How to know if an hotspot is inside the viewport?

I have an hotspot with the attached image changing at intervals as a slide presentation.

I would like to stop the image changing loop when the hotspot exit from the viewport and restart the loop when the hotspot return in the viewport.

To do this I need to know when the hotspot ath/atv are inside the current viewport.

Any suggestion how to get this visibility flag?

Thanks
Marco

Thanks, perfect solution!
Marco