Mesh Library - HalfEdge

struct halfedge{


	Edge     *hedge;
	Loop     *hloop;
	Vertex   *hvert;

	HalfEdge *next;
	HalfEdge *prev;

	int     aliveh;

};

• hedge - the nonoriented edge to which the current halfedge is attached.
• hloop - the loop structure, the current halfedge belongs to
• hvert - starting vertex of current halfedge
• next,prev - halfedge pointers in the loop. Next pointer are arranged so that the loop is ccw
• aliveh- indicating if current halfedge is alive

• void HalfEdgeConstruct( Loop **l, Vertex * s);
  construct a halfedge within the loop l, with starting vertex s

• void HalfEdgeDestruct( HalfEdge ** l);
  Destruct the halfedge l

• HalfEdge * HalfEdgeMate( HalfEdge * l);
  Find the mate of halfedge l, suppose it is r. Then l and r have the same vertices, but opposite orientation

• Vertex * HalfEdgeStartVertex( HalfEdge * l);
  Find the starting vertex of halfedge l.

• Vertex * HalfEdgeEndVertex( HalfEdge * l);
  Find the ending vertex of halfedge l

• void HalfEdgeMerge( HalfEdge * l);
  

  Edge Collapse

  In the mesh, merge the end vertex of l to the start vertex of l, change all neighor structures of l, keep the mesh still a manifold. The neighor structures are inactive, not not really removed.

• void HalfEdgeExtend( HalfEdge * l);
  

  Vertex Split

  Suppose after edge collapsation, l is the last halfedge collapsed, then recover the mesh by extending l again.

• double HalfEdgeCost( HalfEdge * , double ( * )( Face * ) );
  Given cost function of face, calculate halfedge cost.