Retro Style Platform Runner Game for mobile with EaselJS (Part 1)

Editors Note: The tutorial is a little bit outdated now, but it still works. However if you would like to learn more on this topic and get a more detailed verison plus all the extras and resources, you should check out my ebook: From Zero to the Appstore - Blueprints for an HTML5 Game.

Here I’m starting a series of 4 articles on how to create a small game with EaselJS that “can” run on your mobile device (unfortunately it won’t run on all mobile devices) – however I also plan on a future posting on how to use technologies like cocoonJS to create a WELL-PERFORMING native app from this.

The FINAL result

The result is going to look similar to this (but with better code!) – In case you take a look at the source-code: This is NOT a good example on how to code cleanly – I did this as a quick mashup to try out a few things. – You can also do another jump, while in the air:

To test this on your mobile device, point your mobile browser to: http://demos.indiegamr.com/jumpy

The result of Part 1&Part 2

Let’s get started with the basics – Setting up the Stage

Working with EaselJS is pretty simple, especially when you worked with ActionScript3 before, as a lot of the methods and classes are based on ActionScript3-equivalents. So basically the first thing you have to do in order to see a result, is to create a canvas-element and set up the “Stage” here is how this can be done:

// creating the canvas-element
canvas = document.createElement('canvas');
canvas.width = 500;
canvas.height = 250;
document.body.appendChild(canvas);

// initializing the stage
stage = new Stage(canvas);

// creating the canvas-element

canvas = document.createElement('canvas');

canvas.width = 500;

canvas.height = 250;

document.body.appendChild(canvas);

// initializing the stage

stage = new Stage(canvas);

However, if you tried this out, it wouldn’t bring you that much of a result, because in order to actually see something the Stage has to be ‘updated’ (stage.update();) by EaselJS, also this is something, that has to be done every frame – so to do that, we can setup an event, that will update the Stage every frame.

Ticker.setFPS(30);
Ticker.addListener(tick);
function tick(e) {
	stage.update();
}

Ticker.setFPS(30);

Ticker.addListener(tick);

function tick(e) {

stage.update();

}

Great! Now we have a stage, that is updated with 30 frames/second.

More basics – Adding something to the stage

Now that we’ve setup the Stage, we can obviously still see nothing, because there is no object/image there to display.

The basic flow of doing this is to: 1) Preload an Image then 2) Create an DisplayObject with that image and finally 3) add this DisplayObject to the Stage(or another Container)

var img = new Image();
img.onload = onImageLoaded;
img.src = 'asset/myImage.png';

function onImageLoaded(e) {
	var myBitmap = new Bitmap(img);
	stage.addChild(myBitmap);
}

var img = new Image();

img.onload = onImageLoaded;

img.src = 'asset/myImage.png';

function onImageLoaded(e) {

var myBitmap = new Bitmap(img);

stage.addChild(myBitmap);

}

Preloading:
Some might ask here, why I’m not introducing PreloadJS to preload all the assets (or in this case: one asset) – well PreloadJS is a very nice way to do so – and I also recommend using it for some projects, but I tried running the app with the cocoonJS-launcher and receiveed a big load of Errors from cocoon(due to cocoon’s limited JS-parsing). Now this is NOT the fault of PreloadJS, however since preloading assets is nothing super-complicated, that requires super-extensive knowlege(basically one function), I chose to use an own 5-line implementation to achieve this.

Great! – So how do I make a game from this?

Well, a typical game usually needs the following things:

Part 1: User-Input (Keystrokes, MouseClick, Touch) & Movement
Part 2: Collisions between objects
Part 3: Animations

User Input

To listen to userinput-events we first have to distinguish if the device is a touch-device or has a regular screen and add the according event listeners.

//check for a touch-option
if ('ontouchstart' in document.documentElement) {
	canvas.addEventListener('touchstart', function(e) {
		handleKeyDown();
	}, false);

	canvas.addEventListener('touchend', function(e) {
		handleKeyUp();
	}, false);
} else {
	document.onkeydown = handleKeyDown;
	document.onkeyup = handleKeyUp;
	document.onmousedown = handleKeyDown;
	document.onmouseup = handleKeyUp;
}

function handleKeyDown(e)
{
	// execute things on KeyDown
	// e.g.
	hero.jump();
}

function handleKeyUp(e)
{
	// execute things on KeyUp
}

//check for a touch-option

if ('ontouchstart' in document.documentElement) {

canvas.addEventListener('touchstart', function(e) {

handleKeyDown();

}, false);

canvas.addEventListener('touchend', function(e) {

handleKeyUp();

}, false);

} else {

document.onkeydown = handleKeyDown;

document.onkeyup = handleKeyUp;

document.onmousedown = handleKeyDown;

document.onmouseup = handleKeyUp;

}

function handleKeyDown(e)

{

// execute things on KeyDown

// e.g.

hero.jump();

}

function handleKeyUp(e)

{

// execute things on KeyUp

}

This is pretty straight forward and should widely explain itself.

Movement

To create movement, the simples thing to do is e.g. to alter the position of an object a little bit every frame, just like this:

function tick(e) {
	//this will move the object down by 1 pixel
	myBitmap.y += 1;
	//this will update the stage
	stage.update();
}

function tick(e) {

//this will move the object down by 1 pixel

myBitmap.y += 1;

//this will update the stage

stage.update();

}

However in order to get the whole thing not too messy, once there are more objects involved in the scene, we should setup an own class for each object, or at least each object that is moving, as an example I put together the following:

(function (window) {
	function Hero(image) {
		this.initialize(image);
	}
 	Hero.prototype = new Bitmap();

 	// save the original initialize-method so it won't be gone after
 	// overwriting it
 	Hero.prototype.Bitmap_initialize = Hero.prototype.initialize;

 	// initialize the object
 	Hero.prototype.initialize = function (image) {
 		this.Bitmap_initialize(image);
 		this.name = 'Hero';
 		this.snapToPixel = true;
 	}

 	// we will call this function every frame to 
	Hero.prototype.tick = function () {
		this.y += 1;
 	}

 	// this will reset the position of the hero
 	// we can call this e.g. whenever a key is pressed
 	Hero.prototype.reset = function() {
 		this.y = 0;
 	}

 	window.Hero = Hero;
} (window));

(function (window) {

function Hero(image) {

this.initialize(image);

}

Hero.prototype = new Bitmap();

// save the original initialize-method so it won't be gone after

// overwriting it

Hero.prototype.Bitmap_initialize = Hero.prototype.initialize;

// initialize the object

Hero.prototype.initialize = function (image) {

this.Bitmap_initialize(image);

this.name = 'Hero';

this.snapToPixel = true;

}

// we will call this function every frame to

Hero.prototype.tick = function () {

this.y += 1;

}

// this will reset the position of the hero

// we can call this e.g. whenever a key is pressed

Hero.prototype.reset = function() {

this.y = 0;

}

window.Hero = Hero;

} (window));

With the Hero-class implemented, we can now create a hero object and apply some interaction, all together it would look like this:

if ('ontouchstart' in document.documentElement) {
	canvas.addEventListener('touchstart', function(e) {
	handleKeyDown();
	}, false);
} else {
	document.onkeydown = handleKeyDown;
	document.onmousedown = handleKeyDown;
}

var	stage,
	canvas,
	hero,
	img = new Image();

function init() {
	canvas = document.createElement('canvas');
	canvas.width = getWidth();
	canvas.height = getHeight();
	document.body.appendChild(canvas);

	stage = new Stage(canvas);

	img.onload = onImageLoaded;
	img.src = 'assets/hero.png';
}

function onImageLoaded(e) {
	hero = new Hero(img);
	stage.addChild(hero);
	hero.reset();

	Ticker.setFPS(30);
	Ticker.addListener(tick);
}

// move the hero down by 1px
// and update/render the stage
function tick() {
	hero.tick();
	stage.update();
}

// whenever a key is pressed then hero's
// position will set to y=0;
function handleKeyDown(e)
{
	hero.reset();
}

init();

if ('ontouchstart' in document.documentElement) {

canvas.addEventListener('touchstart', function(e) {

handleKeyDown();

}, false);

} else {

document.onkeydown = handleKeyDown;

document.onmousedown = handleKeyDown;

}

var stage,

canvas,

hero,

img = new Image();

function init() {

canvas = document.createElement('canvas');

canvas.width = getWidth();

canvas.height = getHeight();

document.body.appendChild(canvas);

stage = new Stage(canvas);

img.onload = onImageLoaded;

img.src = 'assets/hero.png';

}

function onImageLoaded(e) {

hero = new Hero(img);

stage.addChild(hero);

hero.reset();

Ticker.setFPS(30);

Ticker.addListener(tick);

}

// move the hero down by 1px

// and update/render the stage

function tick() {

hero.tick();

stage.update();

}

// whenever a key is pressed then hero's

// position will set to y=0;

function handleKeyDown(e)

{

hero.reset();

}

init();

here’s how it should look like(depending on the background-color, that you chose for your html-body):

Of course this is very basic, and the movement is absolutely not realistic, since there is no acceleration in the movement, but we can fix this by adding a velocity-object to the hero, just add the following:

//add this to the "initialize"-method
this.velocity = {x:0,y:12};

//now we update the "tick"-method with:
this.velocity.y += 1;
this.y += this.velocity.y;

//and this goes into the "reset"-method:
//getHeight() is a utility-function, but can also be
//replaced with a hardcoded-number
this.y = getHeight() / 1.25;
this.velocity.y = -15;

//add this to the "initialize"-method

this.velocity = {x:0,y:12};

//now we update the "tick"-method with:

this.velocity.y += 1;

this.y += this.velocity.y;

//and this goes into the "reset"-method:

//getHeight() is a utility-function, but can also be

//replaced with a hardcoded-number

this.y = getHeight() / 1.25;

this.velocity.y = -15;

and this is how it should look like by now:

Awesome, now we have a basic “game”, with a character falling down, that will be reset on any user-input. The next parts are going to cover collisions and animations.

You can download the source-files here: download

Agenda

Part 1: User-Input (Keystrokes, MouseClick, Touch) & Movement
Part 2: Collisions between objects
Part 3: Movement&More Collision
Part 4: Adjustments for mobile devices
Part 5: Polishing up the game with animations & eye candy

20 thoughts on “Retro Style Platform Runner Game for mobile with EaselJS (Part 1)”

yasin on July 1, 2012 at 2:43 pm said:

nice, good job! keep on going

Reply ↓
adude on July 2, 2012 at 9:43 pm said:

man, pretty cool tutorial!
really looking forward for the next ones!!

Reply ↓
Ludei on July 3, 2012 at 12:48 am said:

Olaf, nice tutorial. If you ever need first hand help regarding CocoonJS, please don’t hesitate to contact us at contact@ludei.com or in by submitting this form:
http://ludei.com/about

We would be glad to help!

Reply ↓
- olsn on July 3, 2012 at 8:04 am said:
  
  thanks! – absolutely will do that
  
  Reply ↓
Ludei on July 3, 2012 at 7:38 pm said:

Also,we are improving the script injection support, we are confident that frameworks like PreloadJS will be supported in CocoonJS in the near future. Right now we have document.createElement(“script”) support but the scripts must be added to the document body using document.body.appendChild.

Reply ↓
Pingback: Retro Style Plattform Runner Game for mobile with EaselJS (Part 2) | indiegamr
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Pingback: Retro Style Platform Runner Game for mobile with EaselJS (Part 4) – adjusting to mobile displays | indiegamr
Madhu Rakhal Magar on July 19, 2012 at 4:43 am said:

Simply Great,

I love the game a lot and the techniques that you use.

Reply ↓
Pingback: Retro Style Platform Runner Game for mobile with EaselJS (Part 5) – Animations and polishing | indiegamr
Lars on July 25, 2012 at 4:14 pm said:

Thanks for this helpful tutorial.

I’m looking now at keyboard input. It looks like you used DOM event handling — does EaselJS not provide help for keyboard events, like it does for mouse events?

Reply ↓
- olsn on July 25, 2012 at 4:20 pm said:
  
  Actually I don’t know about that – but good point!
  The main-goal for this was to run it also on a mobile device in which case keyboard&mouse are irrelevant
  But I will look it up and update the article. Thank you.
  
  Reply ↓
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Benny Neugebauer on January 27, 2013 at 8:39 pm said:

Nice tutorial. Thank you very much!

Reply ↓
Jake on March 15, 2013 at 9:14 pm said:

I wonder, where you able to handle EaselJs’s onPress events inside CocoonJS?

Reply ↓
- olsn on March 15, 2013 at 9:18 pm said:
  
  Yes, that worked. Although since EaselJS 0.6.0 is released I suggest you use .addEventListener() instead of .onPress (but both are still working)
  http://www.createjs.com/Docs/EaselJS/classes/EventDispatcher.html
  
  Reply ↓
Jake on March 15, 2013 at 10:21 pm said:

For some reason, neither is working for me at the canvas or DisplayObject level.
I’m using EaselJs 0.6.0 with the latest version of CocoonJS (downloaded today).

document.addEventListener(‘touchstart’,..) works, but the same call fails when performed on a canvas or a DisplayObject instance.

I tried also “click” instead of “touchstart”.

Do you have any suggestion what might cause it?

Reply ↓
Jake on March 15, 2013 at 11:15 pm said:

Well, after setting createjs.Touch.enable(stage), touchstart fires when registered on canvas level, still not on an individual DisplayObject though.

Reply ↓
- olsn on March 16, 2013 at 2:30 pm said:
  
  Hi Jake,
  
  yes I did not test this this on individual DisplayObjects, just on the Stage and I assumed that it would work on everything, but you are right, as it turns out this was not working. I tracked down the issue that was causing this problem and wrote a little quick fix for that, I’ll post it shortly.
  
  cheers
  
  Reply ↓
- olsn on March 16, 2013 at 2:41 pm said:
  
  Posted the fix here: http://indiegamr.com/quickfix-to-enable-touch-of-easeljs-displayobjects-in-cocoonjs/
  
  Reply ↓