code: protected boolean intersectsX (IRay3 ray, float x) {
          IVector3 origin = ray.origin(), dir = ray.direction();
          float t = (x - origin.x()) / dir.x();
          if (t < 0f) {
              return false;
          }
          float iy = origin.y() + t*dir.y(), iz = origin.z() + t*dir.z();
          return iy >= _minExtent.y && iy <= _maxExtent.y &&
              iz >= _minExtent.z && iz <= _maxExtent.z;
      }
docs: Helper method for {@link #intersects(Ray3)}. Determines whether the ray intersects the box
  at the plane where x equals the value specified.