Game Client

Although the game is displayed on the big screen, players interact with their local game client. The game client provides the players with the form they use to create their character. Once the player is logged in, the JavaScript code executing within the game client's browser intercepts input in the form of keystrokes or clicks of buttons found on screen.

The input is passed asynchronously using AJAX to the server side code (PHP) that places it into the database. As mentioned previously, the game client framework requires a web browser that supports JavaScript and creation of asynchronous objects.

Figure 3. Flow of players' input into database.

Game Server

The complement to the game client framework is the game server. The game server consists of the game UI and the server code that retrieves player input from the database. While the game server code operates much like the game client code, only in reverse, the main hurdle to overcome with the game server was processing user input and updating the game shared screen with minimal delay.

In web applications, a common way to retrieve updates from the server using AJAX is to poll the server on a set interval. In our case, we had to create an environment where the players' input would seem to flow directly from the players' side to the shared game view as quickly as possible. Using an asynchronous call to poll the server would be inefficient because the asynchronous object is created each time we make a call to the server.

Instead, we put a small twist on the asynchronous call to make better use of the existing object. An asynchronous object goes through five states when making a call to the server, results are processed on the last state, and the object is destroyed. In our case, we created collaboration between the server script and the asynchronous object to retrieve results continuously.

On the server side, we created a script that retrieves players' input in a loop and flushes its output buffer on each iteration. Flushing the output buffer makes the current results available to the asynchronous object without waiting until it reaches its last state. Once the server side loop is done, the asynchronous object changes to its last and complete state where it does nothing more than destroy and recreate the asynchronous object. With this setup, we are able to simulate multiple calls to the server in order to retrieve players' input with a single asynchronous object.

Another major function of the game server is to maintain the game instance. The game server deals with game creation and destruction. The game instance identifier used by players is created by the game server and made available to players via the database. In addition, the game server processes the players' input after retrieving it from the database.