// Boost.Geometry (aka GGL, Generic Geometry Library)
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// Copyright (c) 2007-2012 Barend Gehrels, Amsterdam, the Netherlands.
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// This file was modified by Oracle on 2014-2020.
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// Modifications copyright (c) 2014-2020 Oracle and/or its affiliates.
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// Contributed and/or modified by Adam Wulkiewicz, on behalf of Oracle
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// Parts of Boost.Geometry are redesigned from Geodan's Geographic Library
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// (geolib/GGL), copyright (c) 1995-2010 Geodan, Amsterdam, the Netherlands.
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// Use, modification and distribution is subject to the Boost Software License,
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// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_GEOMETRY_STRATEGIES_AGNOSTIC_CONVEX_GRAHAM_ANDREW_HPP
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#define BOOST_GEOMETRY_STRATEGIES_AGNOSTIC_CONVEX_GRAHAM_ANDREW_HPP
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#include <cstddef>
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#include <algorithm>
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#include <vector>
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#include <boost/range/begin.hpp>
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#include <boost/range/empty.hpp>
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#include <boost/range/end.hpp>
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#include <boost/range/size.hpp>
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#include <boost/geometry/algorithms/detail/for_each_range.hpp>
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#include <boost/geometry/core/assert.hpp>
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#include <boost/geometry/core/cs.hpp>
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#include <boost/geometry/core/point_type.hpp>
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#include <boost/geometry/policies/compare.hpp>
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#include <boost/geometry/strategies/convex_hull.hpp>
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#include <boost/geometry/strategies/side.hpp>
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#include <boost/geometry/views/detail/range_type.hpp>
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namespace boost { namespace geometry
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{
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namespace strategy { namespace convex_hull
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{
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#ifndef DOXYGEN_NO_DETAIL
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namespace detail
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{
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template <typename Geometry, typename Point, typename Less>
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inline void get_extremes(Geometry const& geometry,
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Point& left, Point& right,
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Less const& less)
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{
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bool first = true;
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geometry::detail::for_each_range(geometry, [&](auto const& range)
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{
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if (boost::empty(range))
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{
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return;
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}
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// First iterate through this range
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// (this two-stage approach avoids many point copies,
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// because iterators are kept in memory. Because iterators are
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// not persistent (in MSVC) this approach is not applicable
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// for more ranges together)
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auto left_it = boost::begin(range);
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auto right_it = boost::begin(range);
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for (auto it = ++boost::begin(range); it != boost::end(range); ++it)
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{
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if (less(*it, *left_it))
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{
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left_it = it;
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}
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if (less(*right_it, *it))
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{
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right_it = it;
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}
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}
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// Then compare with earlier
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if (first)
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{
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// First time, assign left/right
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left = *left_it;
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right = *right_it;
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first = false;
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}
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else
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{
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// Next time, check if this range was left/right from
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// the extremes already collected
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if (less(*left_it, left))
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{
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left = *left_it;
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}
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if (less(right, *right_it))
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{
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right = *right_it;
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}
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}
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});
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}
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template
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<
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typename Geometry,
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typename Point,
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typename Container,
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typename SideStrategy
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>
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inline void assign_ranges(Geometry const& geometry,
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Point const& most_left, Point const& most_right,
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Container& lower_points, Container& upper_points,
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SideStrategy const& side)
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{
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geometry::detail::for_each_range(geometry, [&](auto const& range)
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{
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// Put points in one of the two output sequences
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for (auto it = boost::begin(range); it != boost::end(range); ++it)
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{
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// check if it is lying most_left or most_right from the line
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int dir = side.apply(most_left, most_right, *it);
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switch(dir)
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{
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case 1 : // left side
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upper_points.push_back(*it);
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break;
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case -1 : // right side
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lower_points.push_back(*it);
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break;
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// 0: on line most_left-most_right,
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// or most_left, or most_right,
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// -> all never part of hull
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}
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}
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});
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}
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template <typename Range, typename Less>
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inline void sort(Range& range, Less const& less)
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{
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std::sort(boost::begin(range), boost::end(range), less);
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}
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} // namespace detail
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#endif // DOXYGEN_NO_DETAIL
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/*!
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\brief Graham scan strategy to calculate convex hull
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\ingroup strategies
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*/
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template <typename InputGeometry, typename OutputPoint>
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class graham_andrew
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{
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public :
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typedef OutputPoint point_type;
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typedef InputGeometry geometry_type;
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private:
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typedef typename cs_tag<point_type>::type cs_tag;
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typedef typename std::vector<point_type> container_type;
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typedef typename std::vector<point_type>::const_iterator iterator;
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typedef typename std::vector<point_type>::const_reverse_iterator rev_iterator;
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class partitions
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{
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friend class graham_andrew;
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container_type m_lower_hull;
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container_type m_upper_hull;
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container_type m_copied_input;
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};
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public:
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typedef partitions state_type;
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inline void apply(InputGeometry const& geometry, partitions& state) const
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{
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// First pass.
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// Get min/max (in most cases left / right) points
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// This makes use of the geometry::less/greater predicates
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// For the left boundary it is important that multiple points
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// are sorted from bottom to top. Therefore the less predicate
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// does not take the x-only template parameter (this fixes ticket #6019.
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// For the right boundary it is not necessary (though also not harmful),
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// because points are sorted from bottom to top in a later stage.
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// For symmetry and to get often more balanced lower/upper halves
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// we keep it.
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typedef typename geometry::point_type<InputGeometry>::type point_type;
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point_type most_left, most_right;
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// TODO: User-defined CS-specific less-compare
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geometry::less<point_type> less;
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detail::get_extremes(geometry, most_left, most_right, less);
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container_type lower_points, upper_points;
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// TODO: User-defiend CS-specific side strategy
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typename strategy::side::services::default_strategy<cs_tag>::type side;
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// Bounding left/right points
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// Second pass, now that extremes are found, assign all points
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// in either lower, either upper
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detail::assign_ranges(geometry, most_left, most_right,
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lower_points, upper_points,
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side);
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// Sort both collections, first on x(, then on y)
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detail::sort(lower_points, less);
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detail::sort(upper_points, less);
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// And decide which point should be in the final hull
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build_half_hull<-1>(lower_points, state.m_lower_hull,
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most_left, most_right,
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side);
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build_half_hull<1>(upper_points, state.m_upper_hull,
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most_left, most_right,
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side);
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}
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template <typename OutputIterator>
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inline void result(partitions const& state,
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OutputIterator out,
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bool clockwise,
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bool closed) const
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{
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if (clockwise)
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{
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output_ranges(state.m_upper_hull, state.m_lower_hull, out, closed);
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}
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else
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{
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output_ranges(state.m_lower_hull, state.m_upper_hull, out, closed);
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}
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}
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private:
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template <int Factor, typename SideStrategy>
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static inline void build_half_hull(container_type const& input,
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container_type& output,
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point_type const& left, point_type const& right,
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SideStrategy const& side)
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{
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output.push_back(left);
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for(iterator it = input.begin(); it != input.end(); ++it)
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{
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add_to_hull<Factor>(*it, output, side);
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}
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add_to_hull<Factor>(right, output, side);
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}
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template <int Factor, typename SideStrategy>
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static inline void add_to_hull(point_type const& p, container_type& output,
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SideStrategy const& side)
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{
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output.push_back(p);
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std::size_t output_size = output.size();
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while (output_size >= 3)
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{
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rev_iterator rit = output.rbegin();
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point_type const last = *rit++;
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point_type const& last2 = *rit++;
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if (Factor * side.apply(*rit, last, last2) <= 0)
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{
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// Remove last two points from stack, and add last again
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// This is much faster then erasing the one but last.
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output.pop_back();
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output.pop_back();
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output.push_back(last);
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output_size--;
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}
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else
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{
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return;
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}
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}
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}
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template <typename OutputIterator>
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static inline void output_ranges(container_type const& first, container_type const& second,
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OutputIterator out, bool closed)
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{
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std::copy(boost::begin(first), boost::end(first), out);
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BOOST_GEOMETRY_ASSERT(closed ? !boost::empty(second) : boost::size(second) > 1);
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std::copy(++boost::rbegin(second), // skip the first Point
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closed ? boost::rend(second) : --boost::rend(second), // skip the last Point if open
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out);
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typedef typename boost::range_size<container_type>::type size_type;
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size_type const count = boost::size(first) + boost::size(second) - 1;
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// count describes a closed case but comparison with min size of closed
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// gives the result compatible also with open
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// here core_detail::closure::minimum_ring_size<closed> could be used
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if (count < 4)
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{
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// there should be only one missing
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*out++ = *boost::begin(first);
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}
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}
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};
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}} // namespace strategy::convex_hull
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#ifndef DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
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template <typename InputGeometry, typename OutputPoint>
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struct strategy_convex_hull<InputGeometry, OutputPoint, cartesian_tag>
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{
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typedef strategy::convex_hull::graham_andrew<InputGeometry, OutputPoint> type;
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};
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#endif
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}} // namespace boost::geometry
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#endif // BOOST_GEOMETRY_STRATEGIES_AGNOSTIC_CONVEX_GRAHAM_ANDREW_HPP
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