[algorithms][is_valid] implement predicate class that determines

whether a polygon or multi-polygon turn is acceptable (code partially
moved from algorithms/detail/is_valid/polygon.hpp)

include/boost/geometry/algorithms/detail/is_valid/is_acceptable_turn.hpp

@@ -0,0 +1,144 @@
+// Boost.Geometry (aka GGL, Generic Geometry Library)
+
+// Copyright (c) 2014, Oracle and/or its affiliates.
+
+// Contributed and/or modified by Menelaos Karavelas, on behalf of Oracle
+
+// Licensed under the Boost Software License version 1.0.
+// http://www.boost.org/users/license.html
+
+#ifndef BOOST_GEOMETRY_ALGORITHMS_DETAIL_IS_VALID_IS_ACCEPTABLE_TURN_HPP
+#define BOOST_GEOMETRY_ALGORITHMS_DETAIL_IS_VALID_IS_ACCEPTABLE_TURN_HPP
+
+#include <boost/range.hpp>
+
+#include <boost/geometry/core/point_order.hpp>
+#include <boost/geometry/core/tag.hpp>
+#include <boost/geometry/core/tags.hpp>
+
+#include <boost/geometry/algorithms/detail/overlay/turn_info.hpp>
+
+
+namespace boost { namespace geometry
+{
+
+
+#ifndef DOXYGEN_NO_DETAIL
+namespace detail { namespace is_valid
+{
+
+
+template
+<
+    typename Geometry,
+    order_selector Order = geometry::point_order<Geometry>::value,
+    typename Tag = typename tag<Geometry>::type
+>
+struct acceptable_operation
+{};
+
+template <typename Polygon>
+struct acceptable_operation<Polygon, counterclockwise, polygon_tag>
+{
+    static const detail::overlay::operation_type value =
+        detail::overlay::operation_union;
+};
+
+template <typename Polygon>
+struct acceptable_operation<Polygon, clockwise, polygon_tag>
+{
+    static const detail::overlay::operation_type value =
+        detail::overlay::operation_intersection;
+};
+
+template <typename MultiPolygon>
+struct acceptable_operation<MultiPolygon, counterclockwise, multi_polygon_tag>
+{
+    static const detail::overlay::operation_type value =
+        detail::overlay::operation_intersection;
+};
+
+template <typename MultiPolygon>
+struct acceptable_operation<MultiPolygon, clockwise, multi_polygon_tag>
+{
+    static const detail::overlay::operation_type value =
+        detail::overlay::operation_union;
+};
+
+
+
+
+template <typename Geometry, typename Tag = typename tag<Geometry>::type>
+struct is_acceptable_turn
+{};
+
+template <typename Polygon>
+class is_acceptable_turn<Polygon, polygon_tag>
+{
+protected:
+    template <typename Turn, typename Method, typename Operation>
+    static inline bool check_turn(Turn const& turn,
+                                  Method method,
+                                  Operation operation)
+    {
+        return turn.method == method
+            && turn.operations[0].operation == operation
+            && turn.operations[1].operation == operation;
+    }
+
+
+public:
+    template <typename Turn>
+    static inline bool apply(Turn const& turn)
+    {
+        using namespace detail::overlay;
+
+        if ( turn.operations[0].seg_id.ring_index
+             == turn.operations[0].other_id.ring_index )
+        {
+            return false;
+        }
+
+        operation_type const op = acceptable_operation<Polygon>::value;
+
+        return check_turn(turn, method_touch_interior, op)
+            || check_turn(turn, method_touch, op)
+            ;
+    }
+};
+
+template <typename MultiPolygon>
+class is_acceptable_turn<MultiPolygon, multi_polygon_tag>
+    : is_acceptable_turn<typename boost::range_value<MultiPolygon>::type>
+{
+private:
+    typedef typename boost::range_value<MultiPolygon>::type polygon;
+    typedef is_acceptable_turn<polygon> base;
+
+public:
+    template <typename Turn>
+    static inline bool apply(Turn const& turn)
+    {
+        using namespace detail::overlay;
+
+        if ( turn.operations[0].seg_id.multi_index
+             == turn.operations[0].other_id.multi_index )
+        {
+            return base::apply(turn);
+        }
+
+        operation_type const op = acceptable_operation<MultiPolygon>::value;
+
+        return base::check_turn(turn, method_touch_interior, op)
+            || base::check_turn(turn, method_touch, op)
+            ;
+    }
+};   
+
+
+}} // namespace detail::is_valid
+#endif // DOXYGEN_NO_DETAIL
+
+}} // namespace boost::geometry
+
+#endif // BOOST_GEOMETRY_ALGORITHMS_DETAIL_IS_VALID_IS_ACCEPTABLE_TURN_HPP