半边数据结构：
网格的顶点，边，面的数据储存在半边数据结构中，半边数据结构写成类似于C语言如下：
半边：
struct HE_edge
{
HE_vert* vert; // vertex at the end of the half-edge
HE_edge* pair; // oppositely oriented adjacent half-edge
HE_face* face; // face the half-edge borders
HE_edge* next; // next half-edge around the face
};
顶点
struct HE_vert
{
float x;
float y;
float z;
HE_edge* edge; // one of the half-edges emantating from the vertex
};
面：
struct HE_face
{
HE_edge* edge; // one of the half-edges bordering the face
};
