341 lines
11 KiB
C++
341 lines
11 KiB
C++
// Boost.Geometry (aka GGL, Generic Geometry Library)
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// Copyright (c) 2015 Barend Gehrels, Amsterdam, the Netherlands.
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// This file was modified by Oracle on 2017-2021.
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// Modifications copyright (c) 2017-2021 Oracle and/or its affiliates.
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// Contributed and/or modified by Adam Wulkiewicz, on behalf of Oracle
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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_ALGORITHMS_IS_CONVEX_HPP
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#define BOOST_GEOMETRY_ALGORITHMS_IS_CONVEX_HPP
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#include <boost/range/empty.hpp>
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#include <boost/geometry/algorithms/detail/equals/point_point.hpp>
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#include <boost/geometry/algorithms/detail/dummy_geometries.hpp>
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#include <boost/geometry/algorithms/detail/visit.hpp>
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#include <boost/geometry/core/access.hpp>
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#include <boost/geometry/core/closure.hpp>
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#include <boost/geometry/core/cs.hpp>
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#include <boost/geometry/core/coordinate_dimension.hpp>
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#include <boost/geometry/core/exterior_ring.hpp>
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#include <boost/geometry/core/point_type.hpp>
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#include <boost/geometry/core/interior_rings.hpp>
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#include <boost/geometry/core/visit.hpp>
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#include <boost/geometry/geometries/adapted/boost_variant.hpp> // For backward compatibility
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#include <boost/geometry/geometries/concepts/check.hpp>
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#include <boost/geometry/iterators/ever_circling_iterator.hpp>
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#include <boost/geometry/strategies/default_strategy.hpp>
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#include <boost/geometry/strategies/is_convex/cartesian.hpp>
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#include <boost/geometry/strategies/is_convex/geographic.hpp>
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#include <boost/geometry/strategies/is_convex/spherical.hpp>
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#include <boost/geometry/views/detail/closed_clockwise_view.hpp>
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namespace boost { namespace geometry
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{
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#ifndef DOXYGEN_NO_DETAIL
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namespace detail { namespace is_convex
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{
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struct ring_is_convex
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{
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template <typename Ring, typename Strategies>
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static inline bool apply(Ring const& ring, Strategies const& strategies)
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{
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std::size_t n = boost::size(ring);
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if (n < detail::minimum_ring_size<Ring>::value)
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{
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// (Too) small rings are considered as non-concave, is convex
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return true;
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}
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// Walk in clockwise direction, consider ring as closed
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// (though closure is not important in this algorithm - any dupped
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// point is skipped)
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using view_type = detail::closed_clockwise_view<Ring const>;
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view_type const view(ring);
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using it_type = geometry::ever_circling_range_iterator<view_type const>;
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it_type previous(view);
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it_type current(view);
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current++;
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auto const equals_strategy = strategies.relate(dummy_point(), dummy_point());
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std::size_t index = 1;
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while (equals::equals_point_point(*current, *previous, equals_strategy)
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&& index < n)
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{
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current++;
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index++;
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}
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if (index == n)
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{
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// All points are apparently equal
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return true;
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}
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it_type next = current;
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next++;
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while (equals::equals_point_point(*current, *next, equals_strategy))
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{
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next++;
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}
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auto const side_strategy = strategies.side();
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// We have now three different points on the ring
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// Walk through all points, use a counter because of the ever-circling
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// iterator
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for (std::size_t i = 0; i < n; i++)
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{
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int const side = side_strategy.apply(*previous, *current, *next);
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if (side == 1)
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{
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// Next is on the left side of clockwise ring:
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// the piece is not convex
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return false;
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}
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previous = current;
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current = next;
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// Advance next to next different point
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// (because there are non-equal points, this loop is not infinite)
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next++;
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while (equals::equals_point_point(*current, *next, equals_strategy))
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{
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next++;
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}
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}
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return true;
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}
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};
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struct polygon_is_convex
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{
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template <typename Polygon, typename Strategies>
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static inline bool apply(Polygon const& polygon, Strategies const& strategies)
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{
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return boost::empty(interior_rings(polygon))
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&& ring_is_convex::apply(exterior_ring(polygon), strategies);
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}
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};
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struct multi_polygon_is_convex
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{
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template <typename MultiPolygon, typename Strategies>
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static inline bool apply(MultiPolygon const& multi_polygon, Strategies const& strategies)
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{
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auto const size = boost::size(multi_polygon);
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return size == 0 // For consistency with ring_is_convex
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|| (size == 1 && polygon_is_convex::apply(range::front(multi_polygon), strategies));
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}
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};
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}} // namespace detail::is_convex
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#endif // DOXYGEN_NO_DETAIL
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#ifndef DOXYGEN_NO_DISPATCH
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namespace dispatch
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{
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template
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<
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typename Geometry,
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typename Tag = typename tag<Geometry>::type
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>
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struct is_convex
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{
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template <typename Strategies>
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static inline bool apply(Geometry const&, Strategies const&)
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{
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// Convexity is not defined for PointLike and Linear geometries.
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// We could implement this because the following definitions would work:
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// - no line segment between two points on the interior or boundary ever goes outside.
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// - convex_hull of geometry is equal to the original geometry, this implies equal
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// topological dimension.
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// For MultiPoint we'd have to check whether or not an arbitrary number of equal points
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// is stored.
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// MultiPolygon we'd have to check for continuous chain of Linestrings which would require
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// the use of relate(pt, seg) or distance(pt, pt) strategy.
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return false;
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}
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};
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template <typename Box>
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struct is_convex<Box, box_tag>
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{
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template <typename Strategies>
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static inline bool apply(Box const& , Strategies const& )
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{
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// Any box is convex (TODO: consider spherical boxes)
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// TODO: in spherical and geographic the answer would be "false" most of the time.
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// Assuming that:
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// - it even makes sense to consider Box in spherical and geographic in this context
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// because it's not a Polygon, e.g. it can degenerate to a Point.
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// - line segments are defined by geodesics and box edges by parallels and meridians
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// - we use this definition: A convex polygon is a simple polygon (not self-intersecting)
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// in which no line segment between two points on the boundary ever goes outside the
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// polygon.
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// Then a geodesic segment would go into the exterior of a Box for all horizontal edges
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// of a Box unless it was one of the poles (edge degenerated to a point) or equator and
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// longitude difference was lesser than 360 (otherwise depending on the CS there would be
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// no solution or there would be two possible solutions - segment going through one of
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// the poles, at least in case of oblate spheroid, either way the answer would probably
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// be "false").
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return true;
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}
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};
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template <typename Ring>
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struct is_convex<Ring, ring_tag> : detail::is_convex::ring_is_convex
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{};
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template <typename Polygon>
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struct is_convex<Polygon, polygon_tag> : detail::is_convex::polygon_is_convex
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{};
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template <typename MultiPolygon>
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struct is_convex<MultiPolygon, multi_polygon_tag> : detail::is_convex::multi_polygon_is_convex
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{};
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} // namespace dispatch
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#endif // DOXYGEN_NO_DISPATCH
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namespace resolve_strategy {
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template
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<
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typename Strategies,
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bool IsUmbrella = strategies::detail::is_umbrella_strategy<Strategies>::value
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>
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struct is_convex
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{
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template <typename Geometry>
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static bool apply(Geometry const& geometry, Strategies const& strategies)
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{
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return dispatch::is_convex<Geometry>::apply(geometry, strategies);
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}
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};
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template <typename Strategy>
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struct is_convex<Strategy, false>
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{
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template <typename Geometry>
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static bool apply(Geometry const& geometry, Strategy const& strategy)
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{
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using strategies::is_convex::services::strategy_converter;
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return dispatch::is_convex
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<
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Geometry
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>::apply(geometry, strategy_converter<Strategy>::get(strategy));
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}
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};
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template <>
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struct is_convex<default_strategy, false>
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{
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template <typename Geometry>
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static bool apply(Geometry const& geometry, default_strategy const& )
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{
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typedef typename strategies::is_convex::services::default_strategy
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<
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Geometry
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>::type strategy_type;
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return dispatch::is_convex<Geometry>::apply(geometry, strategy_type());
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}
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};
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} // namespace resolve_strategy
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namespace resolve_dynamic {
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template <typename Geometry, typename Tag = typename tag<Geometry>::type>
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struct is_convex
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{
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template <typename Strategy>
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static bool apply(Geometry const& geometry, Strategy const& strategy)
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{
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concepts::check<Geometry>();
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return resolve_strategy::is_convex<Strategy>::apply(geometry, strategy);
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}
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};
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template <typename Geometry>
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struct is_convex<Geometry, dynamic_geometry_tag>
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{
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template <typename Strategy>
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static inline bool apply(Geometry const& geometry, Strategy const& strategy)
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{
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bool result = false;
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traits::visit<Geometry>::apply([&](auto const& g)
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{
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result = is_convex<util::remove_cref_t<decltype(g)>>::apply(g, strategy);
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}, geometry);
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return result;
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}
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};
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// NOTE: This is a simple implementation checking if a GC contains single convex geometry.
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// Technically a GC could store e.g. polygons touching with edges and together creating a convex
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// region. To check this we'd require relate() strategy and the algorithm would be quite complex.
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template <typename Geometry>
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struct is_convex<Geometry, geometry_collection_tag>
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{
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template <typename Strategy>
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static inline bool apply(Geometry const& geometry, Strategy const& strategy)
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{
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bool result = false;
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bool is_first = true;
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detail::visit_breadth_first([&](auto const& g)
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{
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result = is_first
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&& is_convex<util::remove_cref_t<decltype(g)>>::apply(g, strategy);
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is_first = false;
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return result;
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}, geometry);
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return result;
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}
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};
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} // namespace resolve_dynamic
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// TODO: documentation / qbk
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template<typename Geometry>
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inline bool is_convex(Geometry const& geometry)
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{
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return resolve_dynamic::is_convex
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<
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Geometry
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>::apply(geometry, geometry::default_strategy());
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}
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// TODO: documentation / qbk
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template<typename Geometry, typename Strategy>
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inline bool is_convex(Geometry const& geometry, Strategy const& strategy)
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{
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return resolve_dynamic::is_convex<Geometry>::apply(geometry, strategy);
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}
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}} // namespace boost::geometry
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#endif // BOOST_GEOMETRY_ALGORITHMS_IS_CONVEX_HPP
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