How does a bot know who is an enemy?

Question

How does a bot know who is an enemy if "enemy" encompasses not only one player, which can be just hardcoded?

For example, in Warcraft 3, we can have two bot teams with faction alliances and they will treat each other as enemies.

What is the mechanism that chooses who is an ally and who is an enemy?

I suppose there is some Map<Team, List< Units >> and every bot is assigned some Team by default at the start, and when bot sees someone and that unit is not in the bot's team it means it is an enemy? But here is no place for allies.

Edit: So I am working on 2d Farm Game and I plan to add another enemy to me fraction and some enemies for all fractions.
Currently I don't have any NPC but later I want to have some units that can gather resources/kill enemies. So I was thinking that there is no difference between my units and enemy units.So there should be some rules that define that this bot treats another bot as ally or an enemy.

PS: The reason I started thinking about that was that I started working on inventory and understood that ideally there should be no difference between me and an npc who gathered a particular resource, so there should be some way to add a resource to same inventory by player controlled character and a bot. This led me thinking that the same should be true for another team, the code should be the same. There shouldn't be FriendlyBot and EnemyBot.Just Bot script for example and some script that assigns team id and later using this team id bot will interact with an inventory.

It seems to me that two topics are pretty close to each other as both need a structure that would allow me to organize bots into teams and inventory belongs to the whole team.

Answer 1

Unity has tags and Godot has Groups.

you can put the player into group/tag "player" and the enemy AI will know who is the player.

or use Team1/Team2/Team3

or maybe use "playerID_insert_number_here" for npcs that follow specific players in an online game.

Alternatively you can use GameObject.Find("insert objsect to find") in unity or get.node("insert node to find") in godot but this last method usually doesn't work for multiplayer games

in other game engines or if you are not using a game engine, you could probably just use variables inside the player script like creating an area around the enemy with code and basically saying

if anything touches the area: 
  proceed: 
  if anything in the area has method/variable "player" 
     proceed: 
else : 
    enemy AI does whatever it should do when no players are around 

and you can make as many if/else statements as needed for all the states the AI has, maybe put them into functions() and call each function when needed or use switch case but I've never used switch case so i don't know. But people more expert than me say the less nested if-else statements you use, the better.

Anyway you always rather use tags and groups since it easily works in multiplayer and it's the most performing one becase no area is created around the enemy.

one area can be unnoticeable, but get 20 enemies and that's 20 areas around them... each one needs to get update every single frame.

I personally found incredible performance boosts by not using areas.

Answer 2

In addition to what Cei mentioned, you can accomplish this in Unity by creating a sphere around the object you wish to detect enemies or players as i demonstrate below ,however this system has the disadvantage that enemies may be able to detect you without seeing you. If you were to make the next GTA, it would be unreal so another approach to this issue is make the enemy cast a ray while patrolling around the map

private void Detect()
{

    Collider[] detectedColliders = Physics.OverlapSphere(transform.position, raduis){


        for (int i = 0; i < detectedColliders.Length; i++)
        {

            if (detectedColliders[i].CompareTag("Player")){



                if (!HasTarget)
                {
                    // Do what ever you want the enemy/npc to do 

                    HasTarget = true;
                }

            }
            else
            {
                // Idle 
            }

        }

    }

}