Joining a game

Connect to a hosted game as a client

To join a multiplayer game, a player must connect to an existing server using the SetupClient() function. This establishes a connection to the host and allows both players to begin the match.

How joining works

1. Create the client host

   First, create a client-side ENet host:

   main.cpp

   clientHost = enet_host_create(
       NULL,  // create a client host
       1,     // only 1 outgoing connection
       2,     // allow up to 2 channels
       0,     // unlimited download bandwidth
       0      // unlimited upload bandwidth
   );
   

   Passing NULL as the first parameter creates a client host that can initiate connections but not accept them.

2. Verify client creation

   Check if the client host was created successfully:

   main.cpp

   if (clientHost == NULL){
       printf("failed to create client host\n");
       return false;
   }
   

   If creation fails, the game returns to the main menu.

3. Configure server address

   Set up the address of the server to connect to:

   main.cpp

   ENetAddress address;
   enet_address_set_host(&address, SERVER_IP);
   address.port = SERVER_PORT;
   

   The enet_address_set_host() function resolves the hostname or IP address (by default “127.0.0.1”) to an ENet address.

4. Connect to the server

   Initiate the connection to the server:

   main.cpp

   serverPeer = enet_host_connect(clientHost,
       &address,  
       2,  // number of channels
       0   // user data
   );
   if (serverPeer == NULL){
       printf("failed to connect to server");
       return false;
   }
   printf("Connecting to %s:%d...\n",SERVER_IP,SERVER_PORT);
   return true;
   

   This returns a peer object representing the connection to the server.

5. Wait for connection confirmation

   The game enters the JOINING state and waits for the connection to be established:

   main.cpp

   ENetEvent event;
   while (enet_host_service(clientHost, &event, 0) > 0) {
       if (event.type == ENET_EVENT_TYPE_CONNECT) {
           printf("Connected to server!\n");
           connectionState = "CONNECTED";
           
           // Start the game
           state = "MULTIPLAYER";
       }
   }
   

   Once the connection is confirmed, the game transitions to the multiplayer gameplay state.

Complete SetupClient function

main.cpp

bool SetupClient() {
    // create a client host
    clientHost = enet_host_create(
        NULL,
        1,
        2,
        0,
        0
    );
    if (clientHost == NULL){
        printf("failed to create client host\n");
        return false;
    }

    ENetAddress address;
    enet_address_set_host(&address, SERVER_IP);
    address.port = SERVER_PORT;

    serverPeer = enet_host_connect(clientHost,
        &address,  
        2,
        0
    );
    if (serverPeer == NULL){
        printf("failed to connect to server");
        return false;
    }
    printf("Connecting to %s:%d...\n",SERVER_IP,SERVER_PORT);
    return true;
}

Network variables

The following global variables manage the client connection:

main.cpp

ENetHost* clientHost = nullptr;
ENetPeer* serverPeer = nullptr; // for client connection to server

When joining, the client uses clientHost to manage its networking and stores the server connection in serverPeer.

Connection to localhost vs LAN

By default, the game connects to 127.0.0.1 (localhost), which only works if both players are on the same machine.

For LAN play, modify the SERVER_IP constant to the host’s local network IP address:

main.cpp

const char* SERVER_IP = "192.168.1.100"; // Replace with host's IP

Ensure both players are on the same network and the host’s firewall allows incoming connections on port 7777.

Troubleshooting

If connection fails:

• Verify the server is running and in the HOSTING state
• Check that SERVER_IP points to the correct host address
• Ensure port 7777 is not blocked by firewall rules
• Confirm ENet has been initialized before calling SetupClient()