[dissolve] introduce Reverse to be able to (later) apply dissolve in two directions,

not only to support cw/ccw, but more to only use one version (positive area)
instead of processing cw input which is effectively ccw.

extensions/test/algorithms/dissolve.cpp

@@ -387,10 +387,9 @@ void test_dissolve(std::string const& caseid, Geometry const& geometry,
 
         bg::dispatch::dissolve
             <
-                typename bg::tag<Geometry>::type,
-                typename bg::tag<GeometryOut>::type,
                 Geometry,
-                GeometryOut
+                GeometryOut,
+                false
             >::apply(geometry, robust_policy, std::back_inserter(dissolved1),
                      strategy, visitor);
 

include/boost/geometry/extensions/algorithms/detail/overlay/dissolve_traverse.hpp

@@ -28,7 +28,7 @@ namespace detail { namespace dissolve
         for dissolves calls traversal_ring_creator in two phases
     \ingroup dissolve
  */
-template <typename Backtrack>
+template <bool Reverse, typename Backtrack>
 class traverse
 {
 
@@ -54,7 +54,7 @@ public :
     {
         detail::overlay::traversal_ring_creator
             <
-                false, false, overlay_dissolve,
+                Reverse, Reverse, overlay_dissolve,
                 Geometry, Geometry,
                 Turns, TurnInfoMap, Clusters,
                 IntersectionStrategy,

include/boost/geometry/extensions/algorithms/dissolve.hpp

@@ -113,7 +113,7 @@ public :
     }
 };
 
-template <typename Geometry, typename GeometryOut>
+template <typename Geometry, typename GeometryOut, bool Reverse>
 struct dissolve_ring_or_polygon
 {
     template <typename Turns>
@@ -169,8 +169,9 @@ struct dissolve_ring_or_polygon
 
         std::vector<turn_info> turns;
         detail::dissolve::no_interrupt_policy policy;
-        geometry::self_turns
+        detail::self_get_turn_points::self_turns
             <
+                Reverse,
                 detail::overlay::assign_null_policy
             >(geometry, strategy, rescale_policy, turns, policy, 0, false);
 
@@ -205,7 +206,7 @@ struct dissolve_ring_or_polygon
         typename Strategy::side_strategy_type const
             side_strategy = strategy.get_side_strategy();
 
-        enrich_intersection_points<false, false, overlay_dissolve>(turns,
+        enrich_intersection_points<Reverse, Reverse, overlay_dissolve>(turns,
                     clusters, geometry, geometry, rescale_policy,
                     side_strategy);
 
@@ -215,7 +216,7 @@ struct dissolve_ring_or_polygon
 
         std::map<ring_identifier, overlay::ring_turn_info> turn_info_per_ring;
 
-        detail::dissolve::traverse<backtrack_for_dissolve<Geometry> >
+        detail::dissolve::traverse<Reverse, backtrack_for_dissolve<Geometry> >
                 ::apply(geometry, strategy, rescale_policy,
                      turns, rings, turn_info_per_ring, clusters, visitor);
 
@@ -297,25 +298,26 @@ namespace dispatch
 
 template
 <
-    typename GeometryTag,
-    typename GeometryOutTag,
     typename Geometry,
-    typename GeometryOut
+    typename GeometryOut,
+    bool Reverse,
+    typename GeometryTag = typename tag<Geometry>::type,
+    typename GeometryOutTag = typename tag<GeometryOut>::type
 >
 struct dissolve
     : not_implemented<GeometryTag, GeometryOutTag>
 {};
 
 
-template<typename Polygon, typename PolygonOut>
-struct dissolve<polygon_tag, polygon_tag, Polygon, PolygonOut>
-    : detail::dissolve::dissolve_ring_or_polygon<Polygon, PolygonOut>
+template<typename Polygon, typename PolygonOut, bool Reverse>
+struct dissolve<Polygon, PolygonOut, Reverse, polygon_tag, polygon_tag>
+    : detail::dissolve::dissolve_ring_or_polygon<Polygon, PolygonOut, Reverse>
 {};
 
 
-template<typename Ring, typename RingOut>
-struct dissolve<ring_tag, ring_tag, Ring, RingOut>
-    : detail::dissolve::dissolve_ring_or_polygon<Ring, RingOut>
+template<typename Ring, typename RingOut, bool Reverse>
+struct dissolve<Ring, RingOut, Reverse, ring_tag, ring_tag>
+    : detail::dissolve::dissolve_ring_or_polygon<Ring, RingOut, Reverse>
 {};
 
 
@@ -365,10 +367,12 @@ inline OutputIterator dissolve_inserter(Geometry const& geometry,
 
     return dispatch::dissolve
     <
-        typename tag<Geometry>::type,
-        typename tag<GeometryOut>::type,
         Geometry,
-        GeometryOut
+        GeometryOut,
+        detail::overlay::do_reverse
+        <
+            geometry::point_order<Geometry>::value
+        >::value
     >::apply(geometry, robust_policy, out, strategy, visitor);
 }
 
@@ -430,10 +434,12 @@ inline void dissolve(Geometry const& geometry, Collection& output_collection,
 
     dispatch::dissolve
     <
-        typename tag<Geometry>::type,
-        typename tag<geometry_out>::type,
         Geometry,
-        geometry_out
+        geometry_out,
+        detail::overlay::do_reverse
+        <
+            geometry::point_order<Geometry>::value
+        >::value
     >::apply(geometry, robust_policy,
              std::back_inserter(output_collection),
              strategy, visitor);

include/boost/geometry/extensions/multi/algorithms/dissolve.hpp

@@ -35,7 +35,7 @@ namespace boost { namespace geometry
 namespace detail { namespace dissolve
 {
 
-template <typename Multi, typename GeometryOut>
+template <typename Multi, typename GeometryOut, bool Reverse>
 struct dissolve_multi
 {
     template
@@ -59,7 +59,8 @@ struct dissolve_multi
             dissolve_ring_or_polygon
                 <
                     polygon_type,
-                    GeometryOut
+                    GeometryOut,
+                    Reverse
                 >::apply(*it, rescale_policy, std::back_inserter(step1),
                          strategy, visitor);
         }
@@ -96,9 +97,9 @@ namespace dispatch
 {
 
 
-template<typename Multi, typename GeometryOut>
-struct dissolve<multi_polygon_tag, polygon_tag, Multi, GeometryOut>
-    : detail::dissolve::dissolve_multi<Multi, GeometryOut>
+template<typename Multi, typename GeometryOut, bool Reverse>
+struct dissolve<Multi, GeometryOut, Reverse, multi_polygon_tag, polygon_tag>
+    : detail::dissolve::dissolve_multi<Multi, GeometryOut, Reverse>
 {};