boost/boost/geometry/algorithms/detail/point_is_spike_or_equal.hpp

// Boost.Geometry (aka GGL, Generic Geometry Library)

// Copyright (c) 2007-2013 Barend Gehrels, Amsterdam, the Netherlands.
// Copyright (c) 2008-2013 Bruno Lalande, Paris, France.
// Copyright (c) 2009-2013 Mateusz Loskot, London, UK.
// Copyright (c) 2013 Adam Wulkiewicz, Lodz, Poland.

// Use, modification and distribution is subject to the Boost Software License,
// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)

#ifndef BOOST_GEOMETRY_ALGORITHMS_DETAIL_POINT_IS_EQUAL_OR_SPIKE_HPP
#define BOOST_GEOMETRY_ALGORITHMS_DETAIL_POINT_IS_EQUAL_OR_SPIKE_HPP

#include <boost/geometry/arithmetic/arithmetic.hpp>
#include <boost/geometry/algorithms/detail/convert_point_to_point.hpp>
#include <boost/geometry/algorithms/detail/recalculate.hpp>
#include <boost/geometry/policies/robustness/robust_point_type.hpp>
#include <boost/geometry/strategies/side.hpp>
#include <boost/geometry/util/condition.hpp>
#include <boost/geometry/util/math.hpp>

namespace boost { namespace geometry
{


#ifndef DOXYGEN_NO_DETAIL
namespace detail
{

// Checks if a point ("last_point") causes a spike w.r.t.
// the specified two other points (segment_a, segment_b)
//
//  x-------x------x
//  a       lp     b
//
// Above, lp generates a spike w.r.t. segment(a,b)
// So specify last point first, then (a,b) (this is unordered, so unintuitive)
template <typename Point1, typename Point2, typename Point3>
static inline bool point_is_spike_or_equal(Point1 const& last_point,
            Point2 const& segment_a,
            Point3 const& segment_b)
{
    typedef typename strategy::side::services::default_strategy
    <
        typename cs_tag<Point1>::type
    >::type side_strategy;

    typedef Point1 vector_type;

    int const side = side_strategy::apply(last_point, segment_a, segment_b);
    if (side == 0)
    {
        // Last point is collinear w.r.t previous segment.
        // Check if it is equal
        vector_type diff1;
        conversion::convert_point_to_point(last_point, diff1);
        geometry::subtract_point(diff1, segment_b);
        int const sgn_x1 = math::sign(geometry::get<0>(diff1));
        int const sgn_y1 = math::sign(geometry::get<1>(diff1));
        if (sgn_x1 == 0 && sgn_y1 == 0)
        {
            return true;
        }

        // Check if it moves forward
        vector_type diff2;
        conversion::convert_point_to_point(segment_b, diff2);
        geometry::subtract_point(diff2, segment_a);
        int const sgn_x2 = math::sign(geometry::get<0>(diff2));
        int const sgn_y2 = math::sign(geometry::get<1>(diff2));

        return sgn_x1 != sgn_x2 || sgn_y1 != sgn_y2;
    }
    return false;
}

template
<
    typename Point1,
    typename Point2,
    typename Point3,
    typename RobustPolicy
>
static inline bool point_is_spike_or_equal(Point1 const& last_point,
            Point2 const& segment_a,
            Point3 const& segment_b,
            RobustPolicy const& robust_policy)
{
    if (point_is_spike_or_equal(last_point, segment_a, segment_b))
    {
        return true;
    }

    if (BOOST_GEOMETRY_CONDITION(! RobustPolicy::enabled))
    {
        return false;
    }

    // Try using specified robust policy
    typedef typename geometry::robust_point_type
    <
        Point1,
        RobustPolicy
    >::type robust_point_type;

    robust_point_type last_point_rob, segment_a_rob, segment_b_rob;
    geometry::recalculate(last_point_rob, last_point, robust_policy);
    geometry::recalculate(segment_a_rob, segment_a, robust_policy);
    geometry::recalculate(segment_b_rob, segment_b, robust_policy);

    return point_is_spike_or_equal
        (
            last_point_rob,
            segment_a_rob,
            segment_b_rob
        );
}


} // namespace detail
#endif

}} // namespace boost::geometry


#endif // BOOST_GEOMETRY_ALGORITHMS_DETAIL_POINT_IS_EQUAL_OR_SPIKE_HPP