static std::array<int, 3> cross(const std::array<int, 3> &a,
	const std::array<int, 3> &b)
{
	std::array<int, 3> result;
	result[0] = a[1] * b[2] - a[2] * b[1];
	result[1] = a[2] * b[0] - a[0] * b[2];
	result[2] = a[0] * b[1] - a[1] * b[0];
	return result;
}

static bool get_intersection(const cv::Vec4i &line_a,
	const cv::Vec4i &line_b, cv::Point &intersection)
{
	std::array<int, 3> pa{ { line_a[0], line_a[1], 1 } };
	std::array<int, 3> pb{ { line_a[2], line_a[3], 1 } };
	std::array<int, 3> la = cross(pa, pb);
	pa[0] = line_b[0], pa[1] = line_b[1], pa[2] = 1;
	pb[0] = line_b[2], pb[1] = line_b[3], pb[2] = 1;
	std::array<int, 3> lb = cross(pa, pb);
	std::array<int, 3> inter = cross(la, lb);
	if (inter[2] == 0) return false; // two lines are parallel
	else {
		intersection.x = inter[0] / inter[2];
		intersection.y = inter[1] / inter[2];
		return true;
	}
}