lib/rotjs-library/manual/pages/engine.html

<h2>Asynchronous game engine</h2>

<p>Client-side JavaScript is non-blocking: all long-running operations are asynchronous. The <code>ROT.Engine</code> loop is well suited for orchestrating the possibly-async coordination of various game actors.</p>

<p>To control a game loop, you add individual entities (called <em>actors</em>) to the engine. Every entity must implement the <code>getSpeed()</code> method (since it is fed to the built-in <a href="#scheduler">scheduler</a> and the <code>act()</code> method. Once the engine is started, it correctly calls the <code>act()</code> method on proper actors. It is possible to recursively stop (lock) the engine, should some operation (such as displaying a dialog or waiting for user input) block the execution. Once all lock levels are unlocked, the engine continues its execution.</p>

<div class="example">
var engine = new ROT.Engine();
var output = [];

/* sample actor: pauses the execution when dead */
var actor1 = {
	getSpeed: function() { return 100; },
	lives: 3,
	act: function() {
		output.push(".");
		this.lives--;
		if (!this.lives) { 
			engine.removeActor(actor1);
			engine.lock();              /* pause execution */
			setTimeout(unlock, 500);    /* wait for 500ms */
		}
	}
}
engine.addActor(actor1);

var unlock = function() {               /* called asynchronously */
	var actor2 = {
		getSpeed: function() { return 100; },
		act: function() {
			output.push("@");
			engine.removeActor(actor2);
		}
	}

	output = [];
	engine.addActor(actor2);            /* add second actor */
	engine.unlock();                    /* continue execution */
	SHOW(output.join(""));
}

engine.start();
SHOW(output.join(""));
</div>