构建一个立方体

• 对于每个程序，第一步是定义您的MyMesh类型。 OpenMesh支持常规多边形网格（面是具有不同数量顶点的多边形）以及专用三角形网格（所有面都是三角形）。 在这个例子中，我们想要从六个四边形构建一个立方体，因此我们选择多边形网格。
• OpenMesh还支持不同的网格内核，指定内部存储所有顶点，边和面的方式（另请参见网格内核）。 但是，存储必须提供类似接口的数组。 对于本教程，我们使用提供的ArrayKernel。 TriMesh / PolyMesh和内核的预定义组合包含在OpenMesh / src / OpenMesh / Core / Mesh中，我们使用PolyMesh_ArrayKernelT。
• 
• 既然我们已经声明了MyMesh类型，我们只需要添加8个顶点和6个四边形来构建一个立方体。 使用add_vertex方法添加顶点。 它获取一个坐标并返回插入顶点的句柄。 我们将所有句柄存储在一个数组中，因为我们需要它们来指定面。
• 
• 为了向网格添加一个面，我们必须构建一个矢量，将手柄保持在面的顶点。 此向量将传递给add_face方法。 以下块将从前四个顶点创建一个面：
• 面的方向由顶点的给定顺序定义：如果查看多边形的前面，则顶点按逆时针顺序排列。
• 在创建了所有六个面之后，我们希望将生成的网格写入标准输出。 OpenMesh在命名空间OpenMesh :: IO中提供了一些基本的输入/输出方法：
• 要使用OpenMesh的IO工具，请确保首先包含包含MeshIO.hh。
• 示例源代码

• /* ========================================================================= *
   *                                                                           *
   *                               OpenMesh                                    *
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   *           Department of Computer Graphics and Multimedia                  *
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  /*===========================================================================*\
   *                                                                           *
   *   $Revision$                                                         *
   *   $Date$                   *
   *                                                                           *
  \*===========================================================================*/
  #include 
  // -------------------- OpenMesh
  #include 
  #include 
  // ----------------------------------------------------------------------------
  typedef OpenMesh::PolyMesh_ArrayKernelT<>  MyMesh;
  // ----------------------------------------------------------------------------
  // Build a simple cube and write it to std::cout
    
  int main()
  {
    MyMesh mesh;
    // generate vertices
    MyMesh::VertexHandle vhandle[8];
    vhandle[0] = mesh.add_vertex(MyMesh::Point(-1, -1,  1));
    vhandle[1] = mesh.add_vertex(MyMesh::Point( 1, -1,  1));
    vhandle[2] = mesh.add_vertex(MyMesh::Point( 1,  1,  1));
    vhandle[3] = mesh.add_vertex(MyMesh::Point(-1,  1,  1));
    vhandle[4] = mesh.add_vertex(MyMesh::Point(-1, -1, -1));
    vhandle[5] = mesh.add_vertex(MyMesh::Point( 1, -1, -1));
    vhandle[6] = mesh.add_vertex(MyMesh::Point( 1,  1, -1));
    vhandle[7] = mesh.add_vertex(MyMesh::Point(-1,  1, -1));
    // generate (quadrilateral) faces
    std::vector  face_vhandles;
    face_vhandles.clear();
    face_vhandles.push_back(vhandle[0]);
    face_vhandles.push_back(vhandle[1]);
    face_vhandles.push_back(vhandle[2]);
    face_vhandles.push_back(vhandle[3]);
    mesh.add_face(face_vhandles);
   
    face_vhandles.clear();
    face_vhandles.push_back(vhandle[7]);
    face_vhandles.push_back(vhandle[6]);
    face_vhandles.push_back(vhandle[5]);
    face_vhandles.push_back(vhandle[4]);
    mesh.add_face(face_vhandles);
    face_vhandles.clear();
    face_vhandles.push_back(vhandle[1]);
    face_vhandles.push_back(vhandle[0]);
    face_vhandles.push_back(vhandle[4]);
    face_vhandles.push_back(vhandle[5]);
    mesh.add_face(face_vhandles);
    face_vhandles.clear();
    face_vhandles.push_back(vhandle[2]);
    face_vhandles.push_back(vhandle[1]);
    face_vhandles.push_back(vhandle[5]);
    face_vhandles.push_back(vhandle[6]);
    mesh.add_face(face_vhandles);
    face_vhandles.clear();
    face_vhandles.push_back(vhandle[3]);
    face_vhandles.push_back(vhandle[2]);
    face_vhandles.push_back(vhandle[6]);
    face_vhandles.push_back(vhandle[7]);
    mesh.add_face(face_vhandles);
    face_vhandles.clear();
    face_vhandles.push_back(vhandle[0]);
    face_vhandles.push_back(vhandle[3]);
    face_vhandles.push_back(vhandle[7]);
    face_vhandles.push_back(vhandle[4]);
    mesh.add_face(face_vhandles);
    // write mesh to output.obj
    try
    {
      if ( !OpenMesh::IO::write_mesh(mesh, "output.off") )
      {
        std::cerr << "Cannot write mesh to file 'output.off'" << std::endl;
        return 1;
      }
    }
    catch( std::exception& x )
    {
      std::cerr << x.what() << std::endl;
      return 1;
    }
    return 0;
  }