_ALLOCATOR();
 
    //
    // initialization
    //
 
    btMultiBody(int n_links,               // NOT including the base
                btScalar mass,             // mass of base
                const btVector3 &inertia,  // inertia of base, in base frame; assumed diagonal
                bool fixedBase,            // whether the base is fixed (true) or can move (false)
                bool canSleep, bool deprecatedMultiDof = true);
 
    virtual ~btMultiBody();
 
    //note: fixed link collision with parent is always disabled
    void setupFixed(int i, //linkIndex
                    btScalar mass,
                    const btVector3 &inertia,
                    int parent,
                    const btQuaternion &rotParentToThis,
                    const btVector3 &parentComToThisPivotOffset,
                    const btVector3 &thisPivotToThisComOffset, bool deprecatedDisableParentCollision = true);
 
    void setupPrismatic(int i,
                        btScalar mass,
                        const btVector3 &inertia,
                        int parent,
                        const btQuaternion &rotParentToThis,
                        const btVector3 &jointAxis,
                        const btVector3 &parentComToThisPivotOffset,
                        const btVector3 &thisPivotToThisComOffset,
                        bool disableParentCollision);
 
    void setupRevolute(int i,  // 0 to num_links-1
                       btScalar mass,
                       const btVector3 &inertia,
                       int parentIndex,
                       const btQuaternion &rotParentToThis,          // rotate points in parent frame to this frame, when q = 0
                       const btVector3 &jointAxis,                   // in my frame
                       const btVector3 &parentComToThisPivotOffset,  // vector from parent COM to joint axis, in PARENT frame
                       const btVector3 &thisPivotToThisComOffset,    // vector from joint axis to my COM, in MY frame
                       bool disableParentCollision = false);
 
    void setupSpherical(int i,  // linkIndex, 0 to num_links-1
                        btScalar mass,
                        const btVector3 &inertia,
                        int parent,
                        const btQuaternion &rotParentToThis,          // rotate points in parent frame to this frame, when q = 0
                        const btVector3 &parentComToThisPivotOffset,  // vector from parent COM to joint axis, in PARENT frame
                        const btVector3 &thisPivotToThisComOffset,    // vector from joint axis to my COM, in MY frame
                        bool disableParentCollision = false);
 
    void setupPlanar(int i,  // 0 to num_links-1
                     btScalar mass,
                     const btVector3 &inertia,
                     int parent,
                     const btQuaternion &rotParentToThis,  // rotate points in parent frame to this frame, when q = 0
                     const btVector3 &rotationAxis,
                     const btVector3 &parentComToThisComOffset,  // vector from parent COM to this COM, in PARENT frame
                     bool disableParentCollision = false);
 
    const btMultibodyLink &getLink(int index) const
    {
        return m_links[index];
    }
 
    btMultibodyLink &getLink(int index)
    {
        return m_links[index];
    }
 
    void setBaseCollider(btMultiBodyLinkCollider * collider)  //collider can be NULL to disable collision for the base
    {
        m_baseCollider = collider;
    }
    const btMultiBodyLinkCollider *getBaseCollider() const
    {
        return m_baseCollider;
    }
    btMultiBodyLinkCollider *getBaseCollider()
    {
        return m_baseCollider;
    }
 
    const btMultiBodyLinkCollider *getLinkCollider(int index) const
    {
        if (index >= 0 && index < getNumLinks())
        {
            return getLink(index).m_collider;
        }
        return 0;
    }
 
    btMultiBodyLinkCollider *getLinkCollider(int index)
    {
        if (index >= 0 && index < getNumLinks())
        {
            return getLink(index).m_collider;
        }
        return 0;
    }
 
    //
    // get parent
    // input: link num from 0 to num_links-1
    // output: link num from 0 to num_links-1, OR -1 to mean the base.
    //
    int getParent(int link_num) const;
 
    //
    // get number of m_links, masses, moments of inertia
    //
 
    int getNumLinks() const { return m_links.size(); }
    int getNumDofs() const { return m_dofCount; }
    int getNumPosVars() const { return m_posVarCnt; }
    btScalar getBaseMass() const { return m_baseMass; }
    const btVector3 &getBaseInertia() const { return m_baseInertia; }
    btScalar getLinkMass(int i) const;
    const btVector3 &getLinkInertia(int i) const;
 
    //
    // change mass (incomplete: can only change base mass and inertia at present)
    //
 
    void setBaseMass(btScalar mass) { m_baseMass = mass; }
    void setBaseInertia(const btVector3 &inertia) { m_baseInertia = inertia; }
 
    //
    // get/set pos/vel/rot/omega for the base link
    //
 
    const btVector3 &getBasePos() const 
    { 
        return m_basePos; 
    }  // in world frame
    const btVector3 getBaseVel() const
    {
        return btVector3(m_realBuf[3], m_realBuf[4], m_realBuf[5]);
    }  // in world frame
    const btQuaternion &getWorldToBaseRot() const
    {
        return m_baseQuat;
    }
    
    const btVector3 &getInterpolateBasePos() const
    {
        return m_basePos_interpolate;
    }  // in world frame
    const btQuaternion &getInterpolateWorldToBaseRot() const
    {
        return m_baseQuat_interpolate;
    }
    
    // rotates world vectors into base frame
    btVector3 getBaseOmega() const { return btVector3(m_realBuf[0], m_realBuf[1], m_realBuf[2]); }  // in world frame
 
    void setBasePos(const btVector3 &pos)
    {
        m_basePos = pos;
        m_basePos_interpolate = pos;
    }
 
    void setBaseWorldTransform(const btTransform &tr)
    {
        setBasePos(tr.getOrigin());
        setWorldToBaseRot(tr.getRotation().inverse());
    }
 
    btTransform getBaseWorldTransform() const
    {
        btTransform tr;
        tr.setOrigin(getBasePos());
        tr.setRotation(getWorldToBaseRot().inverse());
        return tr;
    }
 
    void setBaseVel(const btVector3 &vel)
    {
        m_realBuf[3] = vel[0];
        m_realBuf[4] = vel[1];
        m_realBuf[5] = vel[2];
    }
    void setWorldToBaseRot(const btQuaternion &rot)
    {
        m_baseQuat = rot;  //m_baseQuat asumed to ba alias!?
        m_baseQuat_interpolate = rot;
    }
    void setBaseOmega(const btVector3 &omega)
    {
        m_realBuf[0] = omega[0];
        m_realBuf[1] = omega[1];
        m_realBuf[2] = omega[2];
    }
 
    //
    // get/set pos/vel for child m_links (i = 0 to num_links-1)
    //
 
    btScalar getJointPos(int i) const;
    btScalar getJointVel(int i) const;
 
    btScalar *getJointVelMultiDof(int i);
    btScalar *getJointPosMultiDof(int i);
 
    const btScalar *getJointVelMultiDof(int i) const;
    const btScalar *getJointPosMultiDof(int i) const;
 
    void setJointPos(int i, btScalar q);
    void setJointVel(int i, btScalar qdot);
    void setJointPosMultiDof(int i, const double *q);
    void setJointVelMultiDof(int i, const double *qdot);
    void setJointPosMultiDof(int i, const float *q);
    void setJointVelMultiDof(int i, const float *qdot);
 
    //
    // direct access to velocities as a vector of 6 + num_links elements.
    // (omega first, then v, then joint velocities.)
    //
    const btScalar *getVelocityVector() const
    {
        return &m_realBuf[0];
    }
    
    const btScalar *getDeltaVelocityVector() const
    {
        return &m_deltaV[0];
    }
    
    const btScalar *getSplitVelocityVector() const
    {
        return &m_splitV[0];
    }
    /*    btScalar * getVelocityVector() 
    { 
        return &real_buf[0]; 
    }
  */
 
    //
    // get the frames of reference (positions and orientations) of the child m_links
    // (i = 0 to num_links-1)
    //
 
    const btVector3 &getRVector(int i) const;              // vector from COM(parent(i)) to COM(i), in frame i's coords
    const btQuaternion &getParentToLocalRot(int i) const;  // rotates vectors in frame parent(i) to vectors in frame i.
    const btVector3 &getInterpolateRVector(int i) const;              // vector from COM(parent(i)) to COM(i), in frame i's coords
    const btQuaternion &getInterpolateParentToLocalRot(int i) const;  // rotates vectors in frame parent(i) to vectors in frame i.
 
    //
    // transform vectors in local frame of link i to world frame (or vice versa)
    //
    btVector3 localPosToWorld(int i, const btVector3 &local_pos) const;
    btVector3 localDirToWorld(int i, const btVector3 &local_dir) const;
    btVector3 worldPosToLocal(int i, const btVector3 &world_pos) const;
    btVector3 worldDirToLocal(int i, const btVector3 &world_dir) const;
 
    //
    // transform a frame in local coordinate to a frame in world coordinate
    //
    btMatrix3x3 localFrameToWorld(int i, const btMatrix3x3 &local_frame) const;
 
 
    //
    // set external forces and torques. Note all external forces/torques are given in the WORLD frame.
    //
 
    void clearForcesAndTorques();
    void clearConstraintForces();
 
    void clearVelocities();
 
    void addBaseForce(const btVector3 &f)
    {
        m_baseForce += f;
    }
    void addBaseTorque(const btVector3 &t) { m_baseTorque += t; }
    void addLinkForce(int i, const btVector3 &f);
    void addLinkTorque(int i, const btVector3 &t);
 
    void addBaseConstraintForce(const btVector3 &f)
    {
        m_baseConstraintForce += f;
    }
    void addBaseConstraintTorque(const btVector3 &t) { m_baseConstraintTorque += t; }
    void addLinkConstraintForce(int i, const btVector3 &f);
    void addLinkConstraintTorque(int i, const btVector3 &t);
 
    void addJointTorque(int i, btScalar Q);
    void addJointTorqueMultiDof(int i, int dof, btScalar Q);
    void addJointTorqueMultiDof(int i, const btScalar *Q);
 
    const btVector3 &getBaseForce() const { return m_baseForce; }
    const btVector3 &getBaseTorque() const { return m_baseTorque; }
    const btVector3 &getLinkForce(int i) const;
    const btVector3 &getLinkTorque(int i) const;
    btScalar getJointTorque(int i) const;
    btScalar *getJointTorqueMultiDof(int i);
 
    //
    // dynamics routines.
    //
 
    // timestep the velocities (given the external forces/torques set using addBaseForce etc).
    // also sets up caches for calcAccelerationDeltas.
    //
    // Note: the caller must provide three vectors which are used as
    // temporary scratch space. The idea here is to reduce dynamic
    // memory allocation: the same scratch vectors can be re-used
    // again and again for different Multibodies, instead of each
    // btMultiBody allocating (and then deallocating) their own
    // individual scratch buffers. This gives a considerable speed
    // improvement, at least on Windows (where dynamic memory
    // allocation appears to be fairly slow).
    //
 
    void computeAccelerationsArticulatedBodyAlgorithmMultiDof(btScalar dt,
                                                              btAlignedObjectArray<btScalar> & scratch_r,
                                                              btAlignedObjectArray<btVector3> & scratch_v,
                                                              btAlignedObjectArray<btMatrix3x3> & scratch_m,
                                                              bool isConstraintPass,
                                                              bool jointFeedbackInWorldSpace,
                                                              bool jointFeedbackInJointFrame
                                                              );
 
    //void stepVelocitiesMultiDof(btScalar dt,
    //                          btAlignedObjectArray<btScalar> & scratch_r,
    //                          btAlignedObjectArray<btVector3> & scratch_v,
    //                          btAlignedObjectArray<btMatrix3x3> & scratch_m,
    //                          bool isConstraintPass = false)
    //{
    //  computeAccelerationsArticulatedBodyAlgorithmMultiDof(dt, scratch_r, scratch_v, scratch_m, isConstraintPass, false, false);
    //}
 
    // calcAccelerationDeltasMultiDof
    // input: force vector (in same format as jacobian, i.e.:
    //                      3 torque values, 3 force values, num_links joint torque values)
    // output: 3 omegadot values, 3 vdot values, num_links q_double_dot values
    // (existing contents of output array are replaced)
    // calcAccelerationDeltasMultiDof must have been called first.
    void calcAccelerationDeltasMultiDof(const btScalar *force, btScalar *output,
                                        btAlignedObjectArray<btScalar> &scratch_r,
                                        btAlignedObjectArray<btVector3> &scratch_v) const;
 
    void applyDeltaVeeMultiDof2(const btScalar *delta_vee, btScalar multiplier)
    {
        for (int dof = 0; dof < 6 + getNumDofs(); ++dof)
        {
            m_deltaV[dof] += delta_vee[dof] * multiplier;
        }
    }
    void applyDeltaSplitVeeMultiDof(const btScalar *delta_vee, btScalar multiplier)
    {
        for (int dof = 0; dof < 6 + getNumDofs(); ++dof)
        {
            m_splitV[dof] += delta_vee[dof] * multiplier;
        }
    }
    void addSplitV()
    {
        applyDeltaVeeMultiDof(&m_splitV[0], 1);
    }
    void substractSplitV()
    {
        applyDeltaVeeMultiDof(&m_splitV[0], -1);
        
        for (int dof = 0; dof < 6 + getNumDofs(); ++dof)
        {
            m_splitV[dof] = 0.f;
        }
    }
    void processDeltaVeeMultiDof2()
    {
        applyDeltaVeeMultiDof(&m_deltaV[0], 1);
 
        for (int dof = 0; dof < 6 + getNumDofs(); ++dof)
        {
            m_deltaV[dof] = 0.f;
        }
    }
 
    void applyDeltaVeeMultiDof(const btScalar *delta_vee, btScalar multiplier)
    {
        //for (int dof = 0; dof < 6 + getNumDofs(); ++dof)
        //  printf("%.4f ", delta_vee[dof]*multiplier);
        //printf("\n");
 
        //btScalar sum = 0;
        //for (int dof = 0; dof < 6 + getNumDofs(); ++dof)
        //{
        //  sum += delta_vee[dof]*multiplier*delta_vee[dof]*multiplier;
        //}
        //btScalar l = btSqrt(sum);
 
        //if (l>m_maxAppliedImpulse)
        //{
        //  multiplier *= m_maxAppliedImpulse/l;
        //}
 
        for (int dof = 0; dof < 6 + getNumDofs(); ++dof)
        {
            m_realBuf[dof] += delta_vee[dof] * multiplier;
            btClamp(m_realBuf[dof], -m_maxCoordinateVelocity, m_maxCoordinateVelocity);
        }
    }
 
    // timestep the positions (given current velocities).
    void stepPositionsMultiDof(btScalar dt, btScalar *pq = 0, btScalar *pqd = 0);
    
    // predict the positions
    void predictPositionsMultiDof(btScalar dt);
 
    //
    // contacts
    //
 
    // This routine fills out a contact constraint jacobian for this body.
    // the 'normal' supplied must be -n for body1 or +n for body2 of the contact.
    // 'normal' & 'contact_point' are both given in world coordinates.
 
    void fillContactJacobianMultiDof(int link,
                                     const btVector3 &contact_point,
                                     const btVector3 &normal,
                                     btScalar *jac,
                                     btAlignedObjectArray<btScalar> &scratch_r,
                                     btAlignedObjectArray<btVector3> &scratch_v,
                                     btAlignedObjectArray<btMatrix3x3> &scratch_m) const { fillConstraintJacobianMultiDof(link, contact_point, btVector3(0, 0, 0), normal, jac, scratch_r, scratch_v, scratch_m); }
 
    //a more general version of fillContactJacobianMultiDof which does not assume..
    //.. that the constraint in question is contact or, to be more precise, constrains linear velocity only
    void fillConstraintJacobianMultiDof(int link,
                                        const btVector3 &contact_point,
                                        const btVector3 &normal_ang,
                                        const btVector3 &normal_lin,
                                        btScalar *jac,
                                        btAlignedObjectArray<btScalar> &scratch_r,
                                        btAlignedObjectArray<btVector3> &scratch_v,
                                        btAlignedObjectArray<btMatrix3x3> &scratch_m) const;
 
    //
    // sleeping
    //
    void setCanSleep(bool canSleep)
    {
        if (m_canWakeup)
        {
            m_canSleep = canSleep;
        }
    }
 
    bool getCanSleep() const
    {
        return m_canSleep;
    }
 
    bool getCanWakeup() const
    {
        return m_canWakeup;
    }
    
    void setCanWakeup(bool canWakeup) 
    {
        m_canWakeup = canWakeup;
    }
    bool isAwake() const { return m_awake; }
    void wakeUp();
    void goToSleep();
    void checkMotionAndSleepIfRequired(btScalar timestep);
 
    bool hasFixedBase() const
    {
        return m_fixedBase;
    }
 
    void setFixedBase(bool fixedBase)
    {
        m_fixedBase = fixedBase;
    }
 
    int getCompanionId() const
    {
        return m_companionId;
    }
    void setCompanionId(int id)
    {
        //printf("for %p setCompanionId(%d)\n",this, id);
        m_companionId = id;
    }
 
    void setNumLinks(int numLinks)  //careful: when changing the number of m_links, make sure to re-initialize or update existing m_links
    {
        m_links.resize(numLinks);
    }
 
    btScalar getLinearDamping() const
    {
        return m_linearDamping;
    }
    void setLinearDamping(btScalar damp)
    {
        m_linearDamping = damp;
    }
    btScalar getAngularDamping() const
    {
        return m_angularDamping;
    }
    void setAngularDamping(btScalar damp)
    {
        m_angularDamping = damp;
    }
 
    bool getUseGyroTerm() const
    {
        return m_useGyroTerm;
    }
    void setUseGyroTerm(bool useGyro)
    {
        m_useGyroTerm = useGyro;
    }
    btScalar getMaxCoordinateVelocity() const
    {
        return m_maxCoordinateVelocity;
    }
    void setMaxCoordinateVelocity(btScalar maxVel)
    {
        m_maxCoordinateVelocity = maxVel;
    }
 
    btScalar getMaxAppliedImpulse() const
    {
        return m_maxAppliedImpulse;
    }
    void setMaxAppliedImpulse(btScalar maxImp)
    {
        m_maxAppliedImpulse = maxImp;
    }
    void setHasSelfCollision(bool hasSelfCollision)
    {
        m_hasSelfCollision = hasSelfCollision;
    }
    bool hasSelfCollision() const
    {
        return m_hasSelfCollision;
    }
 
    void finalizeMultiDof();
 
    void useRK4Integration(bool use) { m_useRK4 = use; }
    bool isUsingRK4Integration() const { return m_useRK4; }
    void useGlobalVelocities(bool use) { m_useGlobalVelocities = use; }
    bool isUsingGlobalVelocities() const { return m_useGlobalVelocities; }
 
    bool isPosUpdated() const
    {
        return __posUpdated;
    }
    void setPosUpdated(bool updated)
    {
        __posUpdated = updated;
    }
 
    //internalNeedsJointFeedback is for internal use only
    bool internalNeedsJointFeedback() const
    {
        return m_internalNeedsJointFeedback;
    }
    void forwardKinematics(btAlignedObjectArray<btQuaternion>& world_to_local, btAlignedObjectArray<btVector3> & local_origin);
 
    void compTreeLinkVelocities(btVector3 * omega, btVector3 * vel) const;
 
    void updateCollisionObjectWorldTransforms(btAlignedObjectArray<btQuaternion> & world_to_local, btAlignedObjectArray<btVector3> & local_origin);
    void updateCollisionObjectInterpolationWorldTransforms(btAlignedObjectArray<btQuaternion> & world_to_local, btAlignedObjectArray<btVector3> & local_origin);
 
    virtual int calculateSerializeBufferSize() const;
 
    virtual const char *serialize(void *dataBuffer, class btSerializer *serializer) const;
 
    const char *getBaseName() const
    {
        return m_baseName;
    }
    void setBaseName(const char *name)
    {
        m_baseName = name;
    }
 
    void *getUserPointer() const
    {
        return m_userObjectPointer;
    }
 
    int getUserIndex() const
    {
        return m_userIndex;
    }
 
    int getUserIndex2() const
    {
        return m_userIndex2;
    }
    void setUserPointer(void *userPointer)
    {
        m_userObjectPointer = userPointer;
    }
 
    void setUserIndex(int index)
    {
        m_userIndex = index;
    }
 
    void setUserIndex2(int index)
    {
        m_userIndex2 = index;
    }
 
    static void spatialTransform(const btMatrix3x3 &rotation_matrix,  // rotates vectors in 'from' frame to vectors in 'to' frame
        const btVector3 &displacement,     // vector from origin of 'from' frame to origin of 'to' frame, in 'to' coordinates
        const btVector3 &top_in,       // top part of input vector
        const btVector3 &bottom_in,    // bottom part of input vector
        btVector3 &top_out,         // top part of output vector
        btVector3 &bottom_out);      // bottom part of output vector
 
 
 
private:
    btMultiBody(const btMultiBody &);     // not implemented
    void operator=(const btMultiBody &);  // not implemented
 
    void solveImatrix(const btVector3 &rhs_top, const btVector3 &rhs_bot, btScalar result[6]) const;
    void solveImatrix(const btSpatialForceVector &rhs, btSpatialMotionVector &result) const;
 
    void updateLinksDofOffsets()
    {
        int dofOffset = 0, cfgOffset = 0;
        for (int bidx = 0; bidx < m_links.size(); ++bidx)
        {
            m_links[bidx].m_dofOffset = dofOffset;
            m_links[bidx].m_cfgOffset = cfgOffset;
            dofOffset += m_links[bidx].m_dofCount;
            cfgOffset += m_links[bidx].m_posVarCount;
        }
    }
 
    void mulMatrix(btScalar * pA, btScalar * pB, int rowsA, int colsA, int rowsB, int colsB, btScalar *pC) const;
 
private:
    btMultiBodyLinkCollider *m_baseCollider;  //can be NULL
    const char *m_baseName;                   //memory needs to be manager by user!
 
    btVector3 m_basePos;      // position of COM of base (world frame)
    btVector3 m_basePos_interpolate;      // position of interpolated COM of base (world frame)
    btQuaternion m_baseQuat;  // rotates world points into base frame
    btQuaternion m_baseQuat_interpolate;  
 
    btScalar m_baseMass;      // mass of the base
    btVector3 m_baseInertia;  // inertia of the base (in local frame; diagonal)
 
    btVector3 m_baseForce;   // external force applied to base. World frame.
    btVector3 m_baseTorque;  // external torque applied to base. World frame.
 
    btVector3 m_baseConstraintForce;   // external force applied to base. World frame.
    btVector3 m_baseConstraintTorque;  // external torque applied to base. World frame.
 
    btAlignedObjectArray<btMultibodyLink> m_links;  // array of m_links, excluding the base. index from 0 to num_links-1.
 
    //
    // realBuf:
    //  offset         size            array
    //   0              6 + num_links   v (base_omega; base_vel; joint_vels)                    MULTIDOF [sysdof x sysdof for D matrices (TOO MUCH!) + pos_delta which is sys-cfg sized]
    //   6+num_links    num_links       D
    //
    // vectorBuf:
    //  offset         size         array
    //   0              num_links    h_top
    //   num_links      num_links    h_bottom
    //
    // matrixBuf:
    //  offset         size         array
    //   0              num_links+1  rot_from_parent
    //
    btAlignedObjectArray<btScalar> m_splitV;
    btAlignedObjectArray<btScalar> m_deltaV;
    btAlignedObjectArray<btScalar> m_realBuf;
    btAlignedObjectArray<btVector3> m_vectorBuf;
    btAlignedObjectArray<btMatrix3x3> m_matrixBuf;
 
    btMatrix3x3 m_cachedInertiaTopLeft;
    btMatrix3x3 m_cachedInertiaTopRight;
    btMatrix3x3 m_cachedInertiaLowerLeft;
    btMatrix3x3 m_cachedInertiaLowerRight;
    bool m_cachedInertiaValid;
 
    bool m_fixedBase;
 
    // Sleep parameters.
    bool m_awake;
    bool m_canSleep;
    bool m_canWakeup;
    btScalar m_sleepTimer;
 
    void *m_userObjectPointer;
    int m_userIndex2;
    int m_userIndex;
 
    int m_companionId;
    btScalar m_linearDamping;
    btScalar m_angularDamping;
    bool m_useGyroTerm;
    btScalar m_maxAppliedImpulse;
    btScalar m_maxCoordinateVelocity;
    bool m_hasSelfCollision;
 
    bool __posUpdated;
    int m_dofCount, m_posVarCnt;
 
    bool m_useRK4, m_useGlobalVelocities;
    //for global velocities, see 8.3.2B Proposed resolution in Jakub Stepien PhD Thesis
    //https://drive.google.com/file/d/0Bz3vEa19XOYGNWdZWGpMdUdqVmZ5ZVBOaEh4ZnpNaUxxZFNV/view?usp=sharing
 
    bool m_internalNeedsJointFeedback;
};
 
struct btMultiBodyLinkDoubleData
{
    btQuaternionDoubleData m_zeroRotParentToThis;
    btVector3DoubleData m_parentComToThisPivotOffset;
    btVector3DoubleData m_thisPivotToThisComOffset;
    btVector3DoubleData m_jointAxisTop[6];
    btVector3DoubleData m_jointAxisBottom[6];
 
    btVector3DoubleData m_linkInertia;  // inertia of the base (in local frame; diagonal)
    btVector3DoubleData m_absFrameTotVelocityTop;
    btVector3DoubleData m_absFrameTotVelocityBottom;
    btVector3DoubleData m_absFrameLocVelocityTop;
    btVector3DoubleData m_absFrameLocVelocityBottom;
 
    double m_linkMass;
    int m_parentIndex;
    int m_jointType;
 
    int m_dofCount;
    int m_posVarCount;
    double m_jointPos[7];
    double m_jointVel[6];
    double m_jointTorque[6];
 
    double m_jointDamping;
    double m_jointFriction;
    double m_jointLowerLimit;
    double m_jointUpperLimit;
    double m_jointMaxForce;
    double m_jointMaxVelocity;
 
    char *m_linkName;
    char *m_jointName;
    btCollisionObjectDoubleData *m_linkCollider;
    char *m_paddingPtr;
};
 
struct btMultiBodyLinkFloatData
{
    btQuaternionFloatData m_zeroRotParentToThis;
    btVector3FloatData m_parentComToThisPivotOffset;
    btVector3FloatData m_thisPivotToThisComOffset;
    btVector3FloatData m_jointAxisTop[6];
    btVector3FloatData m_jointAxisBottom[6];
    btVector3FloatData m_linkInertia;  // inertia of the base (in local frame; diagonal)
    btVector3FloatData m_absFrameTotVelocityTop;
    btVector3FloatData m_absFrameTotVelocityBottom;
    btVector3FloatData m_absFrameLocVelocityTop;
    btVector3FloatData m_absFrameLocVelocityBottom;
 
    int m_dofCount;
    float m_linkMass;
    int m_parentIndex;
    int m_jointType;
 
    float m_jointPos[7];
    float m_jointVel[6];
    float m_jointTorque[6];
    int m_posVarCount;
    float m_jointDamping;
    float m_jointFriction;
    float m_jointLowerLimit;
    float m_jointUpperLimit;
    float m_jointMaxForce;
    float m_jointMaxVelocity;
 
    char *m_linkName;
    char *m_jointName;
    btCollisionObjectFloatData *m_linkCollider;
    char *m_paddingPtr;
};
 
struct btMultiBodyDoubleData
{
    btVector3DoubleData m_baseWorldPosition;
    btQuaternionDoubleData m_baseWorldOrientation;
    btVector3DoubleData m_baseLinearVelocity;
    btVector3DoubleData m_baseAngularVelocity;
    btVector3DoubleData m_baseInertia;  // inertia of the base (in local frame; diagonal)
    double m_baseMass;
    int m_numLinks;
    char m_padding[4];
 
    char *m_baseName;
    btMultiBodyLinkDoubleData *m_links;
    btCollisionObjectDoubleData *m_baseCollider;
};
 
struct btMultiBodyFloatData
{
    btVector3FloatData m_baseWorldPosition;
    btQuaternionFloatData m_baseWorldOrientation;
    btVector3FloatData m_baseLinearVelocity;
    btVector3FloatData m_baseAngularVelocity;
 
    btVector3FloatData m_baseInertia;  // inertia of the base (in local frame; diagonal)
    float m_baseMass;
    int m_numLinks;
 
    char *m_baseName;
    btMultiBodyLinkFloatData *m_links;
    btCollisionObjectFloatData *m_baseCollider;
};
 
#endif