Repo created

libs/geometry/segment2d.cpp

@@ -0,0 +1,100 @@
+#include "geometry/segment2d.hpp"
+
+#include "geometry/line2d.hpp"
+#include "geometry/robust_orientation.hpp"
+
+#include <algorithm>
+#include <sstream>
+#include <string>
+
+namespace m2
+{
+bool IsPointOnSegmentEps(PointD const & pt, PointD const & p1, PointD const & p2, double eps)
+{
+  double const t = robust::OrientedS(p1, p2, pt);
+
+  if (std::fabs(t) > eps)
+    return false;
+
+  double minX = p1.x;
+  double maxX = p2.x;
+  if (maxX < minX)
+    std::swap(maxX, minX);
+
+  double minY = p1.y;
+  double maxY = p2.y;
+  if (maxY < minY)
+    std::swap(maxY, minY);
+
+  return pt.x >= minX - eps && pt.x <= maxX + eps && pt.y >= minY - eps && pt.y <= maxY + eps;
+}
+
+bool IsPointOnSegment(PointD const & pt, PointD const & p1, PointD const & p2)
+{
+  // The epsilon here is chosen quite arbitrarily, to pass paranoid
+  // tests and to match our real-data geometry precision. If you have
+  // better ideas how to check whether pt belongs to (p1, p2) segment
+  // more precisely or without kEps, feel free to submit a pull
+  // request.
+  double constexpr kEps = 1e-100;
+  return IsPointOnSegmentEps(pt, p1, p2, kEps);
+}
+
+bool SegmentsIntersect(PointD const & a, PointD const & b, PointD const & c, PointD const & d)
+{
+  using std::max, std::min;
+  return max(a.x, b.x) >= min(c.x, d.x) && min(a.x, b.x) <= max(c.x, d.x) && max(a.y, b.y) >= min(c.y, d.y) &&
+         min(a.y, b.y) <= max(c.y, d.y) && robust::OrientedS(a, b, c) * robust::OrientedS(a, b, d) <= 0.0 &&
+         robust::OrientedS(c, d, a) * robust::OrientedS(c, d, b) <= 0.0;
+}
+
+IntersectionResult Intersect(Segment2D const & seg1, Segment2D const & seg2, double eps)
+{
+  if (!SegmentsIntersect(seg1.m_u, seg1.m_v, seg2.m_u, seg2.m_v))
+    return IntersectionResult(IntersectionResult::Type::Zero);
+
+  Line2D const line1(seg1);
+  Line2D const line2(seg2);
+  auto const lineIntersection = Intersect(line1, line2, eps);
+  if (lineIntersection.m_type != IntersectionResult::Type::One)
+    return lineIntersection;
+
+  if (IsPointOnSegmentEps(lineIntersection.m_point, seg1.m_u, seg1.m_v, eps) &&
+      IsPointOnSegmentEps(lineIntersection.m_point, seg2.m_u, seg2.m_v, eps))
+  {
+    return lineIntersection;
+  }
+
+  return IntersectionResult(IntersectionResult::Type::Zero);
+}
+
+std::string DebugPrint(Segment2D const & segment)
+{
+  return "(" + DebugPrint(segment.m_u) + ", " + DebugPrint(segment.m_v) + ")";
+}
+
+std::string DebugPrint(IntersectionResult::Type type)
+{
+  using Type = IntersectionResult::Type;
+
+  switch (type)
+  {
+  case Type::Zero: return "Zero";
+  case Type::One: return "One";
+  case Type::Infinity: return "Infinity";
+  }
+  UNREACHABLE();
+}
+
+std::string DebugPrint(IntersectionResult const & result)
+{
+  std::ostringstream os;
+  os << "Result [";
+  if (result.m_type == IntersectionResult::Type::One)
+    os << DebugPrint(result.m_point);
+  else
+    os << DebugPrint(result.m_type);
+  os << "]";
+  return os.str();
+}
+}  // namespace m2