intersectsWithSphere method

double intersectsWithSphere (Sphere other)

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.

Implementation 

double intersectsWithSphere(Sphere other) {
  final double r = other._radius;
  final double r2 = r * r;
  final Vector3 l = other._center.clone()..sub(_origin);
  final double s = l.dot(_direction);
  final double l2 = l.dot(l);
  if (s < 0 && l2 > r2) {
    return null;
  }
  final double m2 = l2 - s * s;
  if (m2 > r2) {
    return null;
  }
  final double q = math.sqrt(r2 - m2);

  return (l2 > r2) ? s - q : s + q;
}