160 lines
6.2 KiB
C
160 lines
6.2 KiB
C
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// Copyright (c) 1997
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// Utrecht University (The Netherlands),
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// ETH Zurich (Switzerland),
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// INRIA Sophia-Antipolis (France),
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// Max-Planck-Institute Saarbruecken (Germany),
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// and Tel-Aviv University (Israel). All rights reserved.
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//
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// This file is part of CGAL (www.cgal.org); you can redistribute it and/or
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// modify it under the terms of the GNU Lesser General Public License as
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// published by the Free Software Foundation; either version 3 of the License,
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// or (at your option) any later version.
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//
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// Licensees holding a valid commercial license may use this file in
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// accordance with the commercial license agreement provided with the software.
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//
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// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
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// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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//
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// $URL$
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// $Id$
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// SPDX-License-Identifier: LGPL-3.0+
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//
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//
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// Author(s) : Lutz Kettner <kettner@mpi-sb.mpg.de>
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// Cuts out a piece of a halfedge data structure defined by a predicate.
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#ifndef CGAL_HALFEDGEDS_CUT_COMPONENT_H
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#define CGAL_HALFEDGEDS_CUT_COMPONENT_H 1
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#include <CGAL/disable_warnings.h>
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#include <CGAL/basic.h>
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#include <CGAL/HalfedgeDS_decorator.h>
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namespace CGAL {
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template < class HDS, class Predicate >
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typename HDS::Halfedge_handle
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halfedgeDS_cut_component( HDS& hds,
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typename HDS::Halfedge_handle h,
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Predicate pred,
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typename HDS::Halfedge_handle& cut_piece)
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// Cuts out a piece of a halfedge data structure for which the predicate
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// `pred' is true for the vertices.
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// The edge-vertex graph of the piece has to be a connected component.
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// The remaining piece gets a new boundary. Returns a border halfedge of
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// the new boundary on the remaining piece. Assigns a halfedge of the
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// cut outpiece to `cut_piece'.
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// The geometry for the vertices
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// on the boundary and the hole have to be taken care of after this
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// function call. The cut-out piece can be deleted with the member
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// function erase_connected_component of the decorator class. It can
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// technically happen that only an isolated vertex would remain in the
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// cut out piece, in which case a dummy halfedge pair and vertex will be
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// created to keep this vertex representable in the halfedge data structure.
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// Precondition: pred( h->vertex()) && ! pred( h->opposite()->vertex()).
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{
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typedef typename HDS::Vertex_handle Vertex_handle;
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typedef typename HDS::Halfedge_handle Halfedge_handle;
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typedef typename HDS::Face_handle Face_handle;
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typedef typename HDS::Vertex Vertex;
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typedef typename HDS::Halfedge Halfedge;
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typedef typename HDS::Face Face;
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CGAL::HalfedgeDS_decorator<HDS> D(hds);
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CGAL_precondition( D.is_valid(false,3));
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CGAL_precondition( pred( h->vertex()));
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CGAL_precondition( ! pred( h->opposite()->vertex()));
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Halfedge_handle start = h;
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Halfedge_handle hnew;
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Halfedge_handle hlast;
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while (true) {
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// search re-entry point
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Halfedge_handle g = h;
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while ( pred( g->next()->vertex())) {
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g = g->next();
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// create border edges around cap
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D.set_face( g, Face_handle());
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}
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if ( hnew == Halfedge_handle()) {
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// first edge, special case
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CGAL_assertion( g->next() != h && g->next()->opposite() != h);
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Halfedge_handle gnext = g->next()->opposite();
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D.remove_tip( g);
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Vertex_handle v = D.vertices_push_back( Vertex());
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D.close_tip( gnext, v);
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hnew = hds.edges_push_back( Halfedge(), Halfedge());
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hlast = hnew->opposite();
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D.insert_tip( hlast, gnext);
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D.set_face( hnew, D.get_face( gnext));
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D.set_face_halfedge( hnew);
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h = g;
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D.set_vertex_halfedge( h);
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} else { // general case and last case
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Halfedge_handle gnext = g->next()->opposite();
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if ( gnext == start && gnext == g) {
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// last edge, special case of isolated vertex.
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// Create dummy edge and dummy vertex and attach it to g
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g = hds.edges_push_back( Halfedge(), Halfedge());
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D.insert_tip( g, gnext);
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D.close_tip(g->opposite(), D.vertices_push_back(Vertex()));
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D.set_vertex_halfedge( g);
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D.set_vertex_halfedge( g->opposite());
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}
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D.remove_tip( g);
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Vertex_handle v = D.vertices_push_back( Vertex());
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D.close_tip( hnew, v);
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D.insert_tip( gnext, hnew);
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hnew = hds.edges_push_back( Halfedge(), Halfedge());
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D.insert_tip( hnew->opposite(), gnext);
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D.set_face( hnew, D.get_face( gnext));
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D.set_face_halfedge( hnew);
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h = g;
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D.set_vertex_halfedge( h);
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if ( gnext == start) {
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// last edge, special
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D.insert_tip( hnew, hlast);
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break;
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}
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}
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} // while(true)
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Face_handle fnew = D.faces_push_back( Face());
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D.set_face_in_face_loop( hlast, fnew);
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D.set_face_halfedge( hlast);
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cut_piece = h;
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CGAL_postcondition( D.is_valid(false,3));
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return hlast;
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}
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template < class HDS, class Predicate >
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typename HDS::Halfedge_handle
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halfedgeDS_cut_component( HDS& hds,
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typename HDS::Halfedge_handle h,
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Predicate pred)
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// Same function as above, but deletes the cut out piece immediately.
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{
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typedef typename HDS::Halfedge_handle Halfedge_handle;
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CGAL::HalfedgeDS_decorator<HDS> D(hds);
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CGAL_precondition( D.is_valid(false,3));
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CGAL_precondition( pred( h->vertex()));
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CGAL_precondition( ! pred( h->opposite()->vertex()));
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Halfedge_handle cut_piece;
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Halfedge_handle hnew = halfedgeDS_cut_component( hds, h, pred, cut_piece);
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D.erase_connected_component( cut_piece);
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CGAL_postcondition( D.is_valid(false,3));
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return hnew;
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}
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} //namespace CGAL
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#include <CGAL/enable_warnings.h>
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#endif // CGAL_HALFEDGEDS_CUT_COMPONENT_H //
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// EOF //
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