Return the distance from the origin of this to the intersection with
other if this intersects with other, or null if the don't intersect.
Source
double intersectsWithSphere(Sphere other) {
final r = other._radius;
final r2 = r * r;
final l = other._center.clone()..sub(_origin);
final s = l.dot(_direction);
final l2 = l.dot(l);
if (s < 0 && l2 > r2) {
return null;
}
final m2 = l2 - s * s;
if (m2 > r2) {
return null;
}
final q = Math.sqrt(r2 - m2);
return (l2 > r2) ? s - q : s + q;
}