Optional

gistfile1.cpp

#include <optional>
#include <iostream>

struct Point {
    Point(float x, float y): x{x}, y{y} {
    }
    
    float x;
    float y;
};
using Line = std::pair<Point, Point>;

Point operator+(const Point& p0, const Point& p1) {
    return Point{p0.x + p1.x, p0.y + p1.y};
}

Point operator-(const Point& p0, const Point& p1) {
    return Point{p0.x - p1.x, p0.y - p1.y};
}

Point operator*(float s, const Point& p) {
    return Point{s * p.x, s * p.y};
}


std::optional<Point> intersection(const Line& a, const Line& b) {
    const auto d1 = a.first - a.second;
    const auto d2 = b.first - b.second;

    const auto cross = d1.x * d2.y - d1.y * d2.x;
    if (std::abs(cross) < 1e-6f) { // No intersection
        return {};
    }
    
    const auto x = b.first - a.first;
    const auto t1 = (x.x * d2.y - x.y * d2.x) / cross;
    return a.first + t1 * d1;
}

int main() {
    
    const auto i0 = intersection(Line(Point(-1, 0), Point(1, 0)), Line(Point(0, -1), Point(0, 1)));
    std::cout << std::boolalpha << i0.has_value();
    if(i0) {
        std::cout << " : " << i0->x << ", " << i0->y;
    }
    std::cout << '\n';
    
    const auto i1 = intersection(Line(Point(-1, 0), Point(1, 0)), Line(Point(-1, 5), Point(1, 5)));
    std::cout << std::boolalpha << i1.has_value();
    if(i1) {
        std::cout << " : " << i1->x << ", " << i1->y;
    }
    std::cout << '\n';
    
    return 0;
}