AI Perception Behavior Enhancement

In HL2, if an idle NPC hears a sound but doesn't see its emitter, it will only turn in the direction of the sound for a time before returning to its previous action.

With the modification below the NPC will instead investigate the source of the sound.

Open the ai_basenpc_schedule.cpp file and look for the function SelectAlertSchedule(). Look for the following code:

	if ( HasCondition ( COND_HEAR_DANGER ) ||
			  HasCondition ( COND_HEAR_PLAYER ) ||
			  HasCondition ( COND_HEAR_WORLD  ) ||
			  HasCondition ( COND_HEAR_BULLET_IMPACT ) ||
			  HasCondition ( COND_HEAR_COMBAT ) )
	{
		return SCHED_ALERT_FACE_BESTSOUND;

	}

Replace this code with:

	if ( HasCondition ( COND_HEAR_DANGER ) ||
			  HasCondition ( COND_HEAR_PLAYER ) ||
			  HasCondition ( COND_HEAR_WORLD  ) ||
			  HasCondition ( COND_HEAR_BULLET_IMPACT ) ||
			  HasCondition ( COND_HEAR_COMBAT ) )
	{
		
			  return SCHED_INVESTIGATE_SOUND;//E.Y.E , AI Search for the source of alert  sound
	}

Conclusion

With this code,as soon as NPC will hear alert sound, they will investigate. I use this for my own project E.Y.E and it runs perfectly.