mef.cpp

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/**
 *\file         mef.cpp
 *
 *\brief        subdivide an edge loop.
 *
 *              mef(e1, e2): subdivide edge loop (the loop l1 of e1, and the loop l2 of e2,  
 *              are assumed to be from the same loop) into v1v2+[e2, e1) (change in place), and v2v1+[e1,e2) (as new edge loop of new face).
 *
 *              It sets the new half edges to the loop headers, and returns the loop in the new face.
 *
 *
 *\image        html mef.jpg
 *
 *\author       Xianming Chen\n
 *              Computer Science Department\n
 *              University of Utah
 *
 *\date          16 Aug 2006\n
 *              Copyright (c) 2006, University of Utah
 */


#include <cassert>
#include "print.h"


namespace euler
{

  loop_t* solid_t :: mef(edge_t* e1, edge_t* e2)
  {
    pair<edge_t*, edge_t*> p = add_edge_pair(e2->v, e1,
                                             e1->v, e2);
    edge_t *&ne1 = p.first, *&ne2 = p.second;

    //split the edge cycle
    edge_t *ne2__pre = ne2->pre;
    ne2->pre = ne1->pre; ne1->pre->nxt = ne2;
    ne1->pre = ne2__pre; ne2__pre->nxt = ne1;
    
    //update hosting face and loop of new edge cycle
    face_t *f = new_face();
    
    loop_t *nl = f->new_loop();
    edge_t *e = ne1;
    do
    {
      e->l = nl;
    }
    while( (e = e->nxt) != ne1 );

    // set both half  edges as first in the cycle.
    ne1->l->e = ne1;
    ne2->l->e = ne2;
    
    solid_t::assert_consistent_B_rep();
    return nl;
  }


}//end namespace euler

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