OpenGLでグリッドを描く

// グリッド一つ分
class cell {
  glm::vec3 _min;  //始点
  glm::vec3 _vecx; //方向1
  glm::vec3 _vecy; //方向2

public:
  cell(glm::vec3 _min_, glm::vec3 _vec_x, glm::vec3 _vec_y) {
    _min = _min_;
    _vecx = _vec_x;
    _vecy = _vec_y;
  }
  const glm::vec3& cmin()const {
    return _min;
  }
  const glm::vec3& cvecx()const {
    return _vecx;
  }
  const glm::vec3& cvecy()const {
    return _vecy;
  }

  // セルの中心
  glm::vec3 center()const {
    return _min + _vecx / 2.f + _vecy / 2.f;
  }
};

class grid {
  std::vector<cell> _cells;
  int _xcount;
  int _ycount;
  float _xwidth;
  float _ywidth;
  glm::vec3 _center;

public:

  size_t cellCount()const {
    return _cells.size();
  }
  cell& operator[](const size_t index) {
    return _cells[index];
  }
  const cell& operator[](const size_t index)const {
    return _cells[index];
  }
  grid() {}

  grid(const grid& g) {
    _cells = g._cells;
    _xcount = g._xcount;
    _ycount = g._ycount;
    _xwidth = g._xwidth;
    _ywidth = g._ywidth;
    _center = g._center;
  }
  grid& operator=(const grid& g) {
    _cells = g._cells;
    _xcount = g._xcount;
    _ycount = g._ycount;
    _xwidth = g._xwidth;
    _ywidth = g._ywidth;
    _center = g._center;
  }
  grid& operator=(grid&& g) {
    _cells = std::move(g._cells);
    _xcount = g._xcount;
    _ycount = g._ycount;
    _xwidth = g._xwidth;
    _ywidth = g._ywidth;
    _center = g._center;
    return *this;
  }

  // 平面一つ分。xcount × ycountのcellからなる
  grid(
    const glm::vec3 vecX,
    const glm::vec3 vecY,
    const glm::vec3 center,
    const float width,
    const float height,
    const int xcount,
    const int ycount) {

    _xcount = xcount;
    _ycount = ycount;
    _xwidth = width;
    _ywidth = height;

    _center = center;

    glm::vec3 NVecX = glm::normalize(vecX);
    glm::vec3 NVecY = glm::normalize(vecY);

    ////////////////////
    _cells.clear();

    // セル一個の縦方向、横方向のベクトル。長さはセル一個分
    const glm::vec3 CellVX = NVecX * (_xwidth / xcount);
    const glm::vec3 CellVY = NVecY * (_ywidth / ycount);

    // 面の始点
    const glm::vec3 Start = _center - NVecX * _xwidth / 2.f - NVecY * _ywidth / 2.f;

    for (size_t y = 0; y < ycount; y++) {
      for (size_t x = 0; x < xcount; x++) {

        // 各セルの始点
        glm::vec3 from =
          Start +
          CellVX * (float)x + CellVY * (float)y;

        // セルを記録
        _cells.push_back(
          cell(
            from,
            CellVX,
            CellVY
          )
        );

      }
    }

  }


  /*
  p0    p3
  +---------+
  |     |
  |     |
  |     |
  |     |
  +---------+
  p1    p2
  */
  glm::vec3 p0(const size_t index)const {
    return _cells[index].cmin();
  }
  glm::vec3 p1(const size_t index)const {

    return
      _cells[index].cmin() +
      _cells[index].cvecx();
  }
  glm::vec3 p2(const size_t index) const {
    return
      _cells[index].cmin() +
      _cells[index].cvecx() +
      _cells[index].cvecy();
  }
  glm::vec3 p3(const size_t index) const {
    return
      _cells[index].cmin() +
      _cells[index].cvecy();
  }

};

//! @brief グリッドを表示
//! @param [in] g グリッドオブジェクト
//! @param [in] dispcenter セルの中央を表示するか
void drawGrid(const grid& g, const bool dispcenter) {

  glLineWidth(1);
  glColor3d(1, 1, 1);
  for (size_t i = 0; i < g.cellCount(); i++) {
    glBegin(GL_LINE_LOOP);
    glVertex3fv(glm::value_ptr(g.p0(i)));
    glVertex3fv(glm::value_ptr(g.p1(i)));
    glVertex3fv(glm::value_ptr(g.p2(i)));
    glVertex3fv(glm::value_ptr(g.p3(i)));

    glEnd();
  }

  if (dispcenter) {
    glPointSize(1);
    glColor3d(1, 1, 1);
    glBegin(GL_POINTS);
    for (size_t i = 0; i < g.cellCount(); i++) {
      glVertex3fv(
        glm::value_ptr(g[i].center()));
    }
    glEnd();
  }
}

grid g(
  glm::vec3(1,0,0),
  glm::vec3(0,1,0),
  glm::vec3(0,0,0),
  4.f,4.f,
  10,10
);

drawGrid(g, false);