Multiplayer Game
Jaap MurreThis is a very simple chat ‘game’. Two ‘players’ are randomly matched and can then input text and send it to the other ‘player’ in a turn-taking manner. It is an example of how one could develop a full-fledged (economic) game with two or more players who interact over Internet.
On starting a ‘game’, the subject either has to wait for an ‘opponent’ or if one is already waiting, in which case the subject can start immediately with sending and receiving messages.
This script demonstrates how through use of the store_now() and receive() functions, it is possible to communicate between different sessions. That is, two subjects doing the same experiment can communicate by repeated checking a ‘secret variable’ (we use the timestamp to generate one), writing to it and reading it. Several such variables can be defined for a script.
The script also shows one way of assigning subjects in order of arrival.
The chat function is very basic and could be replaced by a more involved (economic) game, which could make use of the same communication functions developed in the Game class.
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function Game() {
this.receive_poll_interval = 1000; // ms
this.opponent_poll_interval = 1000; // ms
}
Game.prototype.wait_for_opponent = function() {
var opponent_waiting = retrieve('opponent_waiting','script');
if (!opponent_waiting) {
this.first = 1; // I was here first
store_now(true,'opponent_waiting','script');
this.game_id = 1*(new Date()); // 1* converts to number
store_now(this.game_id,'game_id','script');
while (true) {
if(!retrieve('opponent_waiting','script')) {
this.game_id = retrieve('game_id','script');
break;
} else {
await(this.opponent_poll_interval);
}
}
} else {
this.game_id = retrieve('game_id','script');
store_now(false,'opponent_waiting','script'); // Affirm by clearing
this.first = false; // I was second; someone was already waiting
}
}
// Sends content over (optional) named channel and waits until it has been received
Game.prototype.send = function(content,channel) {
content = {
data: content
}
content = JSON.stringify(content); // Ensure correct JSON-ification on server
channel = channel || "channel";
var id = channel + '_' + this.game_id,
signal;
store_now(content,id,'script');
while (true) {
signal = retrieve(id,'script');
if(signal) { // Wait until the signal has cleared, i.e., has been received
await(this.receive_poll_interval);
} else {
break;
}
}
}
// Receive content over (optionally) named channel. Waits until reception.
Game.prototype.receive = function(channel) {
channel = channel || "channel";
var id = channel + '_' + this.game_id,
signal;
while (true) {
signal = retrieve(id,'script');
if(signal) {
store_now(false,id,'script'); // clear channel; signals reception
return signal.data;
} else {
await(this.receive_poll_interval); // wait and try again
}
}
}
text("Waiting for opponent");
var game = new Game();
game.wait_for_opponent();
var first_turn = true;
while (true) { // Simple turn-taking chat
if (game.first && first_turn) { // first_turn helps determine who sends first
first_turn = false;
input("Send message","message");
game.send(response.message);
text("Message received");
} else {
text("Waiting for message")
var msg = game.receive();
text(msg);
await(5000);
input("Send message","message");
game.send(response.message);
text("Message received");
}
}