I have a question about what the stream might look like from client to server and back. I would like to make use of SDL NET, so it basically takes care of most of the low level stuff.

I looked at this example at gpwiki.org

Here is the loop

while (!quit)
	{
		/* Wait a packet. UDP_Recv returns != 0 if a packet is coming */
		if (SDLNet_UDP_Recv(sd, p))
		{
			printf("UDP Packet incoming\n");
			printf("\tChan:    %d\n", p->channel);
			printf("\tData:    %s\n", (char *)p->data);
			printf("\tLen:     %d\n", p->len);
			printf("\tMaxlen:  %d\n", p->maxlen);
			printf("\tStatus:  %d\n", p->status);
			printf("\tAddress: %x %x\n", p->address.host, p->address.port);
 
			/* Quit if packet contains "quit" */
			if (strcmp((char *)p->data, "quit") == 0)
				quit = 1;
		}		
	}

In this example, the server just prints the incoming packet. My first question is this. Do I understand it correctly, that if a packet contains

->quit, then it simply quits? What I mean is, is it simply a message "quit"?

To better ask my question, maybe someone can clarify this.

If I use the above code, but instead of printing it to the screen I make use of the packets, then what would be a message to move a 2D Tile, up, down, left or right.

In other words, I would like to setup a server and client in SDL. They both load a 10x10 tile map. the server would put a monster in tile (0,0)

and the client would put a player in tile (9,9). So if the server moves the monster right in real time, and the player moves up in real time, what would the back and forth messages look like?

I apoligize, but I might not have the concept down correctly yet. If anyone has a simplified explanation, tutorial, or source example in C++, I would really appreciate it if you can share it?

The goal is a tile based multiplayer game. Perhaps 5 - 10 players, with a larger tile map of course.

Ok, makes sense, but just to make sure we are on the same page. I can come up with my own table of bytes such as ->

mov_u

mov_d

mov_l

mov_r

which corresponds to move up, down, left and right. and I basically pass the message such as mov_l around the internal functions of the client and server right? and I parse it?

Are there any good examples out there for how this can be efficient with both client to server and server to client use? For example, the client will have graphics functions to display the scene, but the server will also (except it would be administrative - so all players can be seen and queried).

Also, to go one step further with the byte example above, am I going the right direction if I create a packet like protocol, so messages are smaller? In other words would I want to do that for efficiency (common sense? or no?)

So there might be an action packet like _ac:m:udlrlrudl and that would mean -> action move up down left right left ... etc. and I implement the parser to handle it locally?

lol - which comes to my next question. After this I can start trying to implement it. How can I keep the server in sync with all clients when moving a monster.

Ok, makes sense, but just to make sure we are on the same page. I can come up with my own table of bytes such as ->

mov_u

mov_d

mov_l

mov_r

which corresponds to move up, down, left and right. and I basically pass the message such as mov_l around the internal functions of the client and server right? and I parse it?

I would probably refrain from passing text.

Its a novice mistake to see the function declaration for send() and see char *buffer and assume that you must pass in a string.

You could just pass opcodes and have a switch statement which will execute faster.

Your network message would be like

unsigned short opcode (uint16_t) (there could be an opcode for moving, or other actions etc)

signed int x, y, z (or float) relative movement

You allocate a buffer, copy the bytes into it. Then send() will take the pointer to the buffer and its size.

When you recv you check the opcode. If its the move position opcode, then you read the rest of the buffer as you wrote to it.