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// Copyright (c) 2006 Fernando Luis Cacciola Carballal. All rights reserved.
//
// This file is part of CGAL (www.cgal.org); you may redistribute it under
// the terms of the Q Public License version 1.0.
// See the file LICENSE.QPL distributed with CGAL.
//
// Licensees holding a valid commercial license may use this file in
// accordance with the commercial license agreement provided with the software.
//
// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
//
// $URL: svn+ssh://scm.gforge.inria.fr/svn/cgal/branches/CGAL-3.5-branch/Straight_skeleton_2/include/CGAL/constructions/Polygon_offset_cons_ftC2.h $
// $Id: Polygon_offset_cons_ftC2.h 46517 2008-10-28 13:35:18Z afabri $
//
// Author(s) : Fernando Cacciola <fernando_cacciola@ciudad.com.ar>
//
#ifndef CGAL_POLYGON_OFFSET_CONS_FTC2_H
#define CGAL_POLYGON_OFFSET_CONS_FTC2_H 1
#include <CGAL/constructions/Straight_skeleton_cons_ftC2.h>
CGAL_BEGIN_NAMESPACE
namespace CGAL_SS_i
{
// Given an offset distance 't' and 2 oriented line segments e0 and e1, returns the coordinates (x,y)
// of the intersection of their offsets at the given distance.
//
// PRECONDITIONS:
// The line coefficients must be normalized: a�+b�==1 and (a,b) being the leftward normal vector
// The offsets at the given distance do intersect in a single point.
//
// POSTCONDITION: In case of overflow an empty optional is returned.
//
template<class K>
optional< Point_2<K> > construct_offset_pointC2 ( typename K::FT const& t
, Segment_2<K> const& e0
, Segment_2<K> const& e1
, intrusive_ptr< Trisegment_2<K> > const& tri
)
{
typedef typename K::FT FT ;
typedef Point_2<K> Point_2 ;
typedef Line_2<K> Line_2 ;
typedef optional<Point_2> Optional_point_2 ;
typedef optional<Line_2> Optional_line_2 ;
FT x(0.0),y(0.0) ;
CGAL_STSKEL_TRAITS_TRACE("Constructing offset point for t=" << t << " e0=" << s2str(e0) << " e1=" << s2str(e1) << " tri=" << tri ) ;
Optional_line_2 l0 = compute_normalized_line_ceoffC2(e0) ;
Optional_line_2 l1 = compute_normalized_line_ceoffC2(e1) ;
bool ok = false ;
if ( l0 && l1 )
{
FT den = l1->a() * l0->b() - l0->a() * l1->b() ;
if ( CGAL_NTS is_finite(den) )
{
if ( ! CGAL_NTS is_zero(den) )
{
FT numX = t * l1->b() - t * l0->b() + l0->b() * l1->c() - l1->b() * l0->c() ;
FT numY = t * l1->a() - t * l0->a() + l0->a() * l1->c() - l1->a() * l0->c() ;
x = -numX / den ;
y = numY / den ;
ok = CGAL_NTS is_finite(x) && CGAL_NTS is_finite(y) ;
}
else
{
CGAL_STSKEL_TRAITS_TRACE(" DEGENERATE case: Collinear segments involved. Seed event " << ( !tri ? " ABSENT" : " exists." ) ) ;
Optional_point_2 q = tri ? construct_offset_lines_isecC2(tri) : compute_oriented_midpoint(e0,e1) ;
if ( q )
{
CGAL_STSKEL_TRAITS_TRACE(" Seed point: " << p2str(*q) ) ;
FT px, py ;
line_project_pointC2(l0->a(),l0->b(),l0->c(),q->x(),q->y(),px,py);
CGAL_STSKEL_TRAITS_TRACE(" Projected seed point: (" << px << "," << py << ")" ) ;
x = px + l0->a() * t ;
y = py + l0->b() * t ;
ok = CGAL_NTS is_finite(x) && CGAL_NTS is_finite(y) ;
}
}
}
}
CGAL_STSKEL_TRAITS_TRACE(" RESULT: (" << x << "," << y << ")" << ( ok ? "" : " NONE really" ) ) ;
return cgal_make_optional(ok,K().construct_point_2_object()(x,y)) ;
}
} // namespace CGAL_SS_i
CGAL_END_NAMESPACE
#endif // CGAL_POLYGON_OFFSET_CONS_FTC2_H //
// EOF //
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