Option<Vec2> Intersection::get(const Ray& a, const LineSegment& b) {
auto bdir = b.pointB() - b.pointA();
auto blen = bdir.length();
bdir /= blen;
const auto dt = a.m_direction.x * bdir.y - bdir.x * a.m_direction.y;
if (aeq(dt, 0.0f))
return nullptr;
const auto dx = a.m_point.x - b.pointA().x;
const auto dy = a.m_point.y - b.pointA().y;
auto u = (a.m_direction.x * dy - a.m_direction.y * dx) / dt;
auto t = (bdir.x * dy - bdir.y * dx) / dt;
auto pt = a.sampleAlongRay(t);
if (aeq(pt, a.m_point)) {
pt = a.m_point;
t = 0;
}
if (aeq(pt, b.pointA())) {
pt = b.pointA();
u = 0;
}
if (aeq(pt, b.pointB())) {
pt = b.pointB();
u = blen;
}
assert(aeq(pt, b.pointA() + bdir * u));
return t < 0 || u < 0 || u > blen ? nullptr : (Option<Vec2>)pt;
}
Option<Vec2> Intersection::get(const LineSegment& a, const LineSegment& b) {
auto Intersection = get(a.containingLine(), b.containingLine());
if (!Intersection)
return nullptr;
if (aeq(Intersection.value(), a.pointA()))
Intersection = a.pointA();
if (aeq(Intersection.value(), a.pointB()))
Intersection = a.pointB();
if (aeq(Intersection.value(), b.pointA()))
Intersection = b.pointA();
if (aeq(Intersection.value(), b.pointB()))
Intersection = b.pointB();
auto dirA = a.pointB() - a.pointA();
const auto dirALen = dirA.length();
dirA /= dirALen;
auto dirB = b.pointB() - b.pointA();
const auto dirBLen = dirB.length();
dirB /= dirBLen;
const auto t = dot(Intersection.value() - a.pointA(), dirA);
const auto u = dot(Intersection.value() - b.pointA(), dirB);
if (t >= 0 && u >= 0 && t <= dirALen && u <= dirBLen)
return Intersection;
else
return nullptr;
}