bullet3/examples/Experiments/ImplicitCloth/stan/SpringNetwork.h

#ifndef STAN_SPRING_NETWORK_H
#define STAN_SPRING_NETWORK_H

#include "vec3n.h"

#define SPRING_STRUCT (0)
#define SPRING_SHEAR  (1)
#define SPRING_BEND   (2)


class SpringNetwork
{
 public:
       class Spring
       {
        public:
               int type;          // index into coefficients spring_k[]
               float restlen;
               int a,b;      // spring endpoints vector indices
               int iab,iba;  // indices into off-diagonal blocks of sparse matrix
               Spring(){}
               Spring(int _type,int _a,int _b,float _restlen):type(_type),a(_a),b(_b),restlen(_restlen){iab=iba=-1;}
       };
       Array<Spring> springs;
       float3N     X;    // positions of all points
       float3N     V;    // velocities
       float3N     F;    // force on each point
       float3N     dV;   // change in velocity
       float3Nx3N  A;    // big matrix we solve system with
       float3Nx3N  dFdX; // big matrix of derivative of force wrt position
       float3Nx3N  dFdV; // big matrix of derivative of force wrt velocity
       float3Nx3N  S;    // used for our constraints - contains only some diagonal blocks as needed S[i,i]
       int awake;
       float3 bmin,bmax;
       union
       {
               struct
               {
                       float spring_struct;
                       float spring_shear;
                       float spring_bend;
               };
               float spring_k[3];
       };
       float  spring_damp;
       float  spring_air;
       float  cloth_step;  // delta time for cloth
       float3 cloth_gravity;
       float  cloth_sleepthreshold;
       int    cloth_sleepcount;

       SpringNetwork(int _n);
       Spring &AddBlocks(Spring &s);
       Spring &CreateSpring(int type,int a,int b,float restlen){return AddBlocks(springs.Add(Spring(type,a,b,restlen)));}
       Spring &CreateSpring(int type,int a,int b){return CreateSpring(type,a,b,magnitude(X[b]-X[a]));}
       void    UpdateLimits() { BoxLimits(X.element,X.count,bmin,bmax);}
       void    Wake(){awake=cloth_sleepcount;}
       void    Simulate(float dt);
       void    PreSolveSpring(const Spring &s);
       void    CalcForces();
};

#endif //STAN_SPRING_NETWORK_H