geometry/cross_point_ll.hpp

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• Last update: 2025-08-16 01:23:21+09:00
• Include: #include "geometry/cross_point_ll.hpp"

Depends on

• geometry/base.hpp
• geometry/line.hpp
• geometry/point.hpp

Required by

• geometry/convex_polygon_cut.hpp

Verified with

• test/verify/aoj-cgl-2-c.test.cpp
• test/verify/aoj-cgl-4-c.test.cpp

Code

#include "base.hpp"
#include "line.hpp"

namespace geometry {
Point cross_point_ll(const Line& l, const Line& m) {
  Real A = cross(l.b - l.a, m.b - m.a);
  Real B = cross(l.b - l.a, l.b - m.a);
  if (equals(abs(A), 0) && equals(abs(B), 0)) return m.a;
  return m.a + (m.b - m.a) * B / A;
}
}  // namespace geometry

#line 2 "geometry/base.hpp"

namespace geometry {
using Real = double;
const Real EPS = 1e-8;
const Real PI = acos(static_cast<Real>(-1));

enum { OUT, ON, IN };

inline int sign(const Real& r) { return r <= -EPS ? -1 : r >= EPS ? 1 : 0; }

inline bool equals(const Real& a, const Real& b) { return sign(a - b) == 0; }
}  // namespace geometry
#line 3 "geometry/point.hpp"

namespace geometry {
using Point = complex<Real>;

istream& operator>>(istream& is, Point& p) {
  Real a, b;
  is >> a >> b;
  p = Point(a, b);
  return is;
}

ostream& operator<<(ostream& os, const Point& p) {
  return os << real(p) << " " << imag(p);
}

Point operator*(const Point& p, const Real& d) {
  return Point(real(p) * d, imag(p) * d);
}

// rotate point p counterclockwise by theta rad
Point rotate(Real theta, const Point& p) {
  return Point(cos(theta) * real(p) - sin(theta) * imag(p),
               sin(theta) * real(p) + cos(theta) * imag(p));
}

Real cross(const Point& a, const Point& b) {
  return real(a) * imag(b) - imag(a) * real(b);
}

Real dot(const Point& a, const Point& b) {
  return real(a) * real(b) + imag(a) * imag(b);
}

bool compare_x(const Point& a, const Point& b) {
  return equals(real(a), real(b)) ? imag(a) < imag(b) : real(a) < real(b);
}

bool compare_y(const Point& a, const Point& b) {
  return equals(imag(a), imag(b)) ? real(a) < real(b) : imag(a) < imag(b);
}

using Points = vector<Point>;
}  // namespace geometry
#line 3 "geometry/line.hpp"

namespace geometry {
struct Line {
  Point a, b;

  Line() = default;

  Line(const Point& a, const Point& b) : a(a), b(b) {}

  Line(const Real& A, const Real& B, const Real& C) {  // Ax+By=C
    if (equals(A, 0)) {
      assert(!equals(B, 0));
      a = Point(0, C / B);
      b = Point(1, C / B);
    } else if (equals(B, 0)) {
      a = Point(C / A, 0);
      b = Point(C / A, 1);
    } else if (equals(C, 0)) {
      a = Point(0, C / B);
      b = Point(1, (C - A) / B);
    } else {
      a = Point(0, C / B);
      b = Point(C / A, 0);
    }
  }

  friend ostream& operator<<(ostream& os, Line& l) {
    return os << l.a << " to " << l.b;
  }

  friend istream& operator>>(istream& is, Line& l) { return is >> l.a >> l.b; }
};

using Lines = vector<Line>;
}  // namespace geometry
#line 3 "geometry/cross_point_ll.hpp"

namespace geometry {
Point cross_point_ll(const Line& l, const Line& m) {
  Real A = cross(l.b - l.a, m.b - m.a);
  Real B = cross(l.b - l.a, l.b - m.a);
  if (equals(abs(A), 0) && equals(abs(B), 0)) return m.a;
  return m.a + (m.b - m.a) * B / A;
}
}  // namespace geometry

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