ofCamera nearClip and farClip both setting to zero?

Hi, what happens if nearClip and farClip are set to zero?

When I set both to zero and move object far away from the camera, I could see the object far enough until it disappeared.

But if I set nearClip to 0 and farClip to 1, the object disappeared immediately.

And if I set nearClip to 0 and farClip to -1, the object doesn’t seem to be clipped even when the object gets really far.

Can some one please explain how nearClip and farClip exactly work?