# [Boost-bugs] [Boost C++ Libraries] #6366: Bug in "boost::polygon::contains" for polygon_90 type

Subject: [Boost-bugs] [Boost C++ Libraries] #6366: Bug in "boost::polygon::contains" for polygon_90 type
Date: 2012-01-07 15:24:55

#6366: Bug in "boost::polygon::contains" for polygon_90 type
-----------------------------------------+----------------------------------
Reporter: sebastien.mirabel@â€¦ | Owner: ljsimons
Type: Bugs | Status: new
Milestone: To Be Determined | Component: polygon
Version: Boost 1.48.0 | Severity: Problem
Keywords: |
-----------------------------------------+----------------------------------
For a polygon ((0,0) (10,0) (10,10) (0,10)) the function "contains"
returns true for (15,5) whereas it should return true

{{{
#include <boost/polygon/polygon.hpp>

#include <cassert>
#include <iostream>

namespace gtl = boost::polygon;
using namespace boost::polygon::operators;

int main() {
//lets construct a 10x10 rectangle shaped polygon
typedef gtl::polygon_90_data<int> Polygon;
typedef gtl::polygon_traits_90<Polygon>::point_type Point;
Point pts[] = {
gtl::construct<Point>(0, 0),
gtl::construct<Point>(10, 0),
gtl::construct<Point>(10, 10),
gtl::construct<Point>(0, 10)};
Polygon poly;
gtl::set_points(poly, pts, pts+4);

Point point = gtl::construct<Point>(15, 5);
{
// Wrong result here :
bool result = gtl::contains(poly, point);
std::cout << std::boolalpha << result << std::endl;
}
//assert(!gtl::contains(poly, point));
//assert(!gtl::contains(poly, gtl::construct<Point>(15, 5)));
return 0;
}

}}}

The bugs seems to come from line 1176 of
"boost\polygon\polygon_traits.hpp" :
{{{
//an odd number of edges to the left implies interior pt
return counts[winding(polygon) == COUNTERCLOCKWISE ? 0 : 1] % 4 != 0;
}}}

There is "% 4" whereas the previous comment indicate "an odd number of
edges" (this logicaly should be "% 2")

```--
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6366>
Boost C++ Libraries <http://www.boost.org/>
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```

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