lineIntersection

75mm If a unique intersection point of the lines going through s1,e1 and s2,e2 exists \1, point\ is returned. If no intersection point exists \0, (0,0)\ is returned and if infinitely many exists \-1, (0,0)\ is returned. The wrong position will be returned if P is Point<ll> and the intersection point does not have integer coordinates. Products of three coordinates are used in intermediate steps so watch out for overflow if using int or ll. 15mm

8 lines stress-tested, and tested through half-plane tests

Usage: auto res = lineInter(s1,e1,s2,e2); if (res.first == 1) cout << "intersection point at " << res.second << endl;

Needs: "Point.h"

content/geometry/lineIntersection.h — Victor Lecomte, chilli, source: https://vlecomte.github.io/cp-geo.pdf

template<class P>
pair<int, P> lineInter(P s1, P e1, P s2, P e2) {
	auto d = (e1 - s1).cross(e2 - s2);
	if (d == 0) // if parallel
		return {-(s1.cross(e1, s2) == 0), P(0, 0)};
	auto p = s2.cross(e1, e2), q = s2.cross(e2, s1);
	return {1, (s1 * p + e1 * q) / d};
}