void IMDLtorus(Model *m, int num, double r1, double r2){
  int i,j;
  double cx,cy,cx2,cy2;
  m->num_s = num * num;
  m->surf = (Surface *)malloc(sizeof(Surface)*(m->num_s));
  for(i=0;i<num;i++){
    cx = r1*cos(2.0*M_PAI/num*i);
    cy = r1*sin(2.0*M_PAI/num*i);
    cx2 = r1*cos(2.0*M_PAI/num*(i+1));
    cy2 = r1*sin(2.0*M_PAI/num*(i+1));
    for(j=0;j<num;j++){
      m->surf[i*num+j].num_v = 4;
      m->surf[i*num+j].vertex = (Vertex *)malloc(sizeof(Vertex)*(m->surf[j].num_v));
  m->surf[i*num+j].vertex[0].x = cx2 + r2 * cos(2.0*M_PAI/num*j) * cos(2.0*M_PAI/num*(i+1));
  m->surf[i*num+j].vertex[0].y = cy2 + r2 * cos(2.0*M_PAI/num*j) * sin(2.0*M_PAI/num*(i+1));
  m->surf[i*num+j].vertex[0].z = r2 * sin(2.0*M_PAI/num*j);
  m->surf[i*num+j].vertex[1].x = cx2 + r2 * cos(2.0*M_PAI/num*(j+1)) * cos(2.0*M_PAI/num*(i+1));
  m->surf[i*num+j].vertex[1].y = cy2 + r2 * cos(2.0*M_PAI/num*(j+1)) * sin(2.0*M_PAI/num*(i+1));
  m->surf[i*num+j].vertex[1].z = r2 * sin(2.0*M_PAI/num*(j+1));
  m->surf[i*num+j].vertex[2].x = cx + r2 * cos(2.0*M_PAI/num*(j+1)) * cos(2.0*M_PAI/num*i);
  m->surf[i*num+j].vertex[2].y = cy + r2 * cos(2.0*M_PAI/num*(j+1)) * sin(2.0*M_PAI/num*i);
  m->surf[i*num+j].vertex[2].z = r2 * sin(2.0*M_PAI/num*(j+1));
  m->surf[i*num+j].vertex[3].x = cx + r2 * cos(2.0*M_PAI/num*j) * cos(2.0*M_PAI/num*i);
  m->surf[i*num+j].vertex[3].y = cy + r2 * cos(2.0*M_PAI/num*j) * sin(2.0*M_PAI/num*i);
  m->surf[i*num+j].vertex[3].z = r2 * sin(2.0*M_PAI/num*j);
       }
    }
}