Tutorial 5: Sending Messages to Other Peers

Once you have connected to a session, you can begin game play by sending messages to the other peers in the session for whom you have received a DPN_MSGID_CREATE_PLAYER message. This tutorial extends Tutorial 4 and discusses how to send messages. The complete sample code for this tutorial is included with the Microsoft?DirectX® software development kit (SDK) and can be found at (SDK root)\Samples\C++\DirectPlay\Tutorials\Tut05_Send.

• User's Guide
• Sending a Message
• Receiving a Message
• Terminating the Application

Refer to the preceding tutorials for a discussion of the initial steps in the process:

• Tutorial 1: Creating a DirectPlay Object and Enumerating Service Providers
• Tutorial 2: Hosting a Session
• Tutorial 3: Enumerating Hosted Sessions
• Tutorial 4: Connecting to a Session

User's Guide

When you run this tutorial sample, a window opens and you have the choice to either Host or Connect.

If you choose Host:

1. A window will open and you should enter a session name, then click OK. Your session status will change to 'Hosting Session "YourSessionName".'
2. You can now choose to send a message or disconnect. If you choose to send a message, enter a text string and click Send. If you choose to disconnect, click Disconnect and the session ends.
3. Click Exit to end the sample

If you choose Connect:

1. The Connect to Session window will open and you should enter an Internet Protocol (IP) address and click Search. If any sessions are found at that address, they will be listed in the Detected Sessions box. Select a session and click Connect. If the address does not exist, a message box opens with an error message.
2. Once connected, your session status will change to 'Connected to Session "YourSessionName".' You can now choose to send a message or disconnect. If you choose to send a message, enter a text string and click Send. If you choose to disconnect, click Disconnect.
3. Click Exit to end the sample.

You can run this sample twice—once to host a session and once to connect. When connecting, enter your computer's IP address. Once connected, you can send messages between the host and the client application.

Sending a Message

Once the session is initiated, the peers manage the progress of the game by sending a stream of messages to each other. The content of the message is up to the application but typically includes such information as game state updates or player-to-player communication. Sending a message is straightforward. Select the player you want to send the message to, package your data in a buffer, and pass the data to the target player by calling IDirectPlay8Peer::SendTo. You also have the option of using a single IDirectPlay8Peer::SendTo call to broadcast a message to all players.

The following excerpt from the tutorial sample illustrates how to send a message to every player in the session.

    DPN_BUFFER_DESC dpnBuffer;
    WCHAR           wszData[256];

    dpnBuffer.pBufferData = (BYTE*) wszData;
    dpnBuffer.dwBufferSize = 2 * (wcslen(wszData) + 1);

    hr = g_pDP->SendTo( DPNID_ALL_PLAYERS_GROUP, // dpnid
                                    &dpnBuffer,  // pBufferDesc
                                    1,           // cBufferDesc
                                    0,           // dwTimeOut
                                    NULL,        // pvAsyncContext
                                    NULL,        // pvAsyncHandle
                                    DPNSEND_SYNC |
                                    DPNSEND_NOLOOPBACK );    // dwFlags
									

Receiving a Message

When another player sends you a message, your Microsoft DirectPlay?message handler receives a DPN_MSGID_RECEIVE message containing the data buffer.

The following excerpt from the tutorial sample illustrates a simple message handler for received messages.

//In the receiving player's message handler:

HRESULT WINAPI DirectPlayMessageHandler(void *pvUserContext, DWORD dwMessageId, void *pMsgBuffer)
{
switch( dwMessageId )
{
case DPN_MSGID_RECEIVE:
{
	 case DPN_MSGID_RECEIVE:
        {
            PDPNMSG_RECEIVE     pMsg;

            pMsg = (PDPNMSG_RECEIVE) pMsgBuffer;
			//process message
			 .
			 .
			 .
            break;
        }

}
}
return(DPN_OK);
}

Terminating the Application

If a DirectPlay peer object was successfully initialized, you should first close the object by calling IDirectPlay8Peer::Close; then release all active objects and terminate the application. See Tutorial 1 for further discussion.