From 3bdefedab16b180841ba5c4b32eaaa494f42d8c8 Mon Sep 17 00:00:00 2001
From: Andrii Sydorchuk <asydorchuk@spotify.com>
Date: Wed, 19 Mar 2014 21:10:09 +0100
Subject: [PATCH] Polygon: fixing reopend issue #6366: defect in polygon 90
 contains.

---
 include/boost/polygon/polygon_traits.hpp | 34 +++++++++++++++++++++++++-------
 1 file changed, 27 insertions(+), 7 deletions(-)

diff --git a/include/boost/polygon/polygon_traits.hpp b/include/boost/polygon/polygon_traits.hpp
index 6055bc7..b03d00f 100644
--- a/include/boost/polygon/polygon_traits.hpp
+++ b/include/boost/polygon/polygon_traits.hpp
@@ -1129,17 +1129,33 @@ namespace boost { namespace polygon{
 
   template <typename T, typename input_point_type>
   typename enable_if<
-    typename gtl_and< typename is_polygon_90_type<T>::type,
-                      typename gtl_same_type<typename geometry_concept<input_point_type>::type, point_concept>::type>::type,
-    bool>::type
-  contains(const T& polygon, const input_point_type& point, bool consider_touch = true) {
+    typename gtl_and<
+      typename is_polygon_90_type<T>::type,
+      typename gtl_same_type<
+        typename geometry_concept<input_point_type>::type,
+        point_concept
+      >::type
+    >::type,
+    bool
+  >::type contains(
+      const T& polygon,
+      const input_point_type& point,
+      bool consider_touch = true) {
     typedef T polygon_type;
     typedef typename polygon_traits<polygon_type>::coordinate_type coordinate_type;
     typedef typename polygon_traits<polygon_type>::iterator_type iterator;
     typedef typename std::iterator_traits<iterator>::value_type point_type;
     coordinate_type point_x = x(point);
     coordinate_type point_y = y(point);
-    bool inside = false;
+    // Check how many intersections has the ray extended from the given
+    // point in the x-axis negative direction with the polygon edges.
+    // If the number is odd the point is within the polygon, otherwise not.
+    // We can safely ignore horizontal edges, however intersections with
+    // end points of the vertical edges require special handling. We should
+    // add one intersection in case horizontal edges that extend vertical edge
+    // point in the same direction.
+    int num_full_intersections = 0;
+    int num_half_intersections = 0;
     for (iterator iter = begin_points(polygon); iter != end_points(polygon);) {
       point_type curr_point = *iter;
       ++iter;
@@ -1154,7 +1170,10 @@ namespace boost { namespace polygon{
           if (x(curr_point) == point_x) {
             return consider_touch;
           }
-          inside ^= true;
+          ++num_full_intersections;
+        }
+        if (point_y == min_y || point_y == max_y) {
+          num_half_intersections += (y(curr_point) < y(next_point) ? 1 : -1);
         }
       } else {
         coordinate_type min_x = (std::min)(x(curr_point), x(next_point));
@@ -1166,7 +1185,8 @@ namespace boost { namespace polygon{
         }
       }
     }
-    return inside;
+    int total_intersections = num_full_intersections + (num_half_intersections >> 1);
+    return total_intersections & 1;
   }
 
   //TODO: refactor to expose as user APIs
-- 
1.8.3.4 (Apple Git-47)