btSoftBody.h

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/*
Bullet Continuous Collision Detection and Physics Library
Copyright (c) 2003-2006 Erwin Coumans  https://bulletphysics.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 _BT_SOFT_BODY_H
#define _BT_SOFT_BODY_H
 
#include "LinearMath/btAlignedObjectArray.h"
#include "LinearMath/btTransform.h"
#include "LinearMath/btIDebugDraw.h"
#include "LinearMath/btVector3.h"
#include "BulletDynamics/Dynamics/btRigidBody.h"
 
#include "BulletCollision/CollisionShapes/btConcaveShape.h"
#include "BulletCollision/CollisionDispatch/btCollisionCreateFunc.h"
#include "btSparseSDF.h"
#include "BulletCollision/BroadphaseCollision/btDbvt.h"
#include "BulletDynamics/Featherstone/btMultiBodyLinkCollider.h"
#include "BulletDynamics/Featherstone/btMultiBodyConstraint.h"
//#ifdef BT_USE_DOUBLE_PRECISION
//#define btRigidBodyData       btRigidBodyDoubleData
//#define btRigidBodyDataName   "btRigidBodyDoubleData"
//#else
#define btSoftBodyData btSoftBodyFloatData
#define btSoftBodyDataName "btSoftBodyFloatData"
static const btScalar OVERLAP_REDUCTION_FACTOR = 0.1;
static unsigned long seed = 243703;
//#endif //BT_USE_DOUBLE_PRECISION
 
class btBroadphaseInterface;
class btDispatcher;
class btSoftBodySolver;
 
/* btSoftBodyWorldInfo  */
struct btSoftBodyWorldInfo
{
        btScalar air_density;
        btScalar water_density;
        btScalar water_offset;
        btScalar m_maxDisplacement;
        btVector3 water_normal;
        btBroadphaseInterface* m_broadphase;
        btDispatcher* m_dispatcher;
        btVector3 m_gravity;
        btSparseSdf<3> m_sparsesdf;
 
        btSoftBodyWorldInfo()
                : air_density((btScalar)1.2),
                  water_density(0),
                  water_offset(0),
                  m_maxDisplacement(1000.f),  //avoid soft body from 'exploding' so use some upper threshold of maximum motion that a node can travel per frame
                  water_normal(0, 0, 0),
                  m_broadphase(0),
                  m_dispatcher(0),
                  m_gravity(0, -10, 0)
        {
        }
};

class btSoftBody : public btCollisionObject
{
public:
        btAlignedObjectArray<const class btCollisionObject*> m_collisionDisabledObjects;
 
        // The solver object that handles this soft body
        btSoftBodySolver* m_softBodySolver;
 
        //
        // Enumerations
        //

        struct eAeroModel
        {
                enum _
                {
                        V_Point,             
                        V_TwoSided,          
                        V_TwoSidedLiftDrag,  
                        V_OneSided,          
                        F_TwoSided,          
                        F_TwoSidedLiftDrag,  
                        F_OneSided,          
                        END
                };
        };

        struct eVSolver
        {
                enum _
                {
                        Linear,  
                        END
                };
        };

        struct ePSolver
        {
                enum _
                {
                        Linear,     
                        Anchors,    
                        RContacts,  
                        SContacts,  
                        END
                };
        };

        struct eSolverPresets
        {
                enum _
                {
                        Positions,
                        Velocities,
                        Default = Positions,
                        END
                };
        };

        struct eFeature
        {
                enum _
                {
                        None,
                        Node,
                        Link,
                        Face,
                        Tetra,
                        END
                };
        };
 
        typedef btAlignedObjectArray<eVSolver::_> tVSolverArray;
        typedef btAlignedObjectArray<ePSolver::_> tPSolverArray;
 
        //
        // Flags
        //

        struct fCollision
        {
                enum _
                {
                        RVSmask = 0x000f,  
                        SDF_RS = 0x0001,   
                        CL_RS = 0x0002,    
                        SDF_RD = 0x0004,   
 
                        SVSmask = 0x00f0,  
                        VF_SS = 0x0010,    
                        CL_SS = 0x0020,    
                        CL_SELF = 0x0040,  
                        VF_DD = 0x0080,    
 
                        RVDFmask = 0x0f00,  
                        SDF_RDF = 0x0100,   
                        SDF_MDF = 0x0200,   
                        SDF_RDN = 0x0400,   
                        /* presets      */
                        Default = SDF_RS,
                        END
                };
        };

        struct fMaterial
        {
                enum _
                {
                        DebugDraw = 0x0001,  
                        /* presets      */
                        Default = DebugDraw,
                        END
                };
        };
 
        //
        // API Types
        //
 
        /* sRayCast             */
        struct sRayCast
        {
                btSoftBody* body;     
                eFeature::_ feature;  
                int index;            
                btScalar fraction;    
        };
 
        /* ImplicitFn   */
        struct ImplicitFn
        {
                virtual ~ImplicitFn() {}
                virtual btScalar Eval(const btVector3& x) = 0;
        };
 
        //
        // Internal types
        //
 
        typedef btAlignedObjectArray<btScalar> tScalarArray;
        typedef btAlignedObjectArray<btVector3> tVector3Array;
 
        /* sCti is Softbody contact info        */
        struct sCti
        {
                const btCollisionObject* m_colObj; /* Rigid body                               */
                btVector3 m_normal;                /* Outward normal                   */
                mutable btVector3 m_impulse;     /* Applied impulse               */
                btScalar m_offset;                 /* Offset from origin                */
                btVector3 m_bary;                  /* Barycentric weights for faces */
                sCti() : m_impulse(0, 0, 0) {}
        };
 
        /* sMedium              */
        struct sMedium
        {
                btVector3 m_velocity; /* Velocity                            */
                btScalar m_pressure;  /* Pressure                             */
                btScalar m_density;   /* Density                               */
        };
 
        /* Base type    */
        struct Element
        {
                void* m_tag;  // User data
                Element() : m_tag(0) {}
        };
        /* Material             */
        struct Material : Element
        {
                btScalar m_kLST;  // Linear stiffness coefficient [0,1]
                btScalar m_kAST;  // Area/Angular stiffness coefficient [0,1]
                btScalar m_kVST;  // Volume stiffness coefficient [0,1]
                int m_flags;      // Flags
        };
 
        /* Feature              */
        struct Feature : Element
        {
                Material* m_material;  // Material
        };
        /* Node                 */
        struct RenderNode
        {
                btVector3 m_x;
                btVector3 m_uv1;
                btVector3 m_normal;
        };
        struct Node : Feature
        {
                btVector3 m_x;       // Position
                btVector3 m_q;       // Previous step position/Test position
                btVector3 m_v;       // Velocity
                btVector3 m_vn;      // Previous step velocity
                btVector3 m_f;       // Force accumulator
                btVector3 m_n;       // Normal
                btScalar m_im;       // 1/mass
                btScalar m_area;     // Area
                btDbvtNode* m_leaf;  // Leaf data
                int m_constrained;   // depth of penetration
                int m_battach : 1;   // Attached
                int index;
                btVector3 m_splitv;               // velocity associated with split impulse
                btMatrix3x3 m_effectiveMass;      // effective mass in contact
                btMatrix3x3 m_effectiveMass_inv;  // inverse of effective mass
        };
        /* Link                 */
        ATTRIBUTE_ALIGNED16(struct)
        Link : Feature
        {
                btVector3 m_c3;      // gradient
                Node* m_n[2];        // Node pointers
                btScalar m_rl;       // Rest length
                int m_bbending : 1;  // Bending link
                btScalar m_c0;       // (ima+imb)*kLST
                btScalar m_c1;       // rl^2
                btScalar m_c2;       // |gradient|^2/c0
 
                BT_DECLARE_ALIGNED_ALLOCATOR();
        };
        struct RenderFace
        {
                RenderNode* m_n[3];  // Node pointers
        };
 
        /* Face                 */
        struct Face : Feature
        {
                Node* m_n[3];          // Node pointers
                btVector3 m_normal;    // Normal
                btScalar m_ra;         // Rest area
                btDbvtNode* m_leaf;    // Leaf data
                btVector4 m_pcontact;  // barycentric weights of the persistent contact
                btVector3 m_n0, m_n1, m_vn;
                int m_index;
        };
        /* Tetra                */
        struct Tetra : Feature
        {
                Node* m_n[4];              // Node pointers
                btScalar m_rv;             // Rest volume
                btDbvtNode* m_leaf;        // Leaf data
                btVector3 m_c0[4];         // gradients
                btScalar m_c1;             // (4*kVST)/(im0+im1+im2+im3)
                btScalar m_c2;             // m_c1/sum(|g0..3|^2)
                btMatrix3x3 m_Dm_inverse;  // rest Dm^-1
                btMatrix3x3 m_F;
                btScalar m_element_measure;
                btVector4 m_P_inv[3];  // first three columns of P_inv matrix
        };
 
        /*  TetraScratch  */
        struct TetraScratch
        {
                btMatrix3x3 m_F;           // deformation gradient F
                btScalar m_trace;          // trace of F^T * F
                btScalar m_J;              // det(F)
                btMatrix3x3 m_cofF;        // cofactor of F
                btMatrix3x3 m_corotation;  // corotatio of the tetra
        };
 
        /* RContact             */
        struct RContact
        {
                sCti m_cti;        // Contact infos
                Node* m_node;      // Owner node
                btMatrix3x3 m_c0;  // Impulse matrix
                btVector3 m_c1;    // Relative anchor
                btScalar m_c2;     // ima*dt
                btScalar m_c3;     // Friction
                btScalar m_c4;     // Hardness
 
                // jacobians and unit impulse responses for multibody
                btMultiBodyJacobianData jacobianData_normal;
                btMultiBodyJacobianData jacobianData_t1;
                btMultiBodyJacobianData jacobianData_t2;
                btVector3 t1;
                btVector3 t2;
        };
 
        class DeformableRigidContact
        {
        public:
                sCti m_cti;        // Contact infos
                btMatrix3x3 m_c0;  // Impulse matrix
                btVector3 m_c1;    // Relative anchor
                btScalar m_c2;     // inverse mass of node/face
                btScalar m_c3;     // Friction
                btScalar m_c4;     // Hardness
                btMatrix3x3 m_c5;  // inverse effective mass
 
                // jacobians and unit impulse responses for multibody
                btMultiBodyJacobianData jacobianData_normal;
                btMultiBodyJacobianData jacobianData_t1;
                btMultiBodyJacobianData jacobianData_t2;
                btVector3 t1;
                btVector3 t2;
        };
 
        class DeformableNodeRigidContact : public DeformableRigidContact
        {
        public:
                Node* m_node;  // Owner node
        };
 
        class DeformableNodeRigidAnchor : public DeformableNodeRigidContact
        {
        public:
                btVector3 m_local;  // Anchor position in body space
        };
 
        class DeformableFaceRigidContact : public DeformableRigidContact
        {
        public:
                Face* m_face;              // Owner face
                btVector3 m_contactPoint;  // Contact point
                btVector3 m_bary;          // Barycentric weights
                btVector3 m_weights;       // v_contactPoint * m_weights[i] = m_face->m_node[i]->m_v;
        };
 
        struct DeformableFaceNodeContact
        {
                Node* m_node;         // Node
                Face* m_face;         // Face
                btVector3 m_bary;     // Barycentric weights
                btVector3 m_weights;  // v_contactPoint * m_weights[i] = m_face->m_node[i]->m_v;
                btVector3 m_normal;   // Normal
                btScalar m_margin;    // Margin
                btScalar m_friction;  // Friction
                btScalar m_imf;       // inverse mass of the face at contact point
                btScalar m_c0;        // scale of the impulse matrix;
                const btCollisionObject* m_colObj;  // Collision object to collide with.
        };
 
        /* SContact             */
        struct SContact
        {
                Node* m_node;         // Node
                Face* m_face;         // Face
                btVector3 m_weights;  // Weigths
                btVector3 m_normal;   // Normal
                btScalar m_margin;    // Margin
                btScalar m_friction;  // Friction
                btScalar m_cfm[2];    // Constraint force mixing
        };
        /* Anchor               */
        struct Anchor
        {
                Node* m_node;         // Node pointer
                btVector3 m_local;    // Anchor position in body space
                btRigidBody* m_body;  // Body
                btScalar m_influence;
                btMatrix3x3 m_c0;  // Impulse matrix
                btVector3 m_c1;    // Relative anchor
                btScalar m_c2;     // ima*dt
        };
        /* Note                 */
        struct Note : Element
        {
                const char* m_text;    // Text
                btVector3 m_offset;    // Offset
                int m_rank;            // Rank
                Node* m_nodes[4];      // Nodes
                btScalar m_coords[4];  // Coordinates
        };
        /* Pose                 */
        struct Pose
        {
                bool m_bvolume;       // Is valid
                bool m_bframe;        // Is frame
                btScalar m_volume;    // Rest volume
                tVector3Array m_pos;  // Reference positions
                tScalarArray m_wgh;   // Weights
                btVector3 m_com;      // COM
                btMatrix3x3 m_rot;    // Rotation
                btMatrix3x3 m_scl;    // Scale
                btMatrix3x3 m_aqq;    // Base scaling
        };
        /* Cluster              */
        struct Cluster
        {
                tScalarArray m_masses;
                btAlignedObjectArray<Node*> m_nodes;
                tVector3Array m_framerefs;
                btTransform m_framexform;
                btScalar m_idmass;
                btScalar m_imass;
                btMatrix3x3 m_locii;
                btMatrix3x3 m_invwi;
                btVector3 m_com;
                btVector3 m_vimpulses[2];
                btVector3 m_dimpulses[2];
                int m_nvimpulses;
                int m_ndimpulses;
                btVector3 m_lv;
                btVector3 m_av;
                btDbvtNode* m_leaf;
                btScalar m_ndamping; /* Node damping          */
                btScalar m_ldamping; /* Linear damping        */
                btScalar m_adamping; /* Angular damping       */
                btScalar m_matching;
                btScalar m_maxSelfCollisionImpulse;
                btScalar m_selfCollisionImpulseFactor;
                bool m_containsAnchor;
                bool m_collide;
                int m_clusterIndex;
                Cluster() : m_leaf(0), m_ndamping(0), m_ldamping(0), m_adamping(0), m_matching(0), m_maxSelfCollisionImpulse(100.f), m_selfCollisionImpulseFactor(0.01f), m_containsAnchor(false)
                {
                }
        };
        /* Impulse              */
        struct Impulse
        {
                btVector3 m_velocity;
                btVector3 m_drift;
                int m_asVelocity : 1;
                int m_asDrift : 1;
                Impulse() : m_velocity(0, 0, 0), m_drift(0, 0, 0), m_asVelocity(0), m_asDrift(0) {}
                Impulse operator-() const
                {
                        Impulse i = *this;
                        i.m_velocity = -i.m_velocity;
                        i.m_drift = -i.m_drift;
                        return (i);
                }
                Impulse operator*(btScalar x) const
                {
                        Impulse i = *this;
                        i.m_velocity *= x;
                        i.m_drift *= x;
                        return (i);
                }
        };
        /* Body                 */
        struct Body
        {
                Cluster* m_soft;
                btRigidBody* m_rigid;
                const btCollisionObject* m_collisionObject;
 
                Body() : m_soft(0), m_rigid(0), m_collisionObject(0) {}
                Body(Cluster* p) : m_soft(p), m_rigid(0), m_collisionObject(0) {}
                Body(const btCollisionObject* colObj) : m_soft(0), m_collisionObject(colObj)
                {
                        m_rigid = (btRigidBody*)btRigidBody::upcast(m_collisionObject);
                }
 
                void activate() const
                {
                        if (m_rigid)
                                m_rigid->activate();
                        if (m_collisionObject)
                                m_collisionObject->activate();
                }
                const btMatrix3x3& invWorldInertia() const
                {
                        static const btMatrix3x3 iwi(0, 0, 0, 0, 0, 0, 0, 0, 0);
                        if (m_rigid) return (m_rigid->getInvInertiaTensorWorld());
                        if (m_soft) return (m_soft->m_invwi);
                        return (iwi);
                }
                btScalar invMass() const
                {
                        if (m_rigid) return (m_rigid->getInvMass());
                        if (m_soft) return (m_soft->m_imass);
                        return (0);
                }
                const btTransform& xform() const
                {
                        static const btTransform identity = btTransform::getIdentity();
                        if (m_collisionObject) return (m_collisionObject->getWorldTransform());
                        if (m_soft) return (m_soft->m_framexform);
                        return (identity);
                }
                btVector3 linearVelocity() const
                {
                        if (m_rigid) return (m_rigid->getLinearVelocity());
                        if (m_soft) return (m_soft->m_lv);
                        return (btVector3(0, 0, 0));
                }
                btVector3 angularVelocity(const btVector3& rpos) const
                {
                        if (m_rigid) return (btCross(m_rigid->getAngularVelocity(), rpos));
                        if (m_soft) return (btCross(m_soft->m_av, rpos));
                        return (btVector3(0, 0, 0));
                }
                btVector3 angularVelocity() const
                {
                        if (m_rigid) return (m_rigid->getAngularVelocity());
                        if (m_soft) return (m_soft->m_av);
                        return (btVector3(0, 0, 0));
                }
                btVector3 velocity(const btVector3& rpos) const
                {
                        return (linearVelocity() + angularVelocity(rpos));
                }
                void applyVImpulse(const btVector3& impulse, const btVector3& rpos) const
                {
                        if (m_rigid) m_rigid->applyImpulse(impulse, rpos);
                        if (m_soft) btSoftBody::clusterVImpulse(m_soft, rpos, impulse);
                }
                void applyDImpulse(const btVector3& impulse, const btVector3& rpos) const
                {
                        if (m_rigid) m_rigid->applyImpulse(impulse, rpos);
                        if (m_soft) btSoftBody::clusterDImpulse(m_soft, rpos, impulse);
                }
                void applyImpulse(const Impulse& impulse, const btVector3& rpos) const
                {
                        if (impulse.m_asVelocity)
                        {
                                //                              printf("impulse.m_velocity = %f,%f,%f\n",impulse.m_velocity.getX(),impulse.m_velocity.getY(),impulse.m_velocity.getZ());
                                applyVImpulse(impulse.m_velocity, rpos);
                        }
                        if (impulse.m_asDrift)
                        {
                                //                              printf("impulse.m_drift = %f,%f,%f\n",impulse.m_drift.getX(),impulse.m_drift.getY(),impulse.m_drift.getZ());
                                applyDImpulse(impulse.m_drift, rpos);
                        }
                }
                void applyVAImpulse(const btVector3& impulse) const
                {
                        if (m_rigid) m_rigid->applyTorqueImpulse(impulse);
                        if (m_soft) btSoftBody::clusterVAImpulse(m_soft, impulse);
                }
                void applyDAImpulse(const btVector3& impulse) const
                {
                        if (m_rigid) m_rigid->applyTorqueImpulse(impulse);
                        if (m_soft) btSoftBody::clusterDAImpulse(m_soft, impulse);
                }
                void applyAImpulse(const Impulse& impulse) const
                {
                        if (impulse.m_asVelocity) applyVAImpulse(impulse.m_velocity);
                        if (impulse.m_asDrift) applyDAImpulse(impulse.m_drift);
                }
                void applyDCImpulse(const btVector3& impulse) const
                {
                        if (m_rigid) m_rigid->applyCentralImpulse(impulse);
                        if (m_soft) btSoftBody::clusterDCImpulse(m_soft, impulse);
                }
        };
        /* Joint                */
        struct Joint
        {
                struct eType
                {
                        enum _
                        {
                                Linear = 0,
                                Angular,
                                Contact
                        };
                };
                struct Specs
                {
                        Specs() : erp(1), cfm(1), split(1) {}
                        btScalar erp;
                        btScalar cfm;
                        btScalar split;
                };
                Body m_bodies[2];
                btVector3 m_refs[2];
                btScalar m_cfm;
                btScalar m_erp;
                btScalar m_split;
                btVector3 m_drift;
                btVector3 m_sdrift;
                btMatrix3x3 m_massmatrix;
                bool m_delete;
                virtual ~Joint() {}
                Joint() : m_delete(false) {}
                virtual void Prepare(btScalar dt, int iterations);
                virtual void Solve(btScalar dt, btScalar sor) = 0;
                virtual void Terminate(btScalar dt) = 0;
                virtual eType::_ Type() const = 0;
        };
        /* LJoint               */
        struct LJoint : Joint
        {
                struct Specs : Joint::Specs
                {
                        btVector3 position;
                };
                btVector3 m_rpos[2];
                void Prepare(btScalar dt, int iterations);
                void Solve(btScalar dt, btScalar sor);
                void Terminate(btScalar dt);
                eType::_ Type() const { return (eType::Linear); }
        };
        /* AJoint               */
        struct AJoint : Joint
        {
                struct IControl
                {
                        virtual ~IControl() {}
                        virtual void Prepare(AJoint*) {}
                        virtual btScalar Speed(AJoint*, btScalar current) { return (current); }
                        static IControl* Default()
                        {
                                static IControl def;
                                return (&def);
                        }
                };
                struct Specs : Joint::Specs
                {
                        Specs() : icontrol(IControl::Default()) {}
                        btVector3 axis;
                        IControl* icontrol;
                };
                btVector3 m_axis[2];
                IControl* m_icontrol;
                void Prepare(btScalar dt, int iterations);
                void Solve(btScalar dt, btScalar sor);
                void Terminate(btScalar dt);
                eType::_ Type() const { return (eType::Angular); }
        };
        /* CJoint               */
        struct CJoint : Joint
        {
                int m_life;
                int m_maxlife;
                btVector3 m_rpos[2];
                btVector3 m_normal;
                btScalar m_friction;
                void Prepare(btScalar dt, int iterations);
                void Solve(btScalar dt, btScalar sor);
                void Terminate(btScalar dt);
                eType::_ Type() const { return (eType::Contact); }
        };
        /* Config               */
        struct Config
        {
                eAeroModel::_ aeromodel;    // Aerodynamic model (default: V_Point)
                btScalar kVCF;              // Velocities correction factor (Baumgarte)
                btScalar kDP;               // Damping coefficient [0,1]
                btScalar kDG;               // Drag coefficient [0,+inf]
                btScalar kLF;               // Lift coefficient [0,+inf]
                btScalar kPR;               // Pressure coefficient [-inf,+inf]
                btScalar kVC;               // Volume conversation coefficient [0,+inf]
                btScalar kDF;               // Dynamic friction coefficient [0,1]
                btScalar kMT;               // Pose matching coefficient [0,1]
                btScalar kCHR;              // Rigid contacts hardness [0,1]
                btScalar kKHR;              // Kinetic contacts hardness [0,1]
                btScalar kSHR;              // Soft contacts hardness [0,1]
                btScalar kAHR;              // Anchors hardness [0,1]
                btScalar kSRHR_CL;          // Soft vs rigid hardness [0,1] (cluster only)
                btScalar kSKHR_CL;          // Soft vs kinetic hardness [0,1] (cluster only)
                btScalar kSSHR_CL;          // Soft vs soft hardness [0,1] (cluster only)
                btScalar kSR_SPLT_CL;       // Soft vs rigid impulse split [0,1] (cluster only)
                btScalar kSK_SPLT_CL;       // Soft vs rigid impulse split [0,1] (cluster only)
                btScalar kSS_SPLT_CL;       // Soft vs rigid impulse split [0,1] (cluster only)
                btScalar maxvolume;         // Maximum volume ratio for pose
                btScalar timescale;         // Time scale
                int viterations;            // Velocities solver iterations
                int piterations;            // Positions solver iterations
                int diterations;            // Drift solver iterations
                int citerations;            // Cluster solver iterations
                int collisions;             // Collisions flags
                tVSolverArray m_vsequence;  // Velocity solvers sequence
                tPSolverArray m_psequence;  // Position solvers sequence
                tPSolverArray m_dsequence;  // Drift solvers sequence
                btScalar drag;              // deformable air drag
                btScalar m_maxStress;       // Maximum principle first Piola stress
        };
        /* SolverState  */
        struct SolverState
        {
                //if you add new variables, always initialize them!
                SolverState()
                        : sdt(0),
                          isdt(0),
                          velmrg(0),
                          radmrg(0),
                          updmrg(0)
                {
                }
                btScalar sdt;     // dt*timescale
                btScalar isdt;    // 1/sdt
                btScalar velmrg;  // velocity margin
                btScalar radmrg;  // radial margin
                btScalar updmrg;  // Update margin
        };

        struct RayFromToCaster : btDbvt::ICollide
        {
                btVector3 m_rayFrom;
                btVector3 m_rayTo;
                btVector3 m_rayNormalizedDirection;
                btScalar m_mint;
                Face* m_face;
                int m_tests;
                RayFromToCaster(const btVector3& rayFrom, const btVector3& rayTo, btScalar mxt);
                void Process(const btDbvtNode* leaf);
 
                static /*inline*/ btScalar rayFromToTriangle(const btVector3& rayFrom,
                                                                                                         const btVector3& rayTo,
                                                                                                         const btVector3& rayNormalizedDirection,
                                                                                                         const btVector3& a,
                                                                                                         const btVector3& b,
                                                                                                         const btVector3& c,
                                                                                                         btScalar maxt = SIMD_INFINITY);
        };
 
        //
        // Typedefs
        //
 
        typedef void (*psolver_t)(btSoftBody*, btScalar, btScalar);
        typedef void (*vsolver_t)(btSoftBody*, btScalar);
        typedef btAlignedObjectArray<Cluster*> tClusterArray;
        typedef btAlignedObjectArray<Note> tNoteArray;
        typedef btAlignedObjectArray<Node> tNodeArray;
        typedef btAlignedObjectArray<RenderNode> tRenderNodeArray;
        typedef btAlignedObjectArray<btDbvtNode*> tLeafArray;
        typedef btAlignedObjectArray<Link> tLinkArray;
        typedef btAlignedObjectArray<Face> tFaceArray;
        typedef btAlignedObjectArray<RenderFace> tRenderFaceArray;
        typedef btAlignedObjectArray<Tetra> tTetraArray;
        typedef btAlignedObjectArray<Anchor> tAnchorArray;
        typedef btAlignedObjectArray<RContact> tRContactArray;
        typedef btAlignedObjectArray<SContact> tSContactArray;
        typedef btAlignedObjectArray<Material*> tMaterialArray;
        typedef btAlignedObjectArray<Joint*> tJointArray;
        typedef btAlignedObjectArray<btSoftBody*> tSoftBodyArray;
        typedef btAlignedObjectArray<btAlignedObjectArray<btScalar> > tDenseMatrix;
 
        //
        // Fields
        //
 
        Config m_cfg;                      // Configuration
        SolverState m_sst;                 // Solver state
        Pose m_pose;                       // Pose
        void* m_tag;                       // User data
        btSoftBodyWorldInfo* m_worldInfo;  // World info
        tNoteArray m_notes;                // Notes
        tNodeArray m_nodes;                // Nodes
        tRenderNodeArray m_renderNodes;    // Render Nodes
        tLinkArray m_links;                // Links
        tFaceArray m_faces;                // Faces
        tRenderFaceArray m_renderFaces;    // Faces
        tTetraArray m_tetras;              // Tetras
        btAlignedObjectArray<TetraScratch> m_tetraScratches;
        btAlignedObjectArray<TetraScratch> m_tetraScratchesTn;
        tAnchorArray m_anchors;  // Anchors
        btAlignedObjectArray<DeformableNodeRigidAnchor> m_deformableAnchors;
        tRContactArray m_rcontacts;  // Rigid contacts
        btAlignedObjectArray<DeformableNodeRigidContact> m_nodeRigidContacts;
        btAlignedObjectArray<DeformableFaceNodeContact> m_faceNodeContacts;
        btAlignedObjectArray<DeformableFaceRigidContact> m_faceRigidContacts;
        btAlignedObjectArray<DeformableFaceNodeContact> m_faceNodeContactsCCD;
        tSContactArray m_scontacts;     // Soft contacts
        tJointArray m_joints;           // Joints
        tMaterialArray m_materials;     // Materials
        btScalar m_timeacc;             // Time accumulator
        btVector3 m_bounds[2];          // Spatial bounds
        bool m_bUpdateRtCst;            // Update runtime constants
        btDbvt m_ndbvt;                 // Nodes tree
        btDbvt m_fdbvt;                 // Faces tree
        btDbvntNode* m_fdbvnt;          // Faces tree with normals
        btDbvt m_cdbvt;                 // Clusters tree
        tClusterArray m_clusters;       // Clusters
        btScalar m_dampingCoefficient;  // Damping Coefficient
        btScalar m_sleepingThreshold;
        btScalar m_maxSpeedSquared;
        btAlignedObjectArray<btVector3> m_quads;  // quadrature points for collision detection
        btScalar m_repulsionStiffness;
        btScalar m_gravityFactor;
        bool m_cacheBarycenter;
        btAlignedObjectArray<btVector3> m_X;  // initial positions
 
        btAlignedObjectArray<btVector4> m_renderNodesInterpolationWeights;
        btAlignedObjectArray<btAlignedObjectArray<const btSoftBody::Node*> > m_renderNodesParents;
        btAlignedObjectArray<btScalar> m_z;  // vertical distance used in extrapolation
        bool m_useSelfCollision;
        bool m_softSoftCollision;
 
        btAlignedObjectArray<bool> m_clusterConnectivity;  //cluster connectivity, for self-collision
 
        btVector3 m_windVelocity;
 
        btScalar m_restLengthScale;
 
        bool m_reducedModel;      // Reduced deformable model flag
        
        //
        // Api
        //
 
        /* ctor                                                                                                                                 */
        btSoftBody(btSoftBodyWorldInfo* worldInfo, int node_count, const btVector3* x, const btScalar* m);
 
        /* ctor                                                                                                                                 */
        btSoftBody(btSoftBodyWorldInfo* worldInfo);
 
        void initDefaults();
 
        /* dtor                                                                                                                                 */
        virtual ~btSoftBody();
        /* Check for existing link                                                                                              */
 
        btAlignedObjectArray<int> m_userIndexMapping;
 
        btSoftBodyWorldInfo* getWorldInfo()
        {
                return m_worldInfo;
        }
 
        void setDampingCoefficient(btScalar damping_coeff)
        {
                m_dampingCoefficient = damping_coeff;
        }

        virtual void setCollisionShape(btCollisionShape* collisionShape)
        {
        }
 
        bool checkLink(int node0,
                                   int node1) const;
        bool checkLink(const Node* node0,
                                   const Node* node1) const;
        /* Check for existing face                                                                                              */
        bool checkFace(int node0,
                                   int node1,
                                   int node2) const;
        /* Append material                                                                                                              */
        Material* appendMaterial();
        /* Append note                                                                                                                  */
        void appendNote(const char* text,
                                        const btVector3& o,
                                        const btVector4& c = btVector4(1, 0, 0, 0),
                                        Node* n0 = 0,
                                        Node* n1 = 0,
                                        Node* n2 = 0,
                                        Node* n3 = 0);
        void appendNote(const char* text,
                                        const btVector3& o,
                                        Node* feature);
        void appendNote(const char* text,
                                        const btVector3& o,
                                        Link* feature);
        void appendNote(const char* text,
                                        const btVector3& o,
                                        Face* feature);
        /* Append node                                                                                                                  */
        void appendNode(const btVector3& x, btScalar m);
        /* Append link                                                                                                                  */
        void appendLink(int model = -1, Material* mat = 0);
        void appendLink(int node0,
                                        int node1,
                                        Material* mat = 0,
                                        bool bcheckexist = false);
        void appendLink(Node* node0,
                                        Node* node1,
                                        Material* mat = 0,
                                        bool bcheckexist = false);
        /* Append face                                                                                                                  */
        void appendFace(int model = -1, Material* mat = 0);
        void appendFace(int node0,
                                        int node1,
                                        int node2,
                                        Material* mat = 0);
        void appendTetra(int model, Material* mat);
        //
        void appendTetra(int node0,
                                         int node1,
                                         int node2,
                                         int node3,
                                         Material* mat = 0);
 
        /* Append anchor                                                                                                                */
        void appendDeformableAnchor(int node, btRigidBody* body);
        void appendDeformableAnchor(int node, btMultiBodyLinkCollider* link);
        void appendAnchor(int node,
                                          btRigidBody* body, bool disableCollisionBetweenLinkedBodies = false, btScalar influence = 1);
        void appendAnchor(int node, btRigidBody* body, const btVector3& localPivot, bool disableCollisionBetweenLinkedBodies = false, btScalar influence = 1);
        void removeAnchor(int node);
        /* Append linear joint                                                                                                  */
        void appendLinearJoint(const LJoint::Specs& specs, Cluster* body0, Body body1);
        void appendLinearJoint(const LJoint::Specs& specs, Body body = Body());
        void appendLinearJoint(const LJoint::Specs& specs, btSoftBody* body);
        /* Append linear joint                                                                                                  */
        void appendAngularJoint(const AJoint::Specs& specs, Cluster* body0, Body body1);
        void appendAngularJoint(const AJoint::Specs& specs, Body body = Body());
        void appendAngularJoint(const AJoint::Specs& specs, btSoftBody* body);
        /* Add force (or gravity) to the entire body                                                    */
        void addForce(const btVector3& force);
        /* Add force (or gravity) to a node of the body                                                 */
        void addForce(const btVector3& force,
                                  int node);
        /* Add aero force to a node of the body */
        void addAeroForceToNode(const btVector3& windVelocity, int nodeIndex);
 
        /* Add aero force to a face of the body */
        void addAeroForceToFace(const btVector3& windVelocity, int faceIndex);
 
        /* Add velocity to the entire body                                                                              */
        void addVelocity(const btVector3& velocity);
 
        /* Set velocity for the entire body                                                                             */
        void setVelocity(const btVector3& velocity);
 
        /* Add velocity to a node of the body                                                                   */
        void addVelocity(const btVector3& velocity,
                                         int node);
        /* Set mass                                                                                                                             */
        void setMass(int node,
                                 btScalar mass);
        /* Get mass                                                                                                                             */
        btScalar getMass(int node) const;
        /* Get total mass                                                                                                               */
        btScalar getTotalMass() const;
        /* Set total mass (weighted by previous masses)                                                 */
        void setTotalMass(btScalar mass,
                                          bool fromfaces = false);
        /* Set total density                                                                                                    */
        void setTotalDensity(btScalar density);
        /* Set volume mass (using tetrahedrons)                                                                 */
        void setVolumeMass(btScalar mass);
        /* Set volume density (using tetrahedrons)                                                              */
        void setVolumeDensity(btScalar density);
        /* Get the linear velocity of the center of mass                        */
        btVector3 getLinearVelocity();
        /* Set the linear velocity of the center of mass                        */
        void setLinearVelocity(const btVector3& linVel);
        /* Set the angular velocity of the center of mass                       */
        void setAngularVelocity(const btVector3& angVel);
        /* Get best fit rigid transform                                         */
        btTransform getRigidTransform();
        /* Transform to given pose                                              */
        virtual void transformTo(const btTransform& trs);
        /* Transform                                                                                                                    */
        virtual void transform(const btTransform& trs);
        /* Translate                                                                                                                    */
        virtual void translate(const btVector3& trs);
        /* Rotate                                                                                                                       */
        virtual void rotate(const btQuaternion& rot);
        /* Scale                                                                                                                                */
        virtual void scale(const btVector3& scl);
        /* Get link resting lengths scale                                                                               */
        btScalar getRestLengthScale();
        /* Scale resting length of all springs                                                                  */
        void setRestLengthScale(btScalar restLength);
        /* Set current state as pose                                                                                    */
        void setPose(bool bvolume,
                                 bool bframe);
        /* Set current link lengths as resting lengths                                                  */
        void resetLinkRestLengths();
        /* Return the volume                                                                                                    */
        btScalar getVolume() const;
        /* Cluster count                                                                                                                */
        btVector3 getCenterOfMass() const
        {
                btVector3 com(0, 0, 0);
                for (int i = 0; i < m_nodes.size(); i++)
                {
                        com += (m_nodes[i].m_x * this->getMass(i));
                }
                com /= this->getTotalMass();
                return com;
        }
        int clusterCount() const;
        /* Cluster center of mass                                                                                               */
        static btVector3 clusterCom(const Cluster* cluster);
        btVector3 clusterCom(int cluster) const;
        /* Cluster velocity at rpos                                                                                             */
        static btVector3 clusterVelocity(const Cluster* cluster, const btVector3& rpos);
        /* Cluster impulse                                                                                                              */
        static void clusterVImpulse(Cluster* cluster, const btVector3& rpos, const btVector3& impulse);
        static void clusterDImpulse(Cluster* cluster, const btVector3& rpos, const btVector3& impulse);
        static void clusterImpulse(Cluster* cluster, const btVector3& rpos, const Impulse& impulse);
        static void clusterVAImpulse(Cluster* cluster, const btVector3& impulse);
        static void clusterDAImpulse(Cluster* cluster, const btVector3& impulse);
        static void clusterAImpulse(Cluster* cluster, const Impulse& impulse);
        static void clusterDCImpulse(Cluster* cluster, const btVector3& impulse);
        /* Generate bending constraints based on distance in the adjency graph  */
        int generateBendingConstraints(int distance,
                                                                   Material* mat = 0);
        /* Randomize constraints to reduce solver bias                                                  */
        void randomizeConstraints();
 
        void updateState(const btAlignedObjectArray<btVector3>& qs, const btAlignedObjectArray<btVector3>& vs);
 
        /* Release clusters                                                                                                             */
        void releaseCluster(int index);
        void releaseClusters();
        /* Generate clusters (K-mean)                                                                                   */
        int generateClusters(int k, int maxiterations = 8192);
        /* Refine                                                                                                                               */
        void refine(ImplicitFn* ifn, btScalar accurary, bool cut);
        /* CutLink                                                                                                                              */
        bool cutLink(int node0, int node1, btScalar position);
        bool cutLink(const Node* node0, const Node* node1, btScalar position);

        bool rayTest(const btVector3& rayFrom,
                                 const btVector3& rayTo,
                                 sRayCast& results);
        bool rayFaceTest(const btVector3& rayFrom,
                                         const btVector3& rayTo,
                                         sRayCast& results);
        int rayFaceTest(const btVector3& rayFrom, const btVector3& rayTo,
                                        btScalar& mint, int& index) const;
        /* Solver presets                                                                                                               */
        void setSolver(eSolverPresets::_ preset);
        /* predictMotion                                                                                                                */
        void predictMotion(btScalar dt);
        /* solveConstraints                                                                                                             */
        void solveConstraints();
        /* staticSolve                                                                                                                  */
        void staticSolve(int iterations);
        /* solveCommonConstraints                                                                                               */
        static void solveCommonConstraints(btSoftBody** bodies, int count, int iterations);
        /* solveClusters                                                                                                                */
        static void solveClusters(const btAlignedObjectArray<btSoftBody*>& bodies);
        /* integrateMotion                                                                                                              */
        void integrateMotion();
        /* defaultCollisionHandlers                                                                                             */
        void defaultCollisionHandler(const btCollisionObjectWrapper* pcoWrap);
        void defaultCollisionHandler(btSoftBody* psb);
        void setSelfCollision(bool useSelfCollision);
        bool useSelfCollision();
        void updateDeactivation(btScalar timeStep);
        void setZeroVelocity();
        bool wantsSleeping();
 
        virtual btMatrix3x3 getImpulseFactor(int n_node)
        {
                btMatrix3x3 tmp;
                tmp.setIdentity();
                return tmp;
        }
 
        //
        // Functionality to deal with new accelerated solvers.
        //

        void setWindVelocity(const btVector3& velocity);

        const btVector3& getWindVelocity();
 
        //
        // Set the solver that handles this soft body
        // Should not be allowed to get out of sync with reality
        // Currently called internally on addition to the world
        void setSoftBodySolver(btSoftBodySolver* softBodySolver)
        {
                m_softBodySolver = softBodySolver;
        }
 
        //
        // Return the solver that handles this soft body
        //
        btSoftBodySolver* getSoftBodySolver()
        {
                return m_softBodySolver;
        }
 
        //
        // Return the solver that handles this soft body
        //
        btSoftBodySolver* getSoftBodySolver() const
        {
                return m_softBodySolver;
        }
 
        //
        // Cast
        //
 
        static const btSoftBody* upcast(const btCollisionObject* colObj)
        {
                if (colObj->getInternalType() == CO_SOFT_BODY)
                        return (const btSoftBody*)colObj;
                return 0;
        }
        static btSoftBody* upcast(btCollisionObject* colObj)
        {
                if (colObj->getInternalType() == CO_SOFT_BODY)
                        return (btSoftBody*)colObj;
                return 0;
        }
 
        //
        // ::btCollisionObject
        //
 
        virtual void getAabb(btVector3& aabbMin, btVector3& aabbMax) const
        {
                aabbMin = m_bounds[0];
                aabbMax = m_bounds[1];
        }
        //
        // Private
        //
        void pointersToIndices();
        void indicesToPointers(const int* map = 0);
 
        int rayTest(const btVector3& rayFrom, const btVector3& rayTo,
                                btScalar& mint, eFeature::_& feature, int& index, bool bcountonly) const;
        void initializeFaceTree();
        void rebuildNodeTree();
        btVector3 evaluateCom() const;
        bool checkDeformableContact(const btCollisionObjectWrapper* colObjWrap, const btVector3& x, btScalar margin, btSoftBody::sCti& cti, bool predict = false) const;
        bool checkDeformableFaceContact(const btCollisionObjectWrapper* colObjWrap, Face& f, btVector3& contact_point, btVector3& bary, btScalar margin, btSoftBody::sCti& cti, bool predict = false) const;
        bool checkContact(const btCollisionObjectWrapper* colObjWrap, const btVector3& x, btScalar margin, btSoftBody::sCti& cti) const;
        void updateNormals();
        void updateBounds();
        void updatePose();
        void updateConstants();
        void updateLinkConstants();
        void updateArea(bool averageArea = true);
        void initializeClusters();
        void updateClusters();
        void cleanupClusters();
        void prepareClusters(int iterations);
        void solveClusters(btScalar sor);
        void applyClusters(bool drift);
        void dampClusters();
        void setSpringStiffness(btScalar k);
        void setGravityFactor(btScalar gravFactor);
        void setCacheBarycenter(bool cacheBarycenter);
        void initializeDmInverse();
        void updateDeformation();
        void advanceDeformation();
        void applyForces();
        void setMaxStress(btScalar maxStress);
        void interpolateRenderMesh();
        void setCollisionQuadrature(int N);
        static void PSolve_Anchors(btSoftBody* psb, btScalar kst, btScalar ti);
        static void PSolve_RContacts(btSoftBody* psb, btScalar kst, btScalar ti);
        static void PSolve_SContacts(btSoftBody* psb, btScalar, btScalar ti);
        static void PSolve_Links(btSoftBody* psb, btScalar kst, btScalar ti);
        static void VSolve_Links(btSoftBody* psb, btScalar kst);
        static psolver_t getSolver(ePSolver::_ solver);
        static vsolver_t getSolver(eVSolver::_ solver);
        void geometricCollisionHandler(btSoftBody* psb);
#define SAFE_EPSILON SIMD_EPSILON * 100.0
        void updateNode(btDbvtNode* node, bool use_velocity, bool margin)
        {
                if (node->isleaf())
                {
                        btSoftBody::Node* n = (btSoftBody::Node*)(node->data);
                        ATTRIBUTE_ALIGNED16(btDbvtVolume)
                        vol;
                        btScalar pad = margin ? m_sst.radmrg : SAFE_EPSILON;  // use user defined margin or margin for floating point precision
                        if (use_velocity)
                        {
                                btVector3 points[2] = {n->m_x, n->m_x + m_sst.sdt * n->m_v};
                                vol = btDbvtVolume::FromPoints(points, 2);
                                vol.Expand(btVector3(pad, pad, pad));
                        }
                        else
                        {
                                vol = btDbvtVolume::FromCR(n->m_x, pad);
                        }
                        node->volume = vol;
                        return;
                }
                else
                {
                        updateNode(node->childs[0], use_velocity, margin);
                        updateNode(node->childs[1], use_velocity, margin);
                        ATTRIBUTE_ALIGNED16(btDbvtVolume)
                        vol;
                        Merge(node->childs[0]->volume, node->childs[1]->volume, vol);
                        node->volume = vol;
                }
        }
 
        void updateNodeTree(bool use_velocity, bool margin)
        {
                if (m_ndbvt.m_root)
                        updateNode(m_ndbvt.m_root, use_velocity, margin);
        }
 
        template <class DBVTNODE>  // btDbvtNode or btDbvntNode
        void updateFace(DBVTNODE* node, bool use_velocity, bool margin)
        {
                if (node->isleaf())
                {
                        btSoftBody::Face* f = (btSoftBody::Face*)(node->data);
                        btScalar pad = margin ? m_sst.radmrg : SAFE_EPSILON;  // use user defined margin or margin for floating point precision
                        ATTRIBUTE_ALIGNED16(btDbvtVolume)
                        vol;
                        if (use_velocity)
                        {
                                btVector3 points[6] = {f->m_n[0]->m_x, f->m_n[0]->m_x + m_sst.sdt * f->m_n[0]->m_v,
                                                                           f->m_n[1]->m_x, f->m_n[1]->m_x + m_sst.sdt * f->m_n[1]->m_v,
                                                                           f->m_n[2]->m_x, f->m_n[2]->m_x + m_sst.sdt * f->m_n[2]->m_v};
                                vol = btDbvtVolume::FromPoints(points, 6);
                        }
                        else
                        {
                                btVector3 points[3] = {f->m_n[0]->m_x,
                                                                           f->m_n[1]->m_x,
                                                                           f->m_n[2]->m_x};
                                vol = btDbvtVolume::FromPoints(points, 3);
                        }
                        vol.Expand(btVector3(pad, pad, pad));
                        node->volume = vol;
                        return;
                }
                else
                {
                        updateFace(node->childs[0], use_velocity, margin);
                        updateFace(node->childs[1], use_velocity, margin);
                        ATTRIBUTE_ALIGNED16(btDbvtVolume)
                        vol;
                        Merge(node->childs[0]->volume, node->childs[1]->volume, vol);
                        node->volume = vol;
                }
        }
        void updateFaceTree(bool use_velocity, bool margin)
        {
                if (m_fdbvt.m_root)
                        updateFace(m_fdbvt.m_root, use_velocity, margin);
                if (m_fdbvnt)
                        updateFace(m_fdbvnt, use_velocity, margin);
        }
 
        template <typename T>
        static inline T BaryEval(const T& a,
                                                         const T& b,
                                                         const T& c,
                                                         const btVector3& coord)
        {
                return (a * coord.x() + b * coord.y() + c * coord.z());
        }
 
        void applyRepulsionForce(btScalar timeStep, bool applySpringForce)
        {
                btAlignedObjectArray<int> indices;
                {
                        // randomize the order of repulsive force
                        indices.resize(m_faceNodeContacts.size());
                        for (int i = 0; i < m_faceNodeContacts.size(); ++i)
                                indices[i] = i;
#define NEXTRAND (seed = (1664525L * seed + 1013904223L) & 0xffffffff)
                        int i, ni;
 
                        for (i = 0, ni = indices.size(); i < ni; ++i)
                        {
                                btSwap(indices[i], indices[NEXTRAND % ni]);
                        }
                }
                for (int k = 0; k < m_faceNodeContacts.size(); ++k)
                {
                        int idx = indices[k];
                        btSoftBody::DeformableFaceNodeContact& c = m_faceNodeContacts[idx];
                        btSoftBody::Node* node = c.m_node;
                        btSoftBody::Face* face = c.m_face;
                        const btVector3& w = c.m_bary;
                        const btVector3& n = c.m_normal;
                        btVector3 l = node->m_x - BaryEval(face->m_n[0]->m_x, face->m_n[1]->m_x, face->m_n[2]->m_x, w);
                        btScalar d = c.m_margin - n.dot(l);
                        d = btMax(btScalar(0), d);
 
                        const btVector3& va = node->m_v;
                        btVector3 vb = BaryEval(face->m_n[0]->m_v, face->m_n[1]->m_v, face->m_n[2]->m_v, w);
                        btVector3 vr = va - vb;
                        const btScalar vn = btDot(vr, n);  // dn < 0 <==> opposing
                        if (vn > OVERLAP_REDUCTION_FACTOR * d / timeStep)
                                continue;
                        btVector3 vt = vr - vn * n;
                        btScalar I = 0;
                        btScalar mass = node->m_im == 0 ? 0 : btScalar(1) / node->m_im;
                        if (applySpringForce)
                                I = -btMin(m_repulsionStiffness * timeStep * d, mass * (OVERLAP_REDUCTION_FACTOR * d / timeStep - vn));
                        if (vn < 0)
                                I += 0.5 * mass * vn;
                        int face_penetration = 0, node_penetration = node->m_constrained;
                        for (int i = 0; i < 3; ++i)
                                face_penetration |= face->m_n[i]->m_constrained;
                        btScalar I_tilde = 2.0 * I / (1.0 + w.length2());
 
                        //             double the impulse if node or face is constrained.
                        if (face_penetration > 0 || node_penetration > 0)
                        {
                                I_tilde *= 2.0;
                        }
                        if (face_penetration <= 0)
                        {
                                for (int j = 0; j < 3; ++j)
                                        face->m_n[j]->m_v += w[j] * n * I_tilde * node->m_im;
                        }
                        if (node_penetration <= 0)
                        {
                                node->m_v -= I_tilde * node->m_im * n;
                        }
 
                        // apply frictional impulse
                        btScalar vt_norm = vt.safeNorm();
                        if (vt_norm > SIMD_EPSILON)
                        {
                                btScalar delta_vn = -2 * I * node->m_im;
                                btScalar mu = c.m_friction;
                                btScalar vt_new = btMax(btScalar(1) - mu * delta_vn / (vt_norm + SIMD_EPSILON), btScalar(0)) * vt_norm;
                                I = 0.5 * mass * (vt_norm - vt_new);
                                vt.safeNormalize();
                                I_tilde = 2.0 * I / (1.0 + w.length2());
                                //                 double the impulse if node or face is constrained.
                                if (face_penetration > 0 || node_penetration > 0)
                                        I_tilde *= 2.0;
                                if (face_penetration <= 0)
                                {
                                        for (int j = 0; j < 3; ++j)
                                                face->m_n[j]->m_v += w[j] * vt * I_tilde * (face->m_n[j])->m_im;
                                }
                                if (node_penetration <= 0)
                                {
                                        node->m_v -= I_tilde * node->m_im * vt;
                                }
                        }
                }
        }
        virtual int calculateSerializeBufferSize() const;

        virtual const char* serialize(void* dataBuffer, class btSerializer* serializer) const;
};
 
#endif  //_BT_SOFT_BODY_H