4. Tracking Players Using Maps

You're going to use a map to track the number of eliminations a player has scored. Maps provide a handy association of keys to values, and in this tutorial, you’ll use the player as the key and their associated weapon tier (represented as an int) as the value. That way, you can retrieve a player’s current tier given just a reference to the player. An example of how a map of player-to-weapon tier associations might look is provided below.

Follow these steps to set up and populate your map of players:

1. Add [player]int map named PlayerMap to the team_elimination_game class. This stores a reference to each player and their weapon tier.

   Verse

        team_elimination_game := class(creative_device):
            var PlayerMap : [player]int = map{}
   

   Copy full snippet(2 lines long)

2. Add a new method PopulateTeamsAndPlayers() to the team_elimination_game class. This method populates your PlayerMap, and will be called from OnBegin().

   Verse

        PopulateTeamsAndPlayers() : void=
        Print("Beginning to populate players")
   

   Copy full snippet(2 lines long)

3. Add a new method, OnPlayerEliminated, to the team_elimination_game class. This is called whenever a player is eliminated, and will determine who the eliminating player is by accessing the elimination_result struct passed as an argument.

   Verse

        OnPlayerEliminated(Result : elimination_result) : void=
            Print("A Player was eliminated!")
   

   Copy full snippet(2 lines long)

4. When the game begins, you need to iterate through the list of players and set them all to the first weapon tier. Inside PopulateTeamsAndPlayers, get all players using GetPlaySpace().GetPlayers() and save them in an array AllPlayers. For each player, retrieve the FortCharacter for that player and save it in a variable FortCharacter. Set that player’s score in the PlayerMap to 0 to represent the first weapon in the WeaponGranters array, then subscribe FortCharacter.EliminatedEvent() to OnPlayerEliminated.

   Verse

        AllPlayers := GetPlayspace().GetPlayers()
        for (Agent : AllPlayers, TeamPlayer := player[Agent], FortCharacter := TeamPlayer.GetFortCharacter[]):
            if(set PlayerMap[TeamPlayer] = 0, WeaponTier := PlayerMap[TeamPlayer]):
                Print("Assigned Player to PlayerMap with Tier {WeaponTier}")
                FortCharacter.EliminatedEvent().Subscribe(OnPlayerEliminated)
   

   Copy full snippet(5 lines long)

5. With a reference to the player’s score in the PlayerMap set, you can grant players their first weapon. Modify OnPlayerSpawn to grant players their first weapon. When a player spawns, retrieve their weapon tier from PlayerMap and store it in a variable WeaponTier, then call GrantWeapon passing WeaponTier and a reference to the player.

   Verse

        OnPlayerSpawn(InPlayer : agent) : void =
            Print("A player just spawned!")
                if(WeaponTier := PlayerMap[InPlayer]):
                    GrantWeapon(option{InPlayer}, WeaponTier)
                    Print("Spawned Player was granted a gun of tier {WeaponTier}")
   

   Copy full snippet(5 lines long)

6. Save the script in Visual Studio Code, compile it, and click Launch Session in the UEFN toolbar to playtest the level. When you playtest your level, you should spawn with the first weapon in the WeaponGranters array. Verify this behavior with the log.

Mapping Teams of Players

With your map of players set up, it’s helpful to think about how you check a player’s score. Since your script will automatically promote the player on the team with the least eliminations, it is not useful to check the weapon tier of the enemy team’s players. You might already see a problem emerging, since PlayerMap doesn’t differentiate between teams.

To get around this problem, you can use another map. For this, you’ll adapt the PlayerMap you set up previously into a nested map system. Since key-value pairs in a map can be any pairs of types, it makes sense that a team key could have another map as its value. The first map will associate teams (key) to another map of players on that team (value). The inner map will associate players (key) to their score (value).

Now, given a player, you can verify what team they’re on using GetTeam(). From there you can retrieve a list of teammates to compare the number of eliminations against.

The syntax of the nested map [team][player]int might not be clear. To make this easier to understand, you can take advantage of type aliasing to create a simpler name to reference the map. In this tutorial you’ll give [player]int the alias of player_map. This means you can use the name player_map any time you would need [player]int, and the nested map can be rewritten as [team]player_map, or a map that associates teams to maps of players.

Follow these steps to adapt your map into a nested map system:

1. Above the team_elimination_game class definition, add an alias for [player]int named player_map.

   Verse

        player_map := [player]int # This is a type alias!
        team_elimination_game := class(creative_device):
   

   Copy full snippet(2 lines long)

2. Replace the PlayerMap variable you set up earlier in team_elimination_game with a new variable TeamMap of type [team]player_map.

   Verse

        # Map of Team Maps, where the key is the team and the value is a map of
        # player->int key-value pairs
        var TeamMap : [team]player_map = map{}
   

   Copy full snippet(3 lines long)

3. Since the value of TeamMap is of type player_map, for each team, you need to initialize a map of players, populate them, set each player’s score to 0, then assign the map of players to TeamMap. Modify PopulateTeamsAndPlayers() with the updated code.

   • For each team, retrieve the players in that team and store them in a variable TeamPlayers. Initialize a new variable PlayerMap of type player_map to map players to their score.

     Verse

       PopulateTeamsAndPlayers() : void=
           Print("Beginning to populate players")
           for (Team : Teams, TeamPlayers := GetPlayspace().GetTeamCollection().GetAgents[Team]):
               var PlayerMap : player_map = map {}
     

     Copy full snippet(4 lines long)

   • For each player in TeamPlayers, retrieve the FortCharacter for that player and save it in a variable FortCharacter. Set that player’s score in the PlayerMap to 0 to represent the first weapon in the WeaponGranters array, then subscribe FortCharacter.EliminatedEvent() to OnPlayerEliminated.

     Verse

       PopulateTeamsAndPlayers() : void =
           Print("Beginning to populate players")
           for (Team : Teams, TeamPlayers := GetPlayspace().GetTeamCollection().GetAgents[Team]):
               var PlayerMap : player_map = map {}
               for (Agent : TeamPlayers, TeamPlayer := player[Agent], FortCharacter := Agent.GetFortCharacter[]): 
                   if(set PlayerMap[TeamPlayer] = 0, WeaponTier := PlayerMap[TeamPlayer]): 
                       Print("Assigned Player to PlayerMap with Tier {WeaponTier}")
                   FortCharacter.EliminatedEvent().Subscribe(OnPlayerEliminated) 
     

     Copy full snippet(8 lines long)

   • Finally, set PlayerMap as the value of the current Team key in TeamMap. Your PopulateTeamsAndPlayers code should look like below.

     Verse

       PopulateTeamsAndPlayers() : void =
           Print("Beginning to populate players")
           for (Team : Teams, TeamPlayers := GetPlayspace().GetTeamCollection().GetAgents[Team]):
               var PlayerMap : player_map = map {}
               for (Agent : TeamPlayers, TeamPlayer := player[Agent], FortCharacter := Agent.GetFortCharacter[]): 
                   if(set PlayerMap[TeamPlayer] = 0, WeaponTier := PlayerMap[TeamPlayer]): 
                       Print("Assigned Player to PlayerMap with Tier {WeaponTier}")
                   FortCharacter.EliminatedEvent().Subscribe(OnPlayerEliminated) 
               if(set TeamMap[Team] = PlayerMap):
                   Print("Successfully set this team in the TeamMap")
     

     Copy full snippet(10 lines long)

4. Once you've set the TeamMap, update OnPlayerSpawn to access a player’s team using GetTeam[] and store it in a local variable PlayerTeam. Set WeaponTier by retrieving the player’s current score from TeamMap, using both PlayerTeam and a reference to the player. The updated OnPlayerSpawn() should look like the following code.

   Verse

        OnPlayerSpawn(InPlayer : agent) : void =
             Print("A player just spawned!")
            if:
                PlayerTeam := GetPlayspace().GetTeamCollection().GetTeam[InPlayer]
                WeaponTier:int := TeamMap[PlayerTeam][InPlayer]
            then:
                GrantWeapon(option{InPlayer}, WeaponTier)
                Print("Spawned Player was granted a gun of tier {WeaponTier}")
   

   Copy full snippet(8 lines long)

Save the script in Visual Studio Code, compile it, and click Launch Session in the UEFN toolbar to playtest the level. When you playtest your level, you should again spawn with the first weapon in the WeaponGranters array. Verify this behavior with the log.

Next Step

In the next step of this tutorial, you’ll learn how to grant players weapons when they score an elimination.