Particle *np = particle->nbs[j].neighbour;

    vec3  r = particle->x - np->x;
    float r_length = glm::length(r);

    float distDiff = r_length - restDistance;

    if(distDiff >= 0 ) continue;

    //Frictional Constraint
    vec3 n   = r/r_length;
    vec3 xxi = particle->x - xi[particle->getIndex()];
    vec3 xxj = np->x - xi[np->getIndex()];

    vec3 tangentialDisplacement = (xxi - xxj) - glm::dot(xxi - xxj, n) * n;

    float td_length = glm::length(tangentialDisplacement);

    float genMass = ( imass / (imass + imass) );


    if(td_length < (staticFriciton * distDiff)){
        particle->x += genMass * tangentialDisplacement;

        np->x += -genMass * tangentialDisplacement;
    }else{
        float upper = kineticFriction * distDiff;
        particle->x += genMass * tangentialDisplacement * std::min(upper/td_length, 1.f);

        np->x += -genMass * tangentialDisplacement * std::min(upper/td_length, 1.f);
    }