One of Unity's most excited new features, for me at least, was the new built-in Netcode for Gameobjects library and functionality introduced in version 2021.3, however now fully released in the 2023 LTS! It allows us to build networking logic into our games quite easily through their Unity Cloud Service and the use of Server/Client RPC requests.
An RPC is short for 'Remote Prodecure Call' and essentially can be called by Clients to trigger on the server or by the server/host to be triggered on the clients
One example of when we want to call an RPC as a client to the server is to let the host know we've changed our weapon, then it's the responsibility of the server to let everyone else know that you're carrying a new weapon.
You may be wondering why the client can't just let all the other clients know without first alerting the host. Well this is a safety precaution that allows the server to check that the call being made was 'legal' and not a nasty cheater trying to hack the game in his favor.
Client A: Tells the Server he shot Client B for 100 damage
Host: Accepts parameters given by Client A and then share that information with all other clients
Client A: Tells the Server he shot client B with a cheap pistol
Host: Checks Client A's weapon, generates the damage amount that would normally be given by that weapon, applies it to Client B and shares that info
One problem with the good example is that as Client A, we wouldn't want to have to wait until the Host has ran through all of it's logic and sent us back the amount of damage we've done. Therefore to get around this, we make it seem like we've damaged Client through feedback and animation, then adjust the health when it has been returned.
Unity Services also has a library for lobbies which makes this part really easy, creating one looks a little like this:
CreateLobbyOptions lobbyOptions = new CreateLobbyOptions
{
IsPrivate = false,
Player = GetPlayer(),
Data = new Dictionary
{
{
KEY_START_GAME,
new DataObject(DataObject.VisibilityOptions.Member, "0")
}
}
};
Lobby lobby = await LobbyService.Instance.CreateLobbyAsync(lobbyName, maxPlayers, lobbyOptions);
You'll need to build a UI for this ofcourse. But once a lobby is created, we can use the below to get all public lobbies and display them on a board
QueryResponse queryResponse = await Lobbies.Instance.QueryLobbiesAsync();
If you decide to create private lobbies, a lobby code is generated when created. You can share this with people you want to play with and the logic
for them to join will look like this:
var joinLobbyByCodeOptions = new JoinLobbyByCodeOptions() { Player = GetPlayer() };
var joinedLobby = await Lobbies.Instance.JoinLobbyByCodeAsync(lobbyCode, joinLobbyByCodeOptions);
In the following example I'm about to give, when a player joins my server, I need everyone to see the moving obstacles at in the exact same position at the exact same time. If this is done incorrectly, some players may appear to be floating or possibly cheating.
[ClientRpc]
void SetObstaclePositionClientRpc(ulong clientId, float timeElapsed, bool isReversing)
{
var obstacle = GetNetworkObject(clientId).GetComponent();
obstacle.TimeElapsed = timeElapsed;
if (obstacle.HasReverse)
{
obstacle.GetComponent().Reverse = isReversing;
}
}
If you remember earlier I mentioned that the Server has to call an RPC that will trigger on the clients. This means each client will be told to run this method that says the objects ID (ulong), the time already elapsed during it's cycle (float) and wether or not it's going it's original way or reversing (bool).
This should only need to be called once when the player first enters, afterwards the cycle should be completely predictable and never go off course. Bare in mind that you wouldn't use this logic for something like a football since you need to know at all times where it's exact position is during the game.
A very light introduction to Unity Networking, but for me these bits of information really helped string together a bigger picture of just how much thought and effort goes into making online multiplayer games seamless and enjoyable to play with friends. Thanks for taking the time to read this blog and don't forget to check out my others!