HTML5 Games by Jacob Seidelin - Ebook | Scribd - The first knowledge sharing application in Vietnam

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This edition first published 2014

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About the Author

JACOB SEIDELIN is a freelance web developer with 15 years of experience working with back-end programming, graphics design, and front-end technology. When not working with clients he enjoys JavaScript and HTML5, web game development, and generally pushing the limit of what is possible in the browser. Thee results of his adventures in web development can be witnessed at his website at http://www.nihilogic.dk/.

Acknowledgments

I’d like to acknowledge a few people who helped in the making of this book. I want to thank my editors Sydney Argenta and Melba Hopper and the rest of the Wiley team. A big thanks to Andrew Wooldridge, my technical editor, whose keen eye for technical details kept me on my toes. It has been a pleasure working with all of you. Thanks also to the people who helped in the making of the first edition, Linda Morris, Brian Herrmann, and Charles Hutchinson.

I’d also like to extend my gratitude to the web development community in general for the never-ending inspiration and motivation. The same goes for the hard-working people at W3C, Khronos, and other organizations trying to make the Web a better place through open standards. Keep fighting the good fight.

Finally, thanks to my beautiful Ulla for the endless support and patience. Thank you for believing.

HTML5 Games

Table of Contents

Introduction

Who this book is for

What this book is about

Part I: Getting Started with HTML5 Games

Chapter 1: Gaming on the Web

Tracing the History of HTML5

Using HTML5 for Games

Canvas

Audio

WebSockets

Web Storage

WebGL

HTML5 and Flash

Creating Backward Compatibility

Using feature detection

Filling the gaps with polyfills

Building a Game

Summary

Chapter 2: Taking the First Steps

Understanding the Game

Swapping jewels

Matching three

Level progression

Identifying Game Stages

Splash screen

Main menu

Playing the game

High score

Creating the Application Skeleton

Setting up the HTML

Adding a bit of style

Loading the scripts

Creating a DOM helper module

Creating the Splash Screen

Working with web fonts

Styling the splash screen

Summary

Chapter 3: Going Mobile

Developing Mobile Web Applications

Write once, read many

The challenges of mobile platforms

Handling User Input on Mobile Devices

Keyboard input

Mouse versus touch

Adapting to Small Screen Resolutions

Creating scalable layouts

Controlling the viewport

Disabling user scaling

Creating Different Views

Creating the main menu

Adding screen modules

Using CSS media queries

Detecting device orientation

Adding a landscape style sheet

Developing for iOS and Android Devices

Placing web applications on the home screen

Getting the browser out of the way

Debugging Mobile Web Applications

Enabling the Safari debugger

Debugging on Android

Building Native Web Applications

PhoneGap

Future Mobile Platforms

Summary

Part II: Creating the Basic Game

Chapter 4: Building the Game

Creating the Game Board Module

Initializing the game state

Filling the initial board

Implementing the Rules

Validating swaps

Detecting chains

Refilling the grid

Swapping jewels

Summary

Chapter 5: Delegating Tasks to Web Workers

Working with Web Workers

Limitations in workers

What workers can do

Using Workers

Sending messages

Receiving messages

Catching errors

Shared workers

A prime example

Using Web Workers in Games

Creating the worker module

Keeping the same interface

Summary

Chapter 6: Creating Graphics with Canvas

Ways to Display Graphics on the Web

Bitmap images

SVG graphics

The canvas element

When to choose canvas

Drawing with canvas

Drawing shapes and paths

Using advanced strokes and fill styles

Using transformations

Adding text, images, and shadows

Managing the state stack

Drawing the HTML5 logo

Compositing

Accessing Image Data

Retrieving pixel values

Updating pixel values

Exporting image file data

Understanding security restrictions

Creating pixel-based effects

Summary

Chapter 7: Creating the Game Display

Tracking Load Progress

Adding a progress bar

Building the Game Screen

Drawing the board with canvas

Exiting the game

Pausing the game

Summary

Chapter 8: Interacting with the Game

Capturing User Input

Mouse events on touch devices

The virtual keyboard

Touch events

Input events and canvas

Using gamepads and controllers

Building the Input Module

Handling input events

Implementing game actions

Binding inputs to game functions

Summary

Chapter 9: Animating Game Graphics

Making the Game React

Animation timing

Animating the cursor

Animating game actions

Adding Points and Time

Creating the UI elements

Creating the game timer

Pausing the game

Awarding points

Game over

Summary

Part III: Adding 3D and Sound

Chapter 10: Creating Audio for Games

HTML5 Audio

Detecting audio support

Understanding the audio format wars

Finding sound effects

Using the audio Element

Controlling playback

Using audio on mobile devices

Working with Audio Data

Using the Web Audio API

Building the Audio Module

Preparing for audio playback

Playing sound effects

Stopping sounds

Cleaning up

Adding Sound Effects to the Game

Playing audio from the game screen

Summary

Chapter 11: Creating 3D Graphics with WebGL

3D for the Web

Where you can use WebGL

Getting started with WebGL

Debugging WebGL

Creating a helper module

Using Shaders

Variables and data types

Using shaders with WebGL

Uniform variables

Varying variables

Rendering 3D Objects

Using vertex buffers

Using index buffers

Using models, views, and projections

Rendering

Loading Collada models

Using Textures and Lighting

Adding light

Adding per-pixel lighting

Creating textures

Creating the WebGL display

Loading the WebGL files

Creating the jewel objects

Setting up WebGL

Rendering jewels

Animating the jewels

Using Third-Party WebGL Engines

Summary

Part IV: Local Storage and Multiplayer Games

Chapter 12: Local Storage and Caching

Storing Data with Web Storage

Using the storage interface

Building a storage module

Making the Game State Persistent

Saving the game data

Creating a High Score List

Building the high score screen

Storing the high score data

Displaying the high score data

Application Cache

The cache manifest

Summary

Chapter 13: Going Online with WebSockets

Using WebSockets

Connecting to servers

Communicating with WebSockets

Using Node on the Server

Installing Node

Creating an HTTP server with Node

Creating a WebSocket chat room

Summary

Introduction

“ALL THIS IS done in HTML5, by the way!” exclaimed Steve Jobs, the mind and face of the Apple success story, as he walked the audience through the new HTML5-powered ad system at the iPhone OS 4.0 Keynote, receiving cheers, laughs, and applause in return. The recent developments in open, standards-based web technologies are moving the web forward at an increasing pace, and Apple’s embrace of HTML5, including the blocking of Flash on all iOS devices, is just another symbol of the power of this movement. Although Apple’s love for HTML5 might in part be fueled by business motives, it is clear that the open web is on the move and exciting things are happening on an almost daily basis, making it an exciting time for web and game developers alike.

The world of web and game development wasn’t always this exciting, however. Building games for the browser could be a frustrating experience and has traditionally meant having to choose between using feature-rich plugin-based technologies or settling for a more low-tech approach, trying to fit the square peg of HTML and JavaScript into the round hole of game development. Disagreeing or downright broken implementations of various standards have only made the consistent and predictable environment of, for instance, Flash more appealing.

By opting for plugins like Flash, developers and game designers gain access to frameworks that are suitable for advanced game development, featuring dynamic graphics, sounds, and even 3D, but doing so also disconnects the game from the technologies surrounding it. Although technologies such as Flash, Java, and Silverlight all have means to communicate with the rest of the page, they remain isolated objects with limited capabilities for mixing with the surrounding content.

In contrast, using HTML, JavaScript, and CSS — the native building blocks of the web — means your game will fit naturally within the context of a web page, but with them comes other compromises, not the least of which is a lack of suitable elements and APIs. When the first editions of the HTML standard were published in the mid-1990s, it is doubtful that anyone had rich Internet applications in mind, and HTML’s document-centric nature meant that it was much more suitable for marking up pages of text and images than for application and game development. Even as these pages slowly became more and more interactive as JavaScript and the Document Object Model (DOM) evolved, graphics were still limited to static images and styled HTML elements, and audio was pretty much nonexistent. Only recently have the specifications for HTML5, CSS3, and other related standards evolved in the direction of actual applications, allowing developers to build experiences more akin to desktop applications than the traditional page-based web site. Naturally, these developments also apply to web games, and many of the recent advancements are a perfect fit for games and other interactive entertainment applications.

Who this book is for

HTML, JavaScript, and CSS are no longer limited to building web sites; web apps can be deployed on the web, as desktop widgets, and on mobile devices and many other places. If you are in any way interested in developing games for these targets and want to leverage your existing web development skills to do so, this is the book for you.

You probably already know a good deal about web development and have worked with HTML, CSS, and JavaScript previously. HTML5 Games is not a general guide to HTML5, and it does not teach you how to build web sites, so it is generally assumed throughout the book that you have some basic experience with traditional HTML and have at least heard of the new elements and APIs. Not all aspects of HTML5 are covered either, simply because they are not very relevant to games. You do not need to be an expert programmer, but you should have some experience with JavaScript. The new JavaScript APIs introduced with HTML5 are, of course, covered and explained, but it is otherwise expected that you have a good grasp of the language itself.

HTML5 Games is also not a book about game design. Many excellent books are available that deal with all conceivable aspects of game development more in depth than what this book can offer you. Trying to cover topics as diverse as artificial intelligence, physics simulation, and advanced graphics programming with enough detail to do them justice would leave little room to talk about HTML5 and web development. That being said, you don’t need any prior experience with game development, nor do you need to be a mathematician or a great artist to use this book. HTML5 Games stays in the shallow end in terms of game development theory, and any nontrivial math and programming concepts that are used are explained as they are introduced. An interest in games and web development, a bit of high school math, and the ability to create very basic graphics should get you through the book just fine.

What this book is about

HTML5 Games is about taking your skills in web development and applying them to game development. It doesn’t matter if you are a web developer looking to move into the game development field, a Flash game developer interested in the new open web technologies, or if you possess an entirely different goal, HTML5 Games shows you how to use the tools you already know to bridge the divide between traditional web sites and fun game experiences.

During the course of the book, you go through the development of a complete web game from the initial white page to the final product, ready to play in both the browser as well as on your iPhone or Android device. You see how to utilize new elements such as canvas and audio to make games that fit naturally in the context of the web without relying on plugins or ugly hacks. You learn how to add multiplayer functionality using Web Sockets and Node. js, how to store game data on the client with Web Storage, and how to manipulate graphics down to the pixel level using canvas. You also see how the game can easily be moved to mobile devices, taking advantage of touch input. In addition, you see how your applications can be made available offline with the new application cache. Finally, HTML5 Games examines the options available for deploying and distributing the finished game. When you finish the book, you will be able to take these lessons and apply them to your own projects, creating smashing web games that fully exploit today’s open web technologies.

Most of the code you will encounter throughout the book is available from the book’s companion web site, which you will find at www.wiley.com/go/html5games.com. From there, you can download an archive containing all the code for the example game as well as many smaller, independent examples. Inside the archive, you will find a folder for each chapter of the book. These folders contain the example web game as it exists at the end of each chapter. If the given chapter has any examples not related to the game, you will find those in a sub-folder called examples.

As you work your way through the book, I encourage you to try building the game from the ground up but if you prefer to just examine the sample code, that’s perfectly fine as well. In any case, I hope you will have fun.

Now, let’s get started. Game on.

Part I

Getting Started with HTML5 Games

Chapter 1 Gaming on the Web

Chapter 2 Taking the First Steps

Chapter 3 Going Mobile

Chapter 1

Gaming on the Web

In This Chapter

• Finding out what HTML5 is and where it came from

• Seeing HTML5 within the context of games

• Looking at important new features

• Enabling feature detection and dealing with legacy browsers

BEFORE I DIVE into code, I want to establish the context of the technology we use. In this first chapter, I discuss what HTML5 is as well as some of the history that led to the HTML5 specification.

One of the most interesting aspects of HTML5 is how game developers can profit from many of its new features. In this chapter, I introduce you to some of those features and give you a few quick examples of how to use them. I talk about the canvas element and WebGL and the huge improvement they make in creating dynamic graphics. I also cover the audio element and the added multiplayer possibilities created by the WebSocket specification.

Everybody likes new toys, but remember that in the real world, old and outdated browsers keep many users from taking advantage of these cutting-edge features. In this chapter, I discuss a few tools that can help you detect which features you can safely use as well as how you can use these feature tests to load appropriate fallback solutions when necessary.

Finally, I briefly introduce the puzzle game that I use throughout the rest of the book to take you through the creation of a complete HTML5 game.

Tracing the History of HTML5

HTML, the language of the web, has gone through numerous revisions since its invention in the early 1990s. When Extensible Markup Language (XML) was all the rage around the turn of the millennium, a lot of effort went into transforming HTML into an XML-compliant language. However, lack of adoption, browser support, and backward compatibility left the web in a mess with no clear direction and a standards body that some felt was out of touch with the realities of the web.

When the W3C finally abandoned the XHTML project, an independent group had already formed with the goal of making the web more suitable for the type of web applications you see today. Instead of just building upon the last specification, the Web Hypertext Application Technology Working Group (WHATWG) began documenting existing development patterns and non-standard browser features used in the wild. Eventually, the W3C joined forces with the WHATWG. The two groups now work together to bring new and exciting features to the HTML5 specification. Because this new specification more closely reflects how web developers already use the web, making the switch to HTML5 is easy, too. Unlike previous revisions, HTML5 doesn’t enforce a strict set of syntax rules. Updating a page can often be as easy as changing the document type declaration.

But what is HTML5? Originally, it referred to the latest revision of the HTML standard. Nowadays, it’s harder to define; the term has gone to buzzword hell and is now used to describe many technologies that aren’t part of the HTML5 specification. Even the W3C got caught up in the all-inclusiveness of HTML5. For a brief period, they defined it as including, for example, Cascading Style Sheets (CSS) and Scalable Vector Graphics (SVG). This only added to the confusion. Fortunately, the W3C backed away from that stance and went back to the original, stricter definition that refers only to the actual HTML5 specification. In a somewhat bolder move, the WHATWG simply dropped the numeral 5, renaming it simply HTML. This actually brings it much closer to reality, in the sense that specifications such as HTML are always evolving and never completely supported by any browser. In this book, I just use the term HTML for the most part. You can assume that any mention of HTML5 refers to the actual W3C specification called HTML5.

Using HTML5 for Games

Many features from the HTML5 specification have applications in game development, but one of the first features to gain widespread popularity was the canvas element. The visual nature of this element without a doubt helped it spread quickly when the first interactive animations and graphics effects started appearing. More advanced projects soon followed, giving the new standard a dose of good publicity and promising a future with a more dynamic and visually interesting web.

Canvas

Hobbyist game developers were also among the first to embrace HTML5, and for good reason. The canvas element provides web game developers with the ability to create dynamic graphics, giving them a welcome alternative to static images and animated GIFs.

Sure, people have created more or less ingenious (and/or crazy) solutions in lieu of better tools for creating dynamic graphics. Entire drawing libraries rely on nothing more than colored div elements—that may be clever, but that approach isn’t sufficient for doing anything more than drawing a few simple shapes.

Uniform Resource Identifier (URI) schemes let you assign source files to img elements, for example, using a base64-encoded data string, either directly in the HTML or by setting the src or href property with JavaScript. One of the clever uses of this data URI scheme is to generate images on the fly and thus provide a dynamically animated image, which isn’t a great solution for anything but small and simple images.

Wolf 5K, the winner of the 2002 The 5K contest, which challenged developers to create a website in just five kilobytes, used a somewhat similar technique. The game, a small 3D maze game, generated black and white images at runtime and fed them continuously to the image src property, relying on the fact that img elements can also take a JavaScript expression in place of an actual URL.

Graphics drawn on a canvas surface can’t be declared with HTML markup; instead, they must be drawn with JavaScript using a simple Application Programming Interface (API). Listing 1-1 shows a basic example of how to draw a few simple shapes. Note that the full API provides much more functionality than the small portion shown in this example.

Listing 1-1 Drawing shapes with the canvas API

mycanvas>

var canvas = document.getElementById(mycanvas),

ctx = canvas.getContext(2d);

canvas.width = canvas.height = 200;

// draw two blue circles

ctx.fillStyle = blue;

ctx.beginPath();

ctx.arc(50, 50, 25, 0, Math.PI * 2, true);

ctx.arc(150, 50, 25, 0, Math.PI * 2, true);

ctx.fill();

// draw a red triangle

ctx.fillStyle = red;

ctx.beginPath();

ctx.moveTo(100, 75);

ctx.lineTo(75, 125);

ctx.lineTo(125, 125);

ctx.fill();

// draw a green semi-circle

ctx.strokeStyle = green;

ctx.beginPath();

ctx.scale(1, 0.5);

ctx.arc(100, 300, 75, Math.PI, 0, true);

ctx.closePath();

ctx.stroke();

The code produces the drawing shown in Figure 1-1.

Figure 1-1: This simple canvas drawing was created with JavaScript.

9781118855386-fg0101.tif

I revisit the canvas element in Chapter 6 and explore it in detail when I use it to create game graphics and special effects.

Audio

The new audio element is just as welcome to a web game developers’ toolbox as the canvas element. Finally, you have native audio capabilities in the browser without resorting to plug-ins. Not too long ago, if a website had audio, some form of Flash was involved. Libraries like the SoundManager 2 project (www.schillmania.com/projects/soundmanager2) provide full JavaScript access to most of the audio features of Flash. But even if such a bridge allows your own code to stay on the JavaScript side, your users still need to install the plug-in. The HTML5 audio element solves this problem, making access to audio available in browsers out of the box using only plain old HTML and JavaScript.

The audio element still has a few unresolved issues, however. The major browser vendors all seem to agree on the importance of the element and have all adopted the specification, but so far they’ve failed to agree on which audio codecs should be supported. So, while the theory of the audio element is good, reality has left developers with no other option than to provide audio files in multiple formats to appease all the browser vendors.

The audio element can be defined in the mark-up or created dynamically with JavaScript. (The latter option is of more interest to you as an application and game developer.) Listing 1-2 shows a basic music player with multiple source files, native user interface (UI) controls, and a few keyboard hotkeys that use the JavaScript API.

Listing 1-2 A simple music player with HTML5 audio

myaudio>

Prelude In E Minor, Op. 28.ogg/>

Prelude In E Minor, Op. 28.mp3/>

var audio = document.getElementById(myaudio);

document.onkeydown = function(e) {

if (e.keyCode == 83) {

audio.pause(); // Key pressed was S

} else if (e.keyCode == 80) {

audio.play(); // Key pressed was P

}

};

Tip

The W3C is currently working on expanding HTML5 with the Web Audio API, which enables advanced audio synthesizing and processing. Because this API is still experimental, I won’t be using it for the game in this book, although I briefly examine the possibilities it presents in Chapter 10 when I dive into HTML5 audio.

WebSockets

Ajax and the XMLHttpRequest object at its heart brought new life to the web with the Web 2.0 explosion in the early 2000s. Despite the many great things it has enabled, however, it is still painfully limited. Being restricted to the HTTP protocol, the action is rather one-sided, as the client must actively ask the server for information. The web server has no way of telling the browser that something has changed unless the browser performs a new request. The typical solution has been to poll the server repeatedly, asking for updates, or alternatively to keep the request open until there is something to report. The umbrella term Comet (http://en.wikipedia.org/wiki/Comet_(programming)) is sometimes used to refer to these techniques. In many cases, that is good enough, but these solutions are rather simple and often lack the flexibility and performance necessary for multiplayer games.

Enter WebSockets. With WebSockets, you’re a big step closer to the level of control necessary for efficient game development. Although it isn’t a completely raw socket connection, a WebSocket connection does allow you to create and maintain a connection with two-way communication, making implementation of real-time multiplayer games much easier. As Listing 1-3 demonstrates, the interface for connecting to the server and exchanging messages is quite simple.

Listing 1-3 Interacting with the server with WebSockets

// Create a new WebSocket object

var socket = new WebSocket(ws://mygameserver.com:4200/);

// Send an initial message to the server

socket.onopen = function () {

socket.send(Hello server!);

};

// Listen for any data sent to us by the server

socket.onmessage = function(msg) {

alert(Server says: + msg);

};

Of course, using WebSockets requires that you also implement a server application that’s compatible with the WebSockets protocol and capable of responding to the messages you send to it. This doesn’t have to be a complex task, however, as I show you in Chapter 13 when you build a simple chat application using WebSockets and Node.js.

Web Storage

Cookies are the usual choice when web applications need to store data on the client. Their bad reputation as spyware-tracking devices aside, cookies have also given developers a much-needed place to store user settings and web servers a means of recognizing returning clients, which is a necessary feature for many web applications because of the stateless nature of the HTTP protocol.

Originally a part of HTML5 but later promoted to its own specification, Web Storage can be seen as an improvement on cookies and can, in many cases, directly replace cookies as a larger storage device for key-value type data. There is more to Web Storage than that, however. Whereas cookies are tied only to the domain, Web Storage has a local storage that’s similar to cookies and a session storage that’s tied to the active window and page, allowing multiple instances of the same application in different tabs or windows. Unlike cookies, Web Storage lives on only the client and isn’t transmitted with each HTTP request, allowing for storage space measured in megabytes instead of kilobytes.

Having access to persistent storage capable of holding at least a few megabytes of data comes in handy when you want to store any sort of complex data. Web Storage can store only strings, but if you couple it with a JavaScript Object Notation (JSON) encoder/decoder, which is natively available in most browsers today, you can easily work around this limitation to hold structures that are more complex. In the game that you develop during the course of this book, you use local Web Storage to implement a Save Game feature as well as to store local high score data.

Listing 1-4 shows the simple and intuitive interface to the storage.