1 files changed, 129 insertions, 0 deletions
diff --git a/src/mbgl/util/geometry_util.cpp b/src/mbgl/util/geometry_util.cpp
new file mode 100644
index 0000000000..df4119ce6a
--- /dev/null
+++ b/src/mbgl/util/geometry_util.cpp
@@ -0,0 +1,129 @@
+#include <mbgl/util/geometry_util.hpp>
+
+#include <algorithm>
+
+namespace mbgl {
+
+template <typename T>
+bool GeometryUtil<T>::rayIntersect(const Point<T>& p, const Point<T>& p1, const Point<T>& p2) {
+    return ((p1.y > p.y) != (p2.y > p.y)) && (p.x < (p2.x - p1.x) * (p.y - p1.y) / (p2.y - p1.y) + p1.x);
+}
+
+// check if point p is on line segment with end points p1 and p2
+template <typename T>
+bool GeometryUtil<T>::pointOnBoundary(const Point<T>& p, const Point<T>& p1, const Point<T>& p2) {
+    // requirements of point p on line segment:
+    // 1. colinear: cross product of vector p->p1(x1, y1) and vector p->p2(x2, y2) equals to 0
+    // 2. p is between p1 and p2
+    const auto x1 = p.x - p1.x;
+    const auto y1 = p.y - p1.y;
+    const auto x2 = p.x - p2.x;
+    const auto y2 = p.y - p2.y;
+    return (x1 * y2 - x2 * y1 == 0) && (x1 * x2 <= 0) && (y1 * y2 <= 0);
+}
+
+template <typename T>
+bool GeometryUtil<T>::segmentIntersectSegment(const Point<T>& a,
+                                              const Point<T>& b,
+                                              const Point<T>& c,
+                                              const Point<T>& d) {
+    // a, b are end points for line segment1, c and d are end points for line segment2
+    const auto perp = [](const Point<T>& v1, const Point<T>& v2) { return (v1.x * v2.y - v1.y * v2.x); };
+
+    // check if two segments are parallel or not
+    // precondition is end point a, b is inside polygon, if line a->b is
+    // parallel to polygon edge c->d, then a->b won't intersect with c->d
+    auto vectorP = Point<T>(b.x - a.x, b.y - a.y);
+    auto vectorQ = Point<T>(d.x - c.x, d.y - c.y);
+    if (perp(vectorQ, vectorP) == 0) return false;
+
+    // check if p1 and p2 are in different sides of line segment q1->q2
+    const auto twoSided = [](const Point<T>& p1, const Point<T>& p2, const Point<T>& q1, const Point<T>& q2) {
+        // q1->p1 (x1, y1), q1->p2 (x2, y2), q1->q2 (x3, y3)
+        T x1 = p1.x - q1.x;
+        T y1 = p1.y - q1.y;
+        T x2 = p2.x - q1.x;
+        T y2 = p2.y - q1.y;
+        T x3 = q2.x - q1.x;
+        T y3 = q2.y - q1.y;
+        auto ret1 = (x1 * y3 - x3 * y1);
+        auto ret2 = (x2 * y3 - x3 * y2);
+        return (ret1 > 0 && ret2 < 0) || (ret1 < 0 && ret2 > 0);
+    };
+
+    // If lines are intersecting with each other, the relative location should be:
+    // a and b lie in different sides of segment c->d
+    // c and d lie in different sides of segment a->b
+    return twoSided(a, b, c, d) && twoSided(c, d, a, b);
+}
+
+template <typename T>
+bool GeometryUtil<T>::lineIntersectPolygon(const Point<T>& p1, const Point<T>& p2, const Polygon<T>& polygon) {
+    for (auto ring : polygon) {
+        auto length = ring.size();
+        // loop through every edge of the ring
+        for (std::size_t i = 0; i < length - 1; ++i) {
+            if (segmentIntersectSegment(p1, p2, ring[i], ring[i + 1])) {
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
+// ray casting algorithm for detecting if point is in polygon
+template <typename T>
+bool GeometryUtil<T>::pointWithinPolygon(const Point<T>& point, const Polygon<T>& polygon, bool trueOnBoundary) {
+    bool within = false;
+    for (const auto& ring : polygon) {
+        const auto length = ring.size();
+        // loop through every edge of the ring
+        for (std::size_t i = 0; i < length - 1; ++i) {
+            if (pointOnBoundary(point, ring[i], ring[i + 1])) return trueOnBoundary;
+            if (rayIntersect(point, ring[i], ring[i + 1])) {
+                within = !within;
+            }
+        }
+    }
+    return within;
+}
+
+template <typename T>
+bool GeometryUtil<T>::pointWithinPolygons(const Point<T>& point, const MultiPolygon<T>& polygons, bool trueOnBoundary) {
+    for (const auto& polygon : polygons) {
+        if (pointWithinPolygon(point, polygon, trueOnBoundary)) return true;
+    }
+    return false;
+}
+
+template <typename T>
+bool GeometryUtil<T>::lineStringWithinPolygon(const LineString<T>& line, const Polygon<T>& polygon) {
+    const auto length = line.size();
+    // First, check if geometry points of line segments are all inside polygon
+    for (std::size_t i = 0; i < length; ++i) {
+        if (!pointWithinPolygon(line[i], polygon)) {
+            return false;
+        }
+    }
+
+    // Second, check if there is line segment intersecting polygon edge
+    for (std::size_t i = 0; i < length - 1; ++i) {
+        if (lineIntersectPolygon(line[i], line[i + 1], polygon)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+template <typename T>
+bool GeometryUtil<T>::lineStringWithinPolygons(const LineString<T>& line, const MultiPolygon<T>& polygons) {
+    for (const auto& polygon : polygons) {
+        if (lineStringWithinPolygon(line, polygon)) return true;
+    }
+    return false;
+}
+
+template struct GeometryUtil<double>;
+template struct GeometryUtil<int64_t>;
+
+} // namespace mbgl