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<html>
<head>
<title>Documentation for libkdegames</title>
<meta content="">
<style></style>
</head>
<body>
<H1>Documentation for the classes in libkdegames</H1>
<!-------------------------------------------------------------------------------->
<H3>Design Principles</H3>
The library <em>kdegames</em> contains a collection of classes that can be used
to develop games using the KDE environment very easily. There are a few
principles that were used when developing the library:<P>
<UL>
<LI><b>usable for a big variety of games</b><br>
The class <em>KGame</em> provides many features that are needed in many games.
It can be used for board games, card games, maze games, simulation games, strategy games and
many more.<br>
It does not (yet) include special features for realtime games, but can be used there, too.
<LI><b>features one-player and multi-player games</b></br>
A game developed with this library can easily support any number of simultaneous players.
So use it for one-player games (like Tetris or KSame), for two-player games (like TicTacToe
or chess) or for games with an arbitrary number of players.
<LI><b>computer players can easily be developed</b><br>
The class <em>KPlayer</em> represents an abstract player in a game. This can be a
human player that gets the input from the mouse or the keyboard. Or it can be a computer
player that makes moves by random or with artificial intelligence. All this can be achieved
subclassing KPlayer.
<LI><b>support for network games transparently</b><br>
The class <em>KGame</em> contains lots of features for network game support. Developing
a network game using a TCP/IP connection is very easy this way. But the default
case is still the local game. So the user should not need to connect to the internet
or to select a game server to play a game.
<LI><b>support for turn based and for asynchronous games</b><br>
You can use this library for turn based games, when only one player can make a move at a time
(like most bord games or card games), but also for asynchronous games, when every player can
make a move any time (like many action games).
</UL>
<!-------------------------------------------------------------------------------->
<H3>The central game class: <em>KGame</em></H3>
When you want to develop your own KDE game using the KDE games library, you most likely want
to use the <em>KGame</em> class. There are two possible ways to extend it to your own needs:
Create a subclass and overwrite the virtual methods, or simply create an instance of KGame
and connect to the appropriate signals.<P>
<<more code about KGame, an easy example>>
<!-------------------------------------------------------------------------------->
<H3>Network games and related classes</H3>
One of the main principles in the design of <em>KGame</em> was to make network games possible
with a minimum of effort for the game developer.<P>
A network game is a game with usually several players, that are on different computers. These
computers are usually connected to the internet, and all the moves a player does are exchanged
over this network.<P>
The exchange of moves and other information is done using the class <em>KMessageServer</em>.
An object of this class is a server that waits for connections. Someone who wants to take part
in the game has to connect to this server - usually using an internet socket connection. He does
this by creating a <em>KMessageClient</em> object. This object connects to the message server.<P>
The transfer of data is realised by subclasses of the abstract class <em>KMessageIO</em>. One object
of this class is created on the client side, one on the server side. Different types of networks can
be supported by creating new subclasses of KMessageIO. There are already two subclasses of KMessageIO:
<em>KMessageSocket</em> uses a internet socket connection to transfer the data from the message client
to the message server or vice versa. <em>KMessageDirect</em> can be used if both the message server and
the message client are within the same process. The data blocks are copied directly to the other side,
so the transfer is faster and needs no network bandwidth.<P>
A typical network game situation could look like this:<P>
<IMG SRC="kmessageserver.png"><P>
Here, three KGame object (called message clients) are connected to the KMessageServer object. One
is in the same process, so it uses KMessageDirect. The other two use KMessageSocket, so an internet
socket connection is used. KGame doesn't talk directly to the message server, but uses a KMessageClient
object instead. One of the KMessageClient objects is the admin of the message server. This client has some
priviledges. It may e.g. kill the connection to other message clients, or limit the number of clients
that may connect.<P>
The KGame objects are by default all equal. So the usual approach will be that every KGame object will
store the complete status of the game, and any change or move will be broadcasted to the other KGame
objects, so that they all change the status in identical ways. Sometimes it may be necessary (or just
easier to implement) that one KGame object is a <em>game server</em> (i.e. he is repsonsible for everything,
he coordinates the complete game and stores the game status), whereas the other KGame objects are
only dumb stubs that are used to contact the <em>game server</em>. You can implement both approaches
using the message server structure. If you need to elect the KGame object that shall be
the game server, you may e.g. use the one that has the KMessageClient that is the admin of the message
server. (Of course this is only a suggestion, you can use other approaches.)<P>
The main principle when developing the message server/client structure was, that the message server
doesn't have <em>any</em> idea of the game and its rules that is played. The message server only forwards
messages from one message client to the others without interpreting or manipulating the data. So always
keep in mind that the message server is <em>not</em> a game server! It does not store any data about
the game status. It is only a server for network connections and message broadcasting, <em>not</em>
for game purposes. The reason for this principle is, that <em>any</em> game can be played using a
KMessageServer on any computer. The computer being the message server doesn't need to know anything
about the game that is played on it. So you don't have to install new versions of the game there. Only
the clients need to be game specific.<P>
Usually you don't need to create <em>KMessageServer</em> or <em>KMessageClient</em> objects in your game,
since <em>KGame</em> does this for you. There are three different scenarios fo network games that are
all supported in <em>KGame</em>:<P>
<b>Scenario 1: local game</b><P>
The local game should always be the default state a game should be in. To avoid having this scenario
as a special case, <em>KGame</em> automatically creates a KMessageServer object and a KMessageClient
object. So every change and every move is sent to the message server and is returned to the KGame
object before it is processed. Since the connection between the message client and the message server
uses KMessageDirect the data transfer is very fast and wont hurt in most cases.<P>
<IMG SRC="scenario0.png"><P>
This is the default situation right after creating the <em>KGame</em> object.<P>
<b>Scenario 2: network game, started by one player</b><P>
If one user is bored of playing alone, he can open his game for connections from the outside world.
He listens to a TCP/IP socket port (i.e. a number between 0 and 65535). Other players can create
KGame objects of their own and connect to this port. They need to know the IP address of that computer
and the port number. This situation will have this structure:
<IMG SRC="scenario1.png"><P>
The first player has to do something like:<P>
<PRE>
KGame *myGame = new KGame ();
// wait for connections on port 12345
myGame->offerConnections (12345);
</PRE>
And the other players have to do something like:<P>
<PRE>
KGame *myGame = new KGame ();
// connect to the message server
myGame->connectToServer ("theServer.theDomain.com", 12345);
</PRE>
This automatically removes the message server in these KGame objects and connects to the given
one instead.<P>
<b>Scenario 3: network game, using a stand alone message server</b><P>
Sometimes it is not possible to let the message server run on one of the players computer. If e.g. all
the players have their computer in a local network that uses masquerading to contact the internet,
other computers cannot connect to them since the computer doesn't have a IP address to the outside
world. Then the only way to play a network game is to have a standalone KMessageServer object on
another server computer (somthing like "games.kde.org" e.g.). Since the KMessageServer isn't game
specific at all, every game can be played using it. There doesn't have to be any special software
installed on that server computer, only the program creating a KMessageServer object.<P>
This scenario has some more advantages: The message server can be a well known meeting point to
start a game. This way one could play games against other players you never knew before. Furthermore
the game is stopped brutally when the program that contains the message server in scenario 2 is
quitted. (Migration of message servers is not yet implemented, but may be in the future.) Using a
stand alone message server, the players may enter and leave the game as they want.
<IMG SRC="scenario2.png"><P>
To create this scenario, a special KMessageServer program has to be started on the computer
that shall be the stand alone message server:<P>
<PRE>
% kmessageserver -port=12345
</PRE>
The other games that want to connect have to do this (supposed the stand alone message server
has the IP address "games.kde.org"):<P>
<PRE>
KGame *myGame = new KGame ();
// connect to the message server
myGame->connectToServer ("games.kde.org", 12345);
</PRE>
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