Server and Client Communications (Sort Of)

In a typical gaming environment there is a "game server" which is responsible for tracking all the communications between players (clients) within the game. Communications can be considered anything from the chat function, to the location of bullets within the game. Pretty much any piece of data that one player needs to send to another goes through the game server.

(That was in its simplest form, it is more complicated than that...go google it)

With a PBBG it gets a little tricky because there is no game server in play, its all cron jobs and reactions to players. (This is due to web development being "stateless"....again go google it, its why web programming is "different")

I use the following code to send interactions between two or more players. Pretty much you have a table that translates the game commands to each player...however the client code (javascript) has to be a bit smarter to handle the "statelessness" of the content)

See it in Action (note, you will have to enable popups)

If you want to implement it, you will need to create the following two tables.

User Table: Hopefully you allready have one of these, if so just add lastCommID to it.

CREATE TABLE `lab_user` (
`userID` INT NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`userName` VARCHAR( 20 ) NOT NULL ,
`lastCommID` INT NOT NULL
) ENGINE = MYISAM ;

Command Table: "Meat of the code"

CREATE TABLE `lab_command` (
`commID` INT NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`userID` INT NOT NULL ,
`command` VARCHAR( 20 ) NOT NULL ,
`commandOptions` VARCHAR( 255 ) NOT NULL
) ENGINE = MYISAM ;

You can download the source here.

Please keep in mind...USER IDs are HARD CODED in the source...you will need to config/play with that yourself.


For those that just like to "look". Here is some javascript....

var xmlHttpDivID = "";
var ajaxInUse = false;
var readyToSend = true;

function getXmlHttpObject(handler)
{
var objXMLHttp=null;
if (window.XMLHttpRequest)
{
objXMLHttp=new XMLHttpRequest()
}
else if (window.ActiveXObject)
{
objXMLHttp=new ActiveXObject("Microsoft.XMLHTTP")
}

if(objXMLHttp == null)
{
alert("Your browser is not AJAX/Web 2.0 enabled");
}

return objXMLHttp;
}

//////////////////////////////////////////////////////////////////////////
//
//
// Sending the commands to the server
//
//
//
//////////////////////////////////////////////////////////////////////////
function mouseClicked(e)
{
if(readyToSend)
{
pos = getMousePos(e);
sendCommand("move", "player_|" + pos[0] + "," + pos[1]);
}
else
{
log("Waiting for a listener!");
}
}

function sendCommand(command, options)
{
if(!ajaxInUse)
{
ajaxInUse = true;

xmlHttp=getXmlHttpObject();
xmlHttp.onreadystatechange=commandSent;

url="commandHandler.php?action=sendComm";
url+="&userID="; //very bad, change this for testing...
url+="&command=" + command;
url+="&options=" + options;
url+="&cache_killer=" + Math.random();
xmlHttp.open("GET",url,true)
xmlHttp.send(null);
log("Command Sent");
}
else
{
log("Ajax is in use...try later");
}
}

function commandSent()
{
if (xmlHttp.readyState==4)
{
log("Command Sent and Done");
ajaxInUse = false;
}
}



//////////////////////////////////////////////////////////////////////////
//
//
// Reading Commands from the server
//
//
//
//////////////////////////////////////////////////////////////////////////
var commTimerID = "";

function startListening()
{
requestNextHttp=getXmlHttpObject();

url="commandHandler.php?action=start";
url+="&userID="; //very bad, change this for testing...
url+="&cache_killer=" + Math.random();
requestNextHttp.open("GET",url,true)
requestNextHttp.send(null);
//log("Ask for next command");
requestNextCommand();

}



function requestNextCommand()
{
requestNextHttp=getXmlHttpObject();
requestNextHttp.onreadystatechange=processCommand;

url="commandHandler.php?action=getComm";
url+="&userID="; //very bad, change this for testing...
url+="&cache_killer=" + Math.random();
requestNextHttp.open("GET",url,true)
requestNextHttp.send(null);
//log("Ask for next command");
clearTimeout(commTimerID);
}

function processCommand()
{
if (requestNextHttp.readyState==4)
{
str = requestNextHttp.responseText;

if(str != "")
{
log2(requestNextHttp.responseText);
performCommand(str);
}

commTimerID = setTimeout("requestNextCommand()", 3000);
}
}

function performCommand(str)
{
data = str.split("|");

if(data.length > 2)
{
commID = data[0];
sentByUserID = data[1];
command = data[2];

if(command == "move")
{
objID = data[3];
pos = data[4].split(",");
destX = pos[0];
destY = pos[1];
log("Moving " + objID + " to " + destX + "," + destY);
setDest(objID, destX, destY);
}
}
}



//
//add the event to the document
//
document.onclick = mouseClicked;
document.onload = startListening();