Emanuele Feronato

Talking about Circle Chain game, Game development, HTML5 and Javascript.

When I celebrated the 1000th blog post, I told you I would have started to blog about HTML5 game development, and today I want to show you the classic Circle Chain engine made with CreateJS, a suite of Javascript libraries & tools for building rich, interactive experiences with HTML5.

Before I start with this tutorial, remember there’s an iPhone version of Circle Chain available for free in the App Store and I am going to release the Stencyl project for free once it reaches 1,000 downloads (415 to go).

Like all HTML5 projects, this Circle Chain prototype consist in an HTML part…

and a javascript part, fully commented:

// CreateJS features a Javascript library that lets you manage and co-ordinate
// the loading of assets, so we are going to use it
var preloader;
// manifest array will store every asset we need to preload, just like the
// manifest of a real world ship. As you can see, I am defining each manifest
// item with its relative path and an unique id
var manifest=[
	{src:"images/background.png", id:"background"},
	{src:"images/greencircle.png", id:"greenCircle"}
];
// the stage, the king of every game. 
var stage
// I need an array to store all my green circles, circleBitmap will do it
var circleBitmap = new Array();
// play function is the executed once the page loads
function play(){
	// first, I construct the stage as a Stage instance on the canvas id
	stage = new Stage(document.getElementById("canvas"));
	// then it's time to create the preloader
	preloader = new PreloadJS();
	// loadManifest is the method required to preaload all assets
	preloader.loadManifest(manifest);
	// and onComplete is the event trigger which will call loaded function
	preloader.onComplete = loaded;	
}
// loaded function will place all sprites on the stage and initialize the game
function loaded(event){
	// this is a variable I'll be using to assign a random direction to each
	// green circle
	var randomDirection;
	// look how I am picking up graphic assets from the preloader
	var bgImg=preloader.getResult("background").result;
	// once the background is picked up, I assign it to a Bitmap variable
     var bgBitmap = new Bitmap(bgImg);
     // then it's added to stage with addChild, just like AS3
	stage.addChild(bgBitmap);
	// the same concept is applied to the green circle, 10 times
     var circleImg=preloader.getResult("greenCircle").result;
     for(i=0;i<10;i++){
     	circleBitmap[i]=new Bitmap(circleImg);
     	// look at x and y properties
		circleBitmap[i].x=Math.random()*450+25-9;
		circleBitmap[i].y=Math.random()*450+25-9;
		// choosing a random direction
		randomDirection=Math.random()*2*Math.PI;
		// and defining xSpeed and ySpeed as custom properties
		circleBitmap[i].xSpeed=2*Math.cos(randomDirection);
		circleBitmap[i].ySpeed=2*Math.sin(randomDirection);
		// finally adding green circles to stage
		stage.addChild(circleBitmap[i]);
	}
	// look how I am setting the game to be 30fps!! So easy!!
	Ticker.setFPS(30);
	// and this is something like AS3 enter frame event, calling gameLoop
	// function at every tick
	Ticker.addListener(gameLoop);
}
function gameLoop(){
	// this loop just updates green circles position
	for(i=0;i<10;i++){
		circleBitmap[i].x+=circleBitmap[i].xSpeed;
		circleBitmap[i].y+=circleBitmap[i].ySpeed;
		if(circleBitmap[i].x>500-9){
			circleBitmap[i].x-=500;
		}
		if(circleBitmap[i].x<0-9){
			circleBitmap[i].x+=500;
		}
		if(circleBitmap[i].y>500-9){
			circleBitmap[i].y-=500;
		}
		if(circleBitmap[i].y<0-9){
			circleBitmap[i].y+=500;
		}
	}
	// at the end don't forget to update the stage to show what's going on
	stage.update();
}

as you can see, it's not that different than an AS3 script.

And this is the result:

Next time, I'll show you the complete game.