If he/they are warned, then warned a second time with hand on gun, and warned a third time with gun drawn and pointed at him/them and they are still coming, he/they intend you harm.
If the person's approach toward me is aggressive and he fails to stop after being commanded to do so, I would then place my hand on my pistol, slightly pulling it from from holster retention. Another forceful command would be issued. If at this point he still shows aggression and has refused to obey, I would be forced to clear leather and show this person I am not kidding. If he then continues to approach with a muzzle pointed at him, I have to assume he intends to harm me in some way.
My shot(s) would be fired to stop his forward advances.