Splines to Gcode from dxf file

void SPLINE_FEED(double x1, double y1, double x2, double y2, double x3, double y3) {
    double x0 = 0;
    double y0 = 0;
    pvec_v.push_back({0,0,0});

    for(int i=1; i<=100; i++) {      double t = i / 100.;
        double t3 = t*t*t;
        double t2 = 3*t*t*(1-t);
        double t1 = 3*t*(1-t)*(1-t);
        double t0 = (1-t)*(1-t)*(1-t);
        double x = x0*t0 + x1*t1 + x2*t2 + x3*t3;
        double y = y0*t0 + y1*t1 + y2*t2 + y3*t3;
        double z = 0;

        pvec_v.push_back({x,y,z});
    }
}

void cubic_spline(){

    std::vector<std::vector<double>> C; //2d array
    C.push_back({0,0});
    C.push_back({100,50});
    C.push_back({200,-50});
    C.push_back({300,50});

    double S[C.size()-1][2][4];
    double w, b[C.size()], d[C.size()], x[C.size()];
    int i, dim;
    int n = C.size()-1; // number of splines

    for(dim=0; dim<2; dim++)
    {
        // define d[]:
        d[0]=3.0*(C[1][dim]-C[0][dim]);
        for(i=1; i<n; i++)
            d[i]=3.0*(C[i+1][dim]-C[i-1][dim]);
        d[n]=3.0*(C[n][dim]-C[n-1][dim]);
        // forward sweep: (simplified tridiagonal solution: all a[i]=1 and all c[i]=1)
        b[0]=2.0;
        for(i=1; i<C.size(); i++)
        {
            w = 1.0/b[i-1];
            b[i] = 4.0 - w;
            d[i] -= (w*d[i-1]);
        }
        // calculate solution vector x[i] = D[i]:
        // (Wikipedia x[] = Wolfram D[])
        x[n]=d[n]/b[n];
        for(i=n-1; i>=0; i--)
            x[i]=(d[i]-x[i+1])/b[i];
        // calculate spline S[i][dim] a, b, c and d:
        for(i=0; i<n; i++)
        {
            S[i][dim][0]=C[i][dim];
            S[i][dim][1]=x[i];
            S[i][dim][2]=3.0*(C[i+1][dim]-C[i][dim]) - 2.0*x[i] - x[i+1];
            S[i][dim][3]=2.0*(C[i][dim]-C[i+1][dim]) + x[i] + x[i+1];
        }
    }

    for(int p=0; p<C.size()-1; p++)  //spline points
    {
        for(double t=0; t<1; t+=0.01)  //time 0-1 for each spline
        {
            double px = ((S[p][0][3]*t+S[p][0][2])*t+S[p][0][1])*t+S[p][0][0];
            double py = ((S[p][1][3]*t+S[p][1][2])*t+S[p][1][1])*t+S[p][1][0];
            //std::cout<< "x:" << px << " y:" << py << std::endl;
            pvec_a.push_back({px,py,0});
        }
    }

}

void MainWindow::on_pushButton_pressed()
{
    //!
    Handle(AIS_Shape) ashape=draw_primitives().draw_3d_origin({0,0,0},5);
    OpencascadeWidget->show_shape(ashape);
    ashape=draw_primitives().draw_3d_origin({100,50,0},5);
    OpencascadeWidget->show_shape(ashape);
    ashape=draw_primitives().draw_3d_origin({200,-50,0},5);
    OpencascadeWidget->show_shape(ashape);
     ashape=draw_primitives().draw_3d_origin({300,50,0},5);
    OpencascadeWidget->show_shape(ashape);
    OpencascadeWidget->Redraw();

    SPLINE_FEED(100,50,200,-50,300,50);

    cubic_spline(); //black

    gp_Pnt p;
    std::vector<gp_Pnt> pvec;
    p.SetXYZ({0,0,0});
    pvec.push_back(p);
    p.SetXYZ({100,50,0});
    pvec.push_back(p);
    p.SetXYZ({200,-50,0});
    pvec.push_back(p);
    p.SetXYZ({300,50,0});
    pvec.push_back(p);
    ashape=draw_primitives().draw_3d_spline(pvec,10);
    OpencascadeWidget->show_shape(ashape);
    ashape=draw_primitives().colorize(ashape,Quantity_NOC_GREEN,0); //green
    OpencascadeWidget->Redraw();

    draw_result();
}