edge.h

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/**
 *\file         edge.h
 *
 *              
 *\brief        Define HALF edge (no EDGE in euler!)
 *
 *              1. From a *pure perspective* of topological plane model of a closed     
 *                 2-manifold, there are actually no such things as edges, instead,     
 *                 there are only half edges, with the condition each is identified to  
 *                 exactly another one. Therefore, there is no edge nodes in my         
 *                 design. The identification is archived by storing the opposite half  
 *                 edge in the half edge node (member o).                               
 *                                                                                      
 *              2. All half edges, including circular edge (end points coincident), have
 *                 their oppositive halves, except singular half edge, i.e., of zero length,
 *                 which has nil as its opposite half edge link.
 * 
 *              3. Because there are only half edges, we simple use edge_t to denote the 
 *                 actually half edge type.
 *
 *\author       Xianming Chen\n
 *              Computer Science Department\n
 *              University of Utah
 *
 *\date         15 Aug 2006\n
 *              Copyright (c) 2006, University of Utah
 */


#ifndef _EDGE_H
#define _EDGE_H

#include "node_fwd_dcl.h"
#include <utility>
#include <cassert>


namespace euler
{
  class edge_t
  {
  public:
      loop_t *l;
      edge_t *o;
      edge_t *pre, *nxt;
      vertex_t *v;

  private:
      edge_t(vertex_t* v, loop_t* l) : l(l), o(0), pre(this), nxt(this), v(v)           { assert(! l->e); l->e = this; }
      edge_t(vertex_t* v, edge_t *nxt) : l(nxt->l), o(0), pre(nxt->pre), nxt(nxt), v(v) { nxt->pre->nxt = this; nxt->pre = this; }

      friend class solid_t;
      friend class loop_t;
  };


}


#endif

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