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[algorithms][intersection] Fixes liang_barsky for integer coordinate types

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- Fixes an integer division bug which caused incorrect clipping results when
   a geometry is clipped by a box and the coordinate type is integral
 - Refs https://github.com/mapbox/mapnik-vector-tile/pull/102
This commit is contained in:
Dane Springmeyer
2015-10-06 13:58:18 -07:00
parent b3be70aee2
commit eb7613e703
1 changed files with 7 additions and 6 deletions
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13
include/boost/geometry/algorithms/detail/overlay/clip_linestring.hpp
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@@ -51,14 +51,14 @@ class liang_barsky
private:
typedef model::referring_segment<Point> segment_type;
template <typename T>
inline bool check_edge(T const& p, T const& q, T& t1, T& t2) const
template <typename PointType, typename CalcType>
inline bool check_edge(PointType const& p, PointType const& q, CalcType& t1, CalcType& t2) const
{
bool visible = true;
if(p < 0)
{
T const r = q / p;
CalcType const r = static_cast<CalcType>(q) / p;
if (r > t2)
visible = false;
else if (r > t1)
@@ -66,7 +66,7 @@ private:
}
else if(p > 0)
{
T const r = q / p;
CalcType const r = static_cast<CalcType>(q) / p;
if (r < t1)
visible = false;
else if (r < t2)
@@ -86,9 +86,10 @@ public:
inline bool clip_segment(Box const& b, segment_type& s, bool& sp1_clipped, bool& sp2_clipped) const
{
typedef typename select_coordinate_type<Box, Point>::type coordinate_type;
typedef double calc_type;
coordinate_type t1 = 0;
coordinate_type t2 = 1;
calc_type t1 = 0;
calc_type t2 = 1;
coordinate_type const dx = get<1, 0>(s) - get<0, 0>(s);
coordinate_type const dy = get<1, 1>(s) - get<0, 1>(s);