Exemplo n.º 1
0
        // Update is called once per frame
        public void Update()
        {
            lock (lck)
            {
                if (mustUpdateTransform)
                {
                    UnityEngine.Vector3    position = BSExtensionMethods2.ExtractTranslationFromMatrix(ref lastBulletTransform.Transform);
                    UnityEngine.Quaternion rotation = BSExtensionMethods2.ExtractRotationFromMatrix(ref lastBulletTransform.Transform);
                    // Interpolation is needed in threaded mode
                    // Maybe we can have a call to the physics engine in an update method instead ?
                    if (threadHelper != null && previousBulletTransform != null)
                    {
                        double currentTime = threadHelper.TotalSimulationTime;
                        UnityEngine.Vector3    previousPosition = BSExtensionMethods2.ExtractTranslationFromMatrix(ref previousBulletTransform.Transform);
                        UnityEngine.Quaternion previousRotation = BSExtensionMethods2.ExtractRotationFromMatrix(ref previousBulletTransform.Transform);

                        double interpolationFactor = (currentTime - lastBulletTransform.TimeStamp) / (lastBulletTransform.TimeStamp - previousBulletTransform.TimeStamp);

                        transform.position = UnityEngine.Vector3.LerpUnclamped(previousPosition, position, (float)interpolationFactor);
                        transform.rotation = UnityEngine.Quaternion.SlerpUnclamped(previousRotation, rotation, (float)interpolationFactor);
                    }
                    else
                    {
                        transform.position = position;
                        transform.rotation = rotation;
                    }
                    mustUpdateTransform = false;
                }
                pos = transform.position.ToBullet();
                rot = transform.rotation.ToBullet();
            }
        }
Exemplo n.º 2
0
 public BGameObjectMotionState(Transform transform)
 {
     this.transform = transform;
     pos            = transform.position.ToBullet();
     rot            = transform.rotation.ToBullet();
     threadHelper   = BPhysicsWorld.Get().PhysicsWorldHelper as BThreadedWorldHelper;
 }
 //Bullet wants me to fill in worldTrans
 //This is called by bullet once when rigid body is added to the the world
 //For kinematic rigid bodies it is called every simulation step
 //[MonoPInvokeCallback(typeof(GetTransformDelegate))]
 public override void GetWorldTransform(out BM.Matrix worldTrans)
 {
     //Matrix4x4 trans = transform.localToWorldMatrix;
     //worldTrans = trans.ToBullet();
     BulletSharp.Math.Quaternion q = transform.rotation.ToBullet();
     BulletSharp.Math.Matrix.RotationQuaternion(ref q, out worldTrans);
     worldTrans.Origin = transform.position.ToBullet();
 }
    /// <summary>
    /// Slightly modified BPairCachingGhostObject's _BuildCollisionObject method, sets local variables.
    /// Done on Initialization.
    /// </summary>
    internal override bool _BuildCollisionObject()
    {
        #region Remove old collision object.
        BPhysicsWorld world = BPhysicsWorld.Get();
        if (m_collisionObject != null)
        {
            if (isInWorld && world != null)
            {
                isInWorld = false;
                world.RemoveCollisionObject(this);
            }
        }
        #endregion

        #region Warnings and Errors
        //Friendly note
        if (collisionShape.transform.localScale != UnityEngine.Vector3.one)
        {
            Debug.LogWarning("The local scale on this collision shape is not one. Bullet physics does not support scaling on a rigid body world transform. Instead alter the dimensions of the CollisionShape. " + name, this);
        }

        if (collisionShape == null)
        {
            Debug.LogError("There was no collision shape set. " + name, this);
            return(false);
        }
        if (!(collisionShape.GetCollisionShape() is ConvexShape))
        {
            Debug.LogError("The CollisionShape on this character controller is not a convex shape. " + name, this);
            return(false);
        }
        #endregion

        #region Init PairCachingGhostObject and ConvexShape
        m_collisionObject = new PairCachingGhostObject();

        m_collisionShape = collisionShape;
        m_collisionObject.CollisionShape = m_collisionShape.GetCollisionShape();
        m_collisionObject.CollisionFlags = m_collisionFlags;

        BulletSharp.Math.Matrix     worldTrans;
        BulletSharp.Math.Quaternion q = transform.rotation.ToBullet();
        BulletSharp.Math.Matrix.RotationQuaternion(ref q, out worldTrans);
        worldTrans.Origin = transform.position.ToBullet();
        m_collisionObject.WorldTransform = worldTrans;
        m_collisionObject.UserObject     = this;
        #endregion

        ghostObject = (PairCachingGhostObject)m_collisionObject;
        convexShape = (ConvexShape)m_collisionShape.GetCollisionShape();

        world.AddAction(this);

        return(true);
    }
Exemplo n.º 5
0
        public static Vector3 ToEulerAngles(this Quaternion q)
        {
            var sqw = q.W * q.W;
            var sqx = q.X * q.X;
            var sqy = q.Y * q.Y;
            var sqz = q.Z * q.Z;

            return(new Vector3(
                       (float)Math.Atan2(2f * (q.Y * q.Z + q.X * q.W), -sqx - sqy + sqz + sqw),
                       (float)-Math.Asin(2f * (q.X * q.Z - q.Y * q.W)),
                       (float)Math.Atan2(2f * (q.X * q.Y + q.Z * q.W), sqx - sqy - sqz + sqw)));
        }
        public static void SetOrientation(this Matrix bm, Quaternion q)
        {
            var xx = q.X * q.X;
            var yy = q.Y * q.Y;
            var zz = q.Z * q.Z;
            var xy = q.X * q.Y;
            var zw = q.Z * q.W;
            var zx = q.Z * q.X;
            var yw = q.Y * q.W;
            var yz = q.Y * q.Z;
            var xw = q.X * q.W;

            bm.M11 = 1.0f - (2.0f * (yy + zz));
            bm.M12 = 2.0f * (xy + zw);
            bm.M13 = 2.0f * (zx - yw);
            bm.M21 = 2.0f * (xy - zw);
            bm.M22 = 1.0f - (2.0f * (zz + xx));
            bm.M23 = 2.0f * (yz + xw);
            bm.M31 = 2.0f * (zx + yw);
            bm.M32 = 2.0f * (yz - xw);
            bm.M33 = 1.0f - (2.0f * (yy + xx));
        }
Exemplo n.º 7
0
 //Bullet wants me to fill in worldTrans
 //This is called by bullet once when rigid body is added to the the world
 //For kinematic rigid bodies it is called every simulation step
 //[MonoPInvokeCallback(typeof(GetTransformDelegate))]
 public override void GetWorldTransform(out BM.Matrix worldTrans)
 {
     BulletSharp.Math.Vector3    pos = unit.Position.ToBullet();
     BulletSharp.Math.Quaternion rot = unit.Quaternion.ToBullet();
     BulletSharp.Math.Matrix.AffineTransformation(1f, ref rot, ref pos, out worldTrans);
 }
Exemplo n.º 8
0
    //IMPORTANT Time.fixedTime must match the timestep being used here.
    public static List <UnityEngine.Vector3> SimulateBall(BRigidBody ballRb, UnityEngine.Vector3 ballThrowForce, int numberOfSimulationSteps, bool reverseOrder)
    {
        var ballPositions = new List <UnityEngine.Vector3>(numberOfSimulationSteps);

        //Create a World
        Debug.Log("Initialize physics");

        CollisionConfiguration CollisionConf;
        CollisionDispatcher    Dispatcher;
        BroadphaseInterface    Broadphase;
        CollisionWorld         cw;
        ConstraintSolver       Solver;

        BulletSharp.SoftBody.SoftBodyWorldInfo softBodyWorldInfo;

        //This should create a copy of the BPhysicsWorld with the same settings
        BPhysicsWorld bw = BPhysicsWorld.Get();

        bw.CreatePhysicsWorld(out cw, out CollisionConf, out Dispatcher, out Broadphase, out Solver, out softBodyWorldInfo);
        World = (DiscreteDynamicsWorld)cw;

        //Copy all existing rigidbodies in scene
        // IMPORTANT rigidbodies must be added to the offline world in the same order that they are in the source world
        // this is because collisions must be resolved in the same order for the sim to be deterministic
        DiscreteDynamicsWorld sourceWorld = (DiscreteDynamicsWorld)bw.world;

        BulletSharp.RigidBody   bulletBallRb = null;
        BulletSharp.Math.Matrix mm           = BulletSharp.Math.Matrix.Identity;
        for (int i = 0; i < sourceWorld.NumCollisionObjects; i++)
        {
            CollisionObject co = sourceWorld.CollisionObjectArray[i];
            if (co != null && co.UserObject is BRigidBody)
            {
                BRigidBody      rb            = (BRigidBody)co.UserObject;
                float           mass          = rb.isDynamic() ? rb.mass : 0f;
                BCollisionShape existingShape = rb.GetComponent <BCollisionShape>();
                CollisionShape  shape         = null;
                if (existingShape is BSphereShape)
                {
                    shape = ((BSphereShape)existingShape).CopyCollisionShape();
                }
                else if (existingShape is BBoxShape)
                {
                    shape = ((BBoxShape)existingShape).CopyCollisionShape();
                }

                RigidBody bulletRB = null;
                BulletSharp.Math.Vector3 localInertia = new BulletSharp.Math.Vector3();
                rb.CreateOrConfigureRigidBody(ref bulletRB, ref localInertia, shape, null);
                BulletSharp.Math.Vector3    pos = rb.GetCollisionObject().WorldTransform.Origin;
                BulletSharp.Math.Quaternion rot = rb.GetCollisionObject().WorldTransform.GetOrientation();
                BulletSharp.Math.Matrix.AffineTransformation(1f, ref rot, ref pos, out mm);
                bulletRB.WorldTransform = mm;
                World.AddRigidBody(bulletRB, rb.groupsIBelongTo, rb.collisionMask);
                if (rb == ballRb)
                {
                    bulletBallRb = bulletRB;
                    bulletRB.ApplyCentralImpulse(ballThrowForce.ToBullet());
                }
            }
        }

        //Step the simulation numberOfSimulationSteps times
        for (int i = 0; i < numberOfSimulationSteps; i++)
        {
            int numSteps = World.StepSimulation(1f / 60f, 10, 1f / 60f);
            ballPositions.Add(bulletBallRb.WorldTransform.Origin.ToUnity());
        }

        UnityEngine.Debug.Log("ExitPhysics");
        if (World != null)
        {
            //remove/dispose constraints
            int i;
            for (i = World.NumConstraints - 1; i >= 0; i--)
            {
                TypedConstraint constraint = World.GetConstraint(i);
                World.RemoveConstraint(constraint);
                constraint.Dispose();
            }

            //remove the rigidbodies from the dynamics world and delete them
            for (i = World.NumCollisionObjects - 1; i >= 0; i--)
            {
                CollisionObject obj  = World.CollisionObjectArray[i];
                RigidBody       body = obj as RigidBody;
                if (body != null && body.MotionState != null)
                {
                    body.MotionState.Dispose();
                }
                World.RemoveCollisionObject(obj);
                obj.Dispose();
            }

            World.Dispose();
            Broadphase.Dispose();
            Dispatcher.Dispose();
            CollisionConf.Dispose();
        }

        if (Broadphase != null)
        {
            Broadphase.Dispose();
        }
        if (Dispatcher != null)
        {
            Dispatcher.Dispose();
        }
        if (CollisionConf != null)
        {
            CollisionConf.Dispose();
        }

        return(ballPositions);
    }
Exemplo n.º 9
0
        //todo(erwincoumans) Quick hack, reference to InvertedPendulumPDControl implementation. Will create a separate header/source file for this.
        public static MultiBody createInvertedPendulumMultiBody(float radius, MultiBodyDynamicsWorld world, Matrix baseWorldTrans, bool fixedBase)
        {
            BulletSharp.Math.Vector4[] colors = new BulletSharp.Math.Vector4[]
            {
                new BulletSharp.Math.Vector4(1, 0, 0, 1),
                new BulletSharp.Math.Vector4(0, 1, 0, 1),
                new BulletSharp.Math.Vector4(0, 1, 1, 1),
                new BulletSharp.Math.Vector4(1, 1, 0, 1),
            };
            int curColor = 0;

            bool damping     = false;
            bool gyro        = false;
            int  numLinks    = 2;
            bool spherical   = false;               //set it ot false -to use 1DoF hinges instead of 3DoF sphericals
            bool canSleep    = false;
            bool selfCollide = false;

            BulletSharp.Math.Vector3 linkHalfExtents = new BulletSharp.Math.Vector3(0.05f, 0.37f, 0.1f);
            BulletSharp.Math.Vector3 baseHalfExtents = new BulletSharp.Math.Vector3(0.04f, 0.35f, 0.08f);


            //mbC.forceMultiDof();							//if !spherical, you can comment this line to check the 1DoF algorithm
            //init the base
            BulletSharp.Math.Vector3 baseInertiaDiag = new BulletSharp.Math.Vector3(0.0f, 0.0f, 0.0f);
            float baseMass = fixedBase ? 0.0f : 10.0f;

            if (baseMass != 0)
            {
                //CollisionShape *shape = new btSphereShape(baseHalfExtents[0]);// btBoxShape(BulletSharp.Math.Vector3(baseHalfExtents[0], baseHalfExtents[1], baseHalfExtents[2]));
                CollisionShape shape = new BoxShape(new BulletSharp.Math.Vector3(baseHalfExtents[0], baseHalfExtents[1], baseHalfExtents[2]));
                shape.CalculateLocalInertia(baseMass, out baseInertiaDiag);
                shape.Dispose();
            }


            MultiBody pMultiBody = new MultiBody(numLinks, 0, baseInertiaDiag, fixedBase, canSleep);

            pMultiBody.BaseWorldTransform = baseWorldTrans;
            BulletSharp.Math.Vector3 vel = new BulletSharp.Math.Vector3(0, 0, 0);
            //	pMultiBody.setBaseVel(vel);

            //init the links
            BulletSharp.Math.Vector3 hingeJointAxis = new BulletSharp.Math.Vector3(1, 0, 0);

            //y-axis assumed up
            BulletSharp.Math.Vector3 parentComToCurrentCom    = new BulletSharp.Math.Vector3(0, -linkHalfExtents[1] * 2.0f, 0); //par body's COM to cur body's COM offset
            BulletSharp.Math.Vector3 currentPivotToCurrentCom = new BulletSharp.Math.Vector3(0, -linkHalfExtents[1], 0);        //cur body's COM to cur body's PIV offset
            BulletSharp.Math.Vector3 parentComToCurrentPivot  = parentComToCurrentCom - currentPivotToCurrentCom;               //par body's COM to cur body's PIV offset

            //////
            float q0 = 1.0f * Mathf.PI / 180.0f;

            BulletSharp.Math.Quaternion quat0 = new BulletSharp.Math.Quaternion(new BulletSharp.Math.Vector3(1, 0, 0), q0);
            quat0.Normalize();
            /////

            for (int i = 0; i < numLinks; ++i)
            {
                float linkMass = 1.0f;
                //if (i==3 || i==2)
                //	linkMass= 1000;
                BulletSharp.Math.Vector3 linkInertiaDiag = new BulletSharp.Math.Vector3(0.0f, 0.0f, 0.0f);

                CollisionShape shape = null;
                if (i == 0)
                {
                    shape = new BoxShape(new BulletSharp.Math.Vector3(linkHalfExtents[0], linkHalfExtents[1], linkHalfExtents[2]));//
                }
                else
                {
                    shape = new SphereShape(radius);
                }
                shape.CalculateLocalInertia(linkMass, out linkInertiaDiag);
                shape.Dispose();


                if (!spherical)
                {
                    //pMultiBody.setupRevolute(i, linkMass, linkInertiaDiag, i - 1, BulletSharp.Math.Quaternion(0.f, 0.f, 0.f, 1.f), hingeJointAxis, parentComToCurrentPivot, currentPivotToCurrentCom, false);

                    if (i == 0)
                    {
                        pMultiBody.SetupRevolute(i, linkMass, linkInertiaDiag, i - 1,
                                                 new BulletSharp.Math.Quaternion(0.0f, 0.0f, 0.0f, 1.0f),
                                                 hingeJointAxis,
                                                 parentComToCurrentPivot,
                                                 currentPivotToCurrentCom, false);
                    }
                    else
                    {
                        parentComToCurrentCom    = new BulletSharp.Math.Vector3(0, -radius * 2.0f, 0); //par body's COM to cur body's COM offset
                        currentPivotToCurrentCom = new BulletSharp.Math.Vector3(0, -radius, 0);        //cur body's COM to cur body's PIV offset
                        parentComToCurrentPivot  = parentComToCurrentCom - currentPivotToCurrentCom;   //par body's COM to cur body's PIV offset


                        pMultiBody.SetupFixed(i, linkMass, linkInertiaDiag, i - 1,
                                              new BulletSharp.Math.Quaternion(0.0f, 0.0f, 0.0f, 1.0f),
                                              parentComToCurrentPivot,
                                              currentPivotToCurrentCom);
                    }
                }
                else
                {
                    //pMultiBody.setupPlanar(i, linkMass, linkInertiaDiag, i - 1, BulletSharp.Math.Quaternion(0.f, 0.f, 0.f, 1.f)/*quat0*/, BulletSharp.Math.Vector3(1, 0, 0), parentComToCurrentPivot*2, false);
                    pMultiBody.SetupSpherical(i, linkMass, linkInertiaDiag, i - 1, new BulletSharp.Math.Quaternion(0.0f, 0.0f, 0.0f, 1.0f), parentComToCurrentPivot, currentPivotToCurrentCom, false);
                }
            }

            pMultiBody.FinalizeMultiDof();
            world.AddMultiBody(pMultiBody);
            MultiBody mbC = pMultiBody;

            mbC.CanSleep         = (canSleep);
            mbC.HasSelfCollision = (selfCollide);
            mbC.UseGyroTerm      = (gyro);
            //
            if (!damping)
            {
                mbC.LinearDamping  = (0.0f);
                mbC.AngularDamping = (0.0f);
            }
            else
            {
                mbC.LinearDamping  = (0.1f);
                mbC.AngularDamping = (0.9f);
            }


            if (numLinks > 0)
            {
                q0 = 180.0f * Mathf.PI / 180.0f;
                if (!spherical)
                {
                    mbC.SetJointPosMultiDof(0, new float[] { q0 });
                }
                else
                {
                    BulletSharp.Math.Vector3 vv = new BulletSharp.Math.Vector3(1, 1, 0);
                    vv.Normalize();
                    quat0 = new BulletSharp.Math.Quaternion(vv, q0);
                    quat0.Normalize();
                    float[] quat0fs = new float[] { quat0.X, quat0.Y, quat0.Z, quat0.W };
                    mbC.SetJointPosMultiDof(0, quat0fs);
                }
            }
            ///
            BulletSharp.Math.Quaternion[] world_to_local; //btAlignedObjectArray<BulletSharp.Math.Quaternion>
            world_to_local = new BulletSharp.Math.Quaternion[pMultiBody.NumLinks + 1];

            BulletSharp.Math.Vector3[] local_origin; //btAlignedObjectArray<BulletSharp.Math.Vector3>
            local_origin      = new BulletSharp.Math.Vector3[pMultiBody.NumLinks + 1];
            world_to_local[0] = pMultiBody.WorldToBaseRot;
            local_origin[0]   = pMultiBody.BasePosition;
            //  double friction = 1;
            {
                if (true)
                {
                    CollisionShape shape = new BoxShape(new BulletSharp.Math.Vector3(baseHalfExtents[0], baseHalfExtents[1], baseHalfExtents[2])); //new btSphereShape(baseHalfExtents[0]);
                                                                                                                                                   // guiHelper.createCollisionShapeGraphicsObject(shape);

                    MultiBodyLinkCollider col = new MultiBodyLinkCollider(pMultiBody, -1);
                    col.CollisionShape = shape;

                    Matrix tr = new Matrix();
                    tr.ScaleVector = BulletSharp.Math.Vector3.One;
                    //if we don't set the initial pose of the btCollisionObject, the simulator will do this
                    //when syncing the btMultiBody link transforms to the btMultiBodyLinkCollider

                    tr.Origin = local_origin[0];
                    BulletSharp.Math.Quaternion orn = new BulletSharp.Math.Quaternion(new BulletSharp.Math.Vector3(0, 0, 1), 0.25f * 3.1415926538f);

                    tr.Rotation        = (orn);
                    col.WorldTransform = (tr);

                    bool isDynamic = (baseMass > 0 && !fixedBase);
                    CollisionFilterGroups collisionFilterGroup = isDynamic ? CollisionFilterGroups.DefaultFilter : CollisionFilterGroups.StaticFilter;
                    CollisionFilterGroups collisionFilterMask  = isDynamic ? CollisionFilterGroups.AllFilter : CollisionFilterGroups.AllFilter ^ CollisionFilterGroups.StaticFilter;


                    world.AddCollisionObject(col, collisionFilterGroup, collisionFilterMask);//, 2,1+2);

                    BulletSharp.Math.Vector4 color = new BulletSharp.Math.Vector4(0.0f, 0.0f, 0.5f, 1f);
                    //guiHelper.createCollisionObjectGraphicsObject(col, color);

                    //                col.setFriction(friction);
                    pMultiBody.BaseCollider = (col);
                }
            }


            for (int i = 0; i < pMultiBody.NumLinks; ++i)
            {
                int parent = pMultiBody.GetParent(i);
                world_to_local[i + 1] = pMultiBody.GetParentToLocalRot(i) * world_to_local[parent + 1];
                BulletSharp.Math.Vector3 vv = world_to_local[i + 1].Inverse.Rotate(pMultiBody.GetRVector(i));
                local_origin[i + 1] = local_origin[parent + 1] + vv;
            }


            for (int i = 0; i < pMultiBody.NumLinks; ++i)
            {
                BulletSharp.Math.Vector3 posr = local_origin[i + 1];
                //	float pos[4]={posr.x(),posr.y(),posr.z(),1};

                float[]        quat  = new float[] { -world_to_local[i + 1].X, -world_to_local[i + 1].Y, -world_to_local[i + 1].Z, world_to_local[i + 1].W };
                CollisionShape shape = null;

                if (i == 0)
                {
                    shape = new BoxShape(new BulletSharp.Math.Vector3(linkHalfExtents[0], linkHalfExtents[1], linkHalfExtents[2]));//btSphereShape(linkHalfExtents[0]);
                }
                else
                {
                    shape = new SphereShape(radius);
                }

                //guiHelper.createCollisionShapeGraphicsObject(shape);
                MultiBodyLinkCollider col = new MultiBodyLinkCollider(pMultiBody, i);
                col.CollisionShape = (shape);
                Matrix tr = new Matrix();
                tr.ScaleVector     = new BulletSharp.Math.Vector3();
                tr.Origin          = (posr);
                tr.Rotation        = (new BulletSharp.Math.Quaternion(quat[0], quat[1], quat[2], quat[3]));
                col.WorldTransform = (tr);
                //       col.setFriction(friction);
                bool isDynamic = true;//(linkMass > 0);
                CollisionFilterGroups collisionFilterGroup = isDynamic ? CollisionFilterGroups.DefaultFilter : CollisionFilterGroups.StaticFilter;
                CollisionFilterGroups collisionFilterMask  = isDynamic ? CollisionFilterGroups.AllFilter : CollisionFilterGroups.AllFilter ^ CollisionFilterGroups.StaticFilter;

                //if (i==0||i>numLinks-2)
                {
                    world.AddCollisionObject(col, collisionFilterGroup, collisionFilterMask);//,2,1+2);
                    BulletSharp.Math.Vector4 color = colors[curColor];
                    curColor++;
                    curColor &= 3;
                    //guiHelper.createCollisionObjectGraphicsObject(col, color);


                    pMultiBody.GetLink(i).Collider = col;
                }
            }

            return(pMultiBody);
        }
Exemplo n.º 10
0
        //convert from Bullet

        public static Quaternion Convert(BulletSharp.Math.Quaternion v)
        {
            return(new Quaternion(v.X, v.Y, v.Z, v.W));
        }
Exemplo n.º 11
0
        public void ConvertURDF2BulletInternal(
            URDFImporterInterface u2b,
            MultiBodyCreationInterface creation,
            URDF2BulletCachedData cache, int urdfLinkIndex,
            Matrix parentTransformInWorldSpace,
            GameObject parentGameObject,
            MultiBodyDynamicsWorld world1,
            bool createMultiBody, string pathPrefix,
            bool enableConstraints,
            ConvertURDFFlags flags = 0)
        {
            Matrix    linkTransformInWorldSpace = Matrix.Identity;
            int       mbLinkIndex     = cache.getMbIndexFromUrdfIndex(urdfLinkIndex);
            int       urdfParentIndex = cache.getParentUrdfIndex(urdfLinkIndex);
            int       mbParentIndex   = cache.getMbIndexFromUrdfIndex(urdfParentIndex);
            RigidBody parentRigidBody = null;

            //b3Printf();
            if (debugLevel >= BDebug.DebugType.Debug)
            {
                Debug.LogFormat("mb link index = {0}\n", mbLinkIndex);
            }

            Matrix parentLocalInertialFrame = Matrix.Identity;
            float  parentMass = (1);

            BulletSharp.Math.Vector3 parentLocalInertiaDiagonal = new BulletSharp.Math.Vector3(1, 1, 1);

            if (urdfParentIndex == -2)
            {
                if (debugLevel >= BDebug.DebugType.Debug)
                {
                    Debug.LogFormat("root link has no parent\n");
                }
            }
            else
            {
                if (debugLevel >= BDebug.DebugType.Debug)
                {
                    Debug.LogFormat("urdf parent index = {0}", urdfParentIndex);
                    Debug.LogFormat("mb parent index = {0}", mbParentIndex);
                }
                parentRigidBody = cache.getRigidBodyFromLink(urdfParentIndex);
                u2b.getMassAndInertia(urdfParentIndex, out parentMass, out parentLocalInertiaDiagonal, out parentLocalInertialFrame);
            }

            float  mass = 0;
            Matrix localInertialFrame = Matrix.Identity;

            BulletSharp.Math.Vector3 localInertiaDiagonal = new BulletSharp.Math.Vector3(0, 0, 0);
            u2b.getMassAndInertia(urdfLinkIndex, out mass, out localInertiaDiagonal, out localInertialFrame);
            Matrix parent2joint = Matrix.Identity;

            UrdfJointTypes jointType;

            BulletSharp.Math.Vector3 jointAxisInJointSpace;
            float jointLowerLimit;
            float jointUpperLimit;
            float jointDamping;
            float jointFriction;
            float jointMaxForce;
            float jointMaxVelocity;

            bool   hasParentJoint = u2b.getJointInfo2(urdfLinkIndex, out parent2joint, out linkTransformInWorldSpace, out jointAxisInJointSpace, out jointType, out jointLowerLimit, out jointUpperLimit, out jointDamping, out jointFriction, out jointMaxForce, out jointMaxVelocity);
            string linkName       = u2b.getLinkName(urdfLinkIndex);

            if ((flags & ConvertURDFFlags.CUF_USE_SDF) != 0)
            {
                Matrix tmp = new Matrix();
                Matrix.Invert(ref parentTransformInWorldSpace, out tmp);
                Matrix.Multiply(ref tmp, ref linkTransformInWorldSpace, out parent2joint);
            }
            else
            {
                if ((flags & ConvertURDFFlags.CUF_USE_MJCF) != 0)
                {
                    linkTransformInWorldSpace = parentTransformInWorldSpace * linkTransformInWorldSpace;
                }
                else
                {
                    linkTransformInWorldSpace = parentTransformInWorldSpace * parent2joint;
                }
            }

            GameObject gameObject = new GameObject(linkName);

            if (parentGameObject != null)
            {
                gameObject.transform.parent = parentGameObject.transform;
            }
            //--------------------

            /*
             * bool hasParentJoint = loader.getJointInfo2(linkIndex, out parent2joint, out linkTransformInWorldSpace, out jointAxisInJointSpace, out jointType, out jointLowerLimit, out jointUpperLimit, out jointDamping, out jointFriction, out jointMaxForce, out jointMaxVelocity);
             * string linkName = loader.getLinkName(linkIndex);
             *
             * if ((flags & ConvertURDFFlags.CUF_USE_SDF) != 0)
             * {
             *  Matrix tmp = parentTransformInWorldSpace.Inverse();
             *  Matrix.Multiply(ref tmp, ref linkTransformInWorldSpace, out parent2joint);
             * }
             * else
             * {
             *  if ((flags & ConvertURDFFlags.CUF_USE_MJCF) != 0)
             *  {
             *      linkTransformInWorldSpace = parentTransformInWorldSpace * linkTransformInWorldSpace;
             *  }
             *  else
             *  {
             *      linkTransformInWorldSpace = parentTransformInWorldSpace * parent2joint;
             *  }
             * }
             *
             * lgo.transform.position = linkTransformInWorldSpace.Origin.ToUnity();
             */
            //--------------------
            gameObject.transform.position = linkTransformInWorldSpace.Origin.ToUnity();
            gameObject.transform.rotation = linkTransformInWorldSpace.Rotation.ToUnity();

            BCollisionShape compoundShape = u2b.convertLinkCollisionShapes(urdfLinkIndex, pathPrefix, ref localInertialFrame, gameObject);


            int graphicsIndex;

            {
                graphicsIndex = u2b.convertLinkVisualShapes(urdfLinkIndex, pathPrefix, ref localInertialFrame);
            }

            if (compoundShape != null)
            {
                UrdfMaterialColor matColor;
                Color             color2   = Color.red;
                Color             specular = new Color(0.5f, 0.5f, 0.5f);
                if (u2b.getLinkColor2(urdfLinkIndex, out matColor))
                {
                    color2   = matColor.m_rgbaColor;
                    specular = matColor.m_specularColor;
                }

                if (mass != 0)
                {
                    if ((flags & ConvertURDFFlags.CUF_USE_URDF_INERTIA) == 0)
                    {
                        compoundShape.GetCollisionShape().CalculateLocalInertia(mass, out localInertiaDiagonal);
                        Debug.Assert(localInertiaDiagonal[0] < 1e10);
                        Debug.Assert(localInertiaDiagonal[1] < 1e10);
                        Debug.Assert(localInertiaDiagonal[2] < 1e10);
                    }
                    URDFLinkContactInfo contactInfo;
                    u2b.getLinkContactInfo(urdfLinkIndex, out contactInfo);
                    //temporary inertia scaling until we load inertia from URDF
                    if ((contactInfo.m_flags & URDF_LinkContactFlags.URDF_CONTACT_HAS_INERTIA_SCALING) != 0)
                    {
                        localInertiaDiagonal *= contactInfo.m_inertiaScaling;
                    }
                }

                RigidBody linkRigidBody             = null;
                Matrix    inertialFrameInWorldSpace = linkTransformInWorldSpace * localInertialFrame;

                if (!createMultiBody)
                {
                    RigidBody body = creation.allocateRigidBody(urdfLinkIndex, mass, localInertiaDiagonal, inertialFrameInWorldSpace, compoundShape.GetCollisionShape());
                    linkRigidBody = body;
                    world1.AddRigidBody(body);
                    compoundShape.GetCollisionShape().UserIndex = (graphicsIndex);
                    URDFLinkContactInfo contactInfo;
                    u2b.getLinkContactInfo(urdfLinkIndex, out contactInfo);
                    ProcessContactParameters(contactInfo, body);
                    creation.createRigidBodyGraphicsInstance2(urdfLinkIndex, body, color2, specular, graphicsIndex);
                    cache.registerRigidBody(urdfLinkIndex, body, inertialFrameInWorldSpace, mass, localInertiaDiagonal, compoundShape.GetCollisionShape(), ref localInertialFrame);
                    //untested: u2b.convertLinkVisualShapes2(linkIndex,urdfLinkIndex,pathPrefix,localInertialFrame,body);
                }
                else
                {
                    if (cache.m_bulletMultiBody == null)
                    {
                        // creating base
                        bool canSleep       = false;
                        bool isFixedBase    = (mass == 0);//todo: figure out when base is fixed
                        int  totalNumJoints = cache.m_totalNumJoints1;
                        //cache.m_bulletMultiBody = creation.allocateMultiBody(urdfLinkIndex, totalNumJoints, mass, localInertiaDiagonal, isFixedBase, canSleep);
                        BMultiBody bmm = cache.m_bulletMultiBody = gameObject.AddComponent <BMultiBody>();
                        bmm.fixedBase = isFixedBase;
                        bmm.canSleep  = canSleep;
                        bmm.baseMass  = mass;
                        //new btMultiBody(totalNumJoints, mass, localInertiaDiagonal, isFixedBase, canSleep);
                        //if ((flags & ConvertURDFFlags.CUF_USE_MJCF) != 0)
                        //{
                        //    cache.m_bulletMultiBody.BaseWorldTransform = (linkTransformInWorldSpace);
                        //}
                        //cache.registerMultiBody(urdfLinkIndex, cache.m_bulletMultiBody, inertialFrameInWorldSpace, mass, localInertiaDiagonal, compoundShape.GetCollisionShape(), ref localInertialFrame);
                    }
                }

                //create a joint if necessary
                BMultiBodyLink bmbl = null;
                if (hasParentJoint)
                {
                    //====================
                    //btTransform offsetInA, offsetInB;
                    //offsetInA = parentLocalInertialFrame.inverse() * parent2joint;
                    //offsetInB = localInertialFrame.inverse();
                    //btQuaternion parentRotToThis = offsetInB.getRotation() * offsetInA.inverse().getRotation();
                    //=====================
                    Matrix offsetInA = new Matrix(), offsetInB = new Matrix();
                    Matrix.Invert(ref parentLocalInertialFrame, out offsetInA);
                    offsetInA = offsetInA * parent2joint;
                    Matrix.Invert(ref localInertialFrame, out offsetInB);
                    Matrix offsetInAInv = new Matrix();
                    Matrix.Invert(ref offsetInA, out offsetInAInv);
                    BulletSharp.Math.Quaternion parentRotToThis = offsetInB.GetRotation() * offsetInAInv.GetRotation();

                    Matrix tmp = new Matrix();
                    Matrix.Invert(ref parentTransformInWorldSpace, out tmp);
                    Matrix tmp2 = new Matrix();
                    Matrix.Invert(ref parent2joint, out tmp2);
                    Matrix tmp3       = new Matrix();
                    Matrix tmp4       = linkTransformInWorldSpace;
                    Matrix link2joint = new Matrix();
                    Matrix.Multiply(ref tmp, ref tmp2, out tmp3);
                    Matrix.Multiply(ref tmp3, ref tmp4, out link2joint);

                    if (debugLevel >= BDebug.DebugType.Debug)
                    {
                        Matrix linkTransformInWorldSpaceInv = new Matrix(), parentTransformInWorldSpaceInv = new Matrix();
                        Matrix.Invert(ref linkTransformInWorldSpace, out linkTransformInWorldSpaceInv);
                        Matrix.Invert(ref parentTransformInWorldSpace, out parentTransformInWorldSpaceInv);
                        Debug.Log("Creating link " + linkName + " offsetInA=" + offsetInA.Origin + " offsetInB=" + offsetInB.Origin + " parentLocalInertialFrame=" + parentLocalInertialFrame.Origin + " localInertialFrame=" + localInertialFrame.Origin + " localTrnaform=" +
                                  " linkTransInWorldSpace=" + linkTransformInWorldSpace.Origin +
                                  " linkTransInWorldSpaceInv=" + linkTransformInWorldSpaceInv.Origin +
                                  " parentTransInWorldSpace=" + parentTransformInWorldSpace.Origin +
                                  " parentTransInWorldSpaceInv=" + parentTransformInWorldSpaceInv.Origin +
                                  " link2joint=" + link2joint.Origin +
                                  " jointType=" + jointType);
                    }

                    bool disableParentCollision = true;

                    switch (jointType)
                    {
                    case UrdfJointTypes.URDFFloatingJoint:
                    case UrdfJointTypes.URDFPlanarJoint:
                    case UrdfJointTypes.URDFFixedJoint:
                    {
                        if ((jointType == UrdfJointTypes.URDFFloatingJoint) || (jointType == UrdfJointTypes.URDFPlanarJoint))
                        {
                            Debug.Log("Warning: joint unsupported, creating a fixed joint instead.");
                        }
                        //creation.addLinkMapping(urdfLinkIndex, mbLinkIndex);

                        if (createMultiBody)
                        {
                            //todo: adjust the center of mass transform and pivot axis properly

                            /*
                             * cache.m_bulletMultiBody.SetupFixed(mbLinkIndex, mass, localInertiaDiagonal, mbParentIndex,
                             *                                  parentRotToThis, offsetInA.Origin, -offsetInB.Origin);
                             */
                            bmbl                    = gameObject.AddComponent <BMultiBodyLink>();
                            bmbl.jointType          = FeatherstoneJointType.Fixed;
                            bmbl.mass               = mass;
                            bmbl.localPivotPosition = offsetInB.Origin.ToUnity();
                        }
                        else
                        {
                            //b3Printf("Fixed joint\n");
                            Debug.LogError("TODO Setup 6dof ");

                            /*
                             * Generic6DofSpring2Constraint dof6 = null;
                             *
                             * //backward compatibility
                             * if ((flags & ConvertURDFFlags.CUF_RESERVED) != 0)
                             * {
                             *  dof6 = creation.createFixedJoint(urdfLinkIndex, parentRigidBody, linkRigidBody, offsetInA, offsetInB);
                             * }
                             * else
                             * {
                             *  dof6 = creation.createFixedJoint(urdfLinkIndex, linkRigidBody, parentRigidBody, offsetInB, offsetInA);
                             * }
                             * if (enableConstraints)
                             *  world1.AddConstraint(dof6, true);
                             */
                        }
                        break;
                    }

                    case UrdfJointTypes.URDFContinuousJoint:
                    case UrdfJointTypes.URDFRevoluteJoint:
                    {
                        //creation.addLinkMapping(urdfLinkIndex, mbLinkIndex);
                        if (createMultiBody)
                        {
                            //cache.m_bulletMultiBody.SetupRevolute(mbLinkIndex, mass, localInertiaDiagonal, mbParentIndex,
                            //                                          parentRotToThis, (offsetInB.GetRotation().Rotate(jointAxisInJointSpace)), offsetInA.Origin,//parent2joint.getOrigin(),
                            //                                          -offsetInB.Origin,
                            //                                          disableParentCollision);
                            bmbl                    = gameObject.AddComponent <BMultiBodyLink>();
                            bmbl.jointType          = FeatherstoneJointType.Revolute;
                            bmbl.mass               = mass;
                            bmbl.localPivotPosition = offsetInB.Origin.ToUnity();
                            bmbl.rotationAxis       = offsetInB.Rotation.Rotate(jointAxisInJointSpace).ToUnity();
                            if (jointType == UrdfJointTypes.URDFRevoluteJoint && jointLowerLimit <= jointUpperLimit)
                            {
                                //string name = u2b.getLinkName(urdfLinkIndex);
                                //printf("create btMultiBodyJointLimitConstraint for revolute link name=%s urdf link index=%d (low=%f, up=%f)\n", name.c_str(), urdfLinkIndex, jointLowerLimit, jointUpperLimit);
                                BMultiBodyJointLimitConstraint mbc = gameObject.AddComponent <BMultiBodyJointLimitConstraint>();
                                mbc.m_jointLowerLimit = jointLowerLimit;
                                mbc.m_jointUpperLimit = jointUpperLimit;
                            }

                            /*
                             * Debug.Log("=========== Creating joint for: " + gameObject.name);
                             * Debug.Log("parentRotateToThis: " + parentRotToThis.ToUnity().eulerAngles);
                             * Debug.Log("rotationAxis: " + bmbl.rotationAxis);
                             * Debug.Log("offsetInA: " + offsetInA.Origin);
                             * Debug.Log("negOffsetInB: " + -offsetInB.Origin);
                             */
                        }
                        else
                        {
                            Generic6DofSpring2Constraint dof6 = null;
                            //backwards compatibility
                            if ((flags & ConvertURDFFlags.CUF_RESERVED) != 0)
                            {
                                dof6 = creation.createRevoluteJoint(urdfLinkIndex, parentRigidBody, linkRigidBody, offsetInA, offsetInB, jointAxisInJointSpace, jointLowerLimit, jointUpperLimit);
                            }
                            else
                            {
                                dof6 = creation.createRevoluteJoint(urdfLinkIndex, linkRigidBody, parentRigidBody, offsetInB, offsetInA, jointAxisInJointSpace, jointLowerLimit, jointUpperLimit);
                            }
                            if (enableConstraints)
                            {
                                world1.AddConstraint(dof6, true);
                            }
                            //b3Printf("Revolute/Continuous joint\n");
                        }

                        break;
                    }

                    case UrdfJointTypes.URDFPrismaticJoint:
                    {
                        //creation.addLinkMapping(urdfLinkIndex, mbLinkIndex);

                        if (createMultiBody)
                        {
                            //cache.m_bulletMultiBody.SetupPrismatic(mbLinkIndex, mass, localInertiaDiagonal, mbParentIndex,
                            //                                           parentRotToThis, (offsetInB.GetRotation().Rotate(jointAxisInJointSpace)), offsetInA.Origin,//parent2joint.getOrigin(),
                            //                                           -offsetInB.Origin,
                            //                                           disableParentCollision);
                            bmbl                    = gameObject.AddComponent <BMultiBodyLink>();
                            bmbl.jointType          = FeatherstoneJointType.Prismatic;
                            bmbl.mass               = mass;
                            bmbl.localPivotPosition = offsetInB.Origin.ToUnity();
                            bmbl.rotationAxis       = offsetInB.Rotation.Rotate(jointAxisInJointSpace).ToUnity();

                            if (jointLowerLimit <= jointUpperLimit)
                            {
                                //string name = u2b.getLinkName(urdfLinkIndex);
                                //printf("create btMultiBodyJointLimitConstraint for prismatic link name=%s urdf link index=%d (low=%f, up=%f)\n", name.c_str(), urdfLinkIndex, jointLowerLimit,jointUpperLimit);
                                BMultiBodyJointLimitConstraint mbc = gameObject.AddComponent <BMultiBodyJointLimitConstraint>();
                                mbc.m_jointLowerLimit = jointLowerLimit;
                                mbc.m_jointUpperLimit = jointUpperLimit;
                            }
                            //printf("joint lower limit=%d, upper limit = %f\n", jointLowerLimit, jointUpperLimit);
                        }
                        else
                        {
                            Generic6DofSpring2Constraint dof6 = creation.createPrismaticJoint(urdfLinkIndex, parentRigidBody, linkRigidBody, offsetInA, offsetInB, jointAxisInJointSpace, jointLowerLimit, jointUpperLimit);

                            if (enableConstraints)
                            {
                                world1.AddConstraint(dof6, true);
                            }

                            //b3Printf("Prismatic\n");
                        }

                        break;
                    }

                    default:
                    {
                        //b3Printf("Error: unsupported joint type in URDF (%d)\n", jointType);
                        Debug.Assert(false);
                        break;
                    }
                    }
                }

                if (createMultiBody)
                {
                    if (bmbl != null)
                    {
                        bmbl.jointDamping  = jointDamping;
                        bmbl.jointFriction = jointFriction;
                        //bmbl.jointLowerLimit = jointLowerLimit;
                        //bmbl.jointUpperLimit = jointUpperLimit;
                        //bmbl.jointMaxForce = jointMaxForce;
                        //bmbl.jointMaxVelocity = jointMaxVelocity;
                    }
                    {
                        /*
                         * MultiBodyLinkCollider col = creation.allocateMultiBodyLinkCollider(urdfLinkIndex, mbLinkIndex, cache.m_bulletMultiBody);
                         *
                         * compoundShape.GetCollisionShape().UserIndex = (graphicsIndex);
                         *
                         * col.CollisionShape = (compoundShape.GetCollisionShape());
                         *
                         * Matrix tr = Matrix.Identity;
                         *
                         * tr = linkTransformInWorldSpace;
                         * //if we don't set the initial pose of the btCollisionObject, the simulator will do this
                         * //when syncing the btMultiBody link transforms to the btMultiBodyLinkCollider
                         *
                         * col.WorldTransform = (tr);
                         *
                         * //base and fixed? . static, otherwise flag as dynamic
                         * bool isDynamic = (mbLinkIndex < 0 && cache.m_bulletMultiBody.HasFixedBase) ? false : true;
                         * CollisionFilterGroups collisionFilterGroup = isDynamic ? (CollisionFilterGroups.DefaultFilter) : (CollisionFilterGroups.StaticFilter);
                         * CollisionFilterGroups collisionFilterMask = isDynamic ? (CollisionFilterGroups.AllFilter) : (CollisionFilterGroups.AllFilter ^ CollisionFilterGroups.StaticFilter);
                         *
                         * CollisionFilterGroups colGroup = 0, colMask = 0;
                         * UrdfCollisionFlags collisionFlags = u2b.getCollisionGroupAndMask(urdfLinkIndex, out colGroup, out colMask);
                         * if ((collisionFlags & UrdfCollisionFlags.URDF_HAS_COLLISION_GROUP) != 0)
                         * {
                         *  collisionFilterGroup = colGroup;
                         * }
                         * if ((collisionFlags & UrdfCollisionFlags.URDF_HAS_COLLISION_MASK) != 0)
                         * {
                         *  collisionFilterMask = colMask;
                         * }
                         * world1.AddCollisionObject(col, collisionFilterGroup, collisionFilterMask);
                         *
                         * color2 = Color.red;//(0.0,0.0,0.5);
                         * Color specularColor = new Color(1, 1, 1);
                         * UrdfMaterialColor matCol;
                         * if (u2b.getLinkColor2(urdfLinkIndex, out matCol))
                         * {
                         *  color2 = matCol.m_rgbaColor;
                         *  specularColor = matCol.m_specularColor;
                         * }
                         * {
                         *
                         *
                         *  creation.createCollisionObjectGraphicsInstance2(urdfLinkIndex, col, color2, specularColor);
                         * }
                         * {
                         *
                         *
                         *  u2b.convertLinkVisualShapes2(mbLinkIndex, urdfLinkIndex, pathPrefix, ref localInertialFrame, col, u2b.getBodyUniqueId());
                         * }
                         * URDFLinkContactInfo contactInfo;
                         * u2b.getLinkContactInfo(urdfLinkIndex, out contactInfo);
                         *
                         *
                         * ProcessContactParameters(contactInfo, col);
                         *
                         * if (mbLinkIndex >= 0) //???? double-check +/- 1
                         * {
                         *  cache.m_bulletMultiBody.GetLink(mbLinkIndex).Collider = col;
                         *  if ((flags & ConvertURDFFlags.CUF_USE_SELF_COLLISION_EXCLUDE_PARENT) != 0)
                         *  {
                         *      cache.m_bulletMultiBody.GetLink(mbLinkIndex).Flags |= (int)btMultiBodyLinkFlags.BT_MULTIBODYLINKFLAGS_DISABLE_PARENT_COLLISION;
                         *  }
                         *  if ((flags & ConvertURDFFlags.CUF_USE_SELF_COLLISION_EXCLUDE_ALL_PARENTS) != 0)
                         *  {
                         *      cache.m_bulletMultiBody.GetLink(mbLinkIndex).Flags |= (int)btMultiBodyLinkFlags.BT_MULTIBODYLINKFLAGS_DISABLE_ALL_PARENT_COLLISION;
                         *  }
                         * }
                         * else
                         * {
                         *  cache.m_bulletMultiBody.BaseCollider = (col);
                         * }
                         */
                    }
                }
                else
                {
                    //u2b.convertLinkVisualShapes2(urdfLinkIndex,urdfIndex,pathPrefix,localInertialFrame,compoundShape);
                }
            }


            List <int> urdfChildIndices = new List <int>();

            u2b.getLinkChildIndices(urdfLinkIndex, urdfChildIndices);

            int numChildren = urdfChildIndices.Count;

            for (int i = 0; i < numChildren; i++)
            {
                int urdfChildLinkIndex = urdfChildIndices[i];

                ConvertURDF2BulletInternal(u2b, creation, cache, urdfChildLinkIndex, linkTransformInWorldSpace, gameObject, world1, createMultiBody, pathPrefix, enableConstraints, flags);
            }
        }
        /// <summary>
        /// Get Quaternion rotation from BulletSharp Matrix4x4
        /// </summary>
        /// <param name="bMatrix4x4">Matrix from which to extract a rotatio</param>
        /// <returns></returns>
        public static Quaternion GetOrientation(this Matrix bMatrix4x4)
        {
            //Scaling is the length of the rows.
            Vector3 scale;

            scale.X = (float)Math.Sqrt((bMatrix4x4.M11 * bMatrix4x4.M11) + (bMatrix4x4.M12 * bMatrix4x4.M12) + (bMatrix4x4.M13 * bMatrix4x4.M13));
            scale.Y = (float)Math.Sqrt((bMatrix4x4.M21 * bMatrix4x4.M21) + (bMatrix4x4.M22 * bMatrix4x4.M22) + (bMatrix4x4.M23 * bMatrix4x4.M23));
            scale.Z = (float)Math.Sqrt((bMatrix4x4.M31 * bMatrix4x4.M31) + (bMatrix4x4.M32 * bMatrix4x4.M32) + (bMatrix4x4.M33 * bMatrix4x4.M33));

            //Divide out scaling to get rotation
            var mm11 = bMatrix4x4.M11 / scale.X;
            var mm12 = bMatrix4x4.M12 / scale.X;
            var mm13 = bMatrix4x4.M13 / scale.X;

            var mm21 = bMatrix4x4.M21 / scale.Y;
            var mm22 = bMatrix4x4.M22 / scale.Y;
            var mm23 = bMatrix4x4.M23 / scale.Y;

            var mm31 = bMatrix4x4.M31 / scale.Z;
            var mm32 = bMatrix4x4.M32 / scale.Z;
            var mm33 = bMatrix4x4.M33 / scale.Z;


            float sqrt;
            float half;
            var   trace  = mm11 + mm22 + mm33;
            var   result = new Quaternion();

            if (trace > 0.0f)
            {
                sqrt     = Mathf.Sqrt(trace + 1.0f);
                result.W = sqrt * 0.5f;
                sqrt     = 0.5f / sqrt;

                result.X = (mm23 - mm32) * sqrt;
                result.Y = (mm31 - mm13) * sqrt;
                result.Z = (mm12 - mm21) * sqrt;
            }
            else if ((mm11 >= mm22) && (mm11 >= mm33))
            {
                sqrt = Mathf.Sqrt(1.0f + mm11 - mm22 - mm33);
                half = 0.5f / sqrt;

                result.X = 0.5f * sqrt;
                result.Y = (mm12 + mm21) * half;
                result.Z = (mm13 + mm31) * half;
                result.W = (mm23 - mm32) * half;
            }
            else if (mm22 > mm33)
            {
                sqrt = Mathf.Sqrt(1.0f + mm22 - mm11 - mm33);
                half = 0.5f / sqrt;

                result.X = (mm21 + mm12) * half;
                result.Y = 0.5f * sqrt;
                result.Z = (mm32 + mm23) * half;
                result.W = (mm31 - mm13) * half;
            }
            else
            {
                sqrt = Mathf.Sqrt(1.0f + mm33 - mm11 - mm22);
                half = 0.5f / sqrt;

                result.X = (mm31 + mm13) * half;
                result.Y = (mm32 + mm23) * half;
                result.Z = 0.5f * sqrt;
                result.W = (mm12 - mm21) * half;
            }
            return(result);
        }
 /// <summary>
 /// Convert a BulletSharp Quaternion to Unity
 /// </summary>
 /// <param name="q">Quaternion to be converted</param>
 /// <returns></returns>
 public static UnityEngine.Quaternion ToUnity(this Quaternion q)
 {
     return(new UnityEngine.Quaternion(q.X, q.Y, q.Z, q.W));
 }