code: private Vertex[] getVertexesLineFirst()
      {
          Vertex[] vertexes = new Vertex[size];
          int i = 0;
          for (List<Vertex> vertexList : this.vertexes)
          {
              for (Vertex v : vertexList)
              {
                  v.index = i;    // 设置id
                  vertexes[i++] = v;
              }
          }
  
          return vertexes;
      }
docs: 获取顶点数组
  
  @return Vertex[] 按行优先列次之的顺序构造的顶点数组