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Get up to speed with Apple’s 2D game framework
S Learn Sprite Kit for iOS Game Development will show you how to use Apple’s
E L
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T new framework to make a 2D gaming masterpiece.
TI e
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TE With Learn Sprite Kit for iOS Game Development, you’ll discover how easy it is a
RELA to create 2D games using the new Sprite Kit framework from Apple. You’ll find rn
out how simple it is to create a scene, add animated sprites, incorporate edges,
play sound effects, and create animated particles for special effects. You’ll also S
use touch events to control your sprites, implement the built-in physics engine, p
handle sprite collisions and contacts, and much more. r
i
To help you learn how to use all of these cool features of Sprite Kit, you’ll follow t
e
along as we build a complete 2D game for the iPhone. By the time you finish
this book, you’ll have made your own 2D game and you’ll have learned all that
K
you need to know to get started on your next masterpiece.
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With Learn Sprite Kit for iOS Game Development, you’ll learn how to do
the following: f
o
(cid:116) r
Add animated sprites to your game scene
(cid:116) i
Use TouchEvents to have your sprite react to touch input O
(cid:116)
Apply realistic physics to your game scene and characters S
(cid:116)
Handle sprite collisions and contacts with other game elements
(cid:116) G
Enhance game logic for sprite interaction, scoring, levels, and more
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This book is designed for beginning developers who have some understanding m
of object-oriented programming as well as intermediate iOS developers who
want to get up to speed quickly with Sprite Kit. e Learn
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Sprite Kit iOS
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Game Development
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Leland Long
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g
COMPANION eBOOK
ISBN 978-1-4302-6439-2
54999
Shelve in
Mobile Computing
SOURCE CODE ONLINE
User level:
www.apress.com Beginning–Intermediate 9781430264392
For your convenience Apress has placed some of the front
matter material after the index. Please use the Bookmarks
and Contents at a Glance links to access them.
Contents at a Glance
About the Author ...............................................................................................................xiii
About the Technical Reviewer ............................................................................................xv
Acknowledgments ............................................................................................................xvii
Introduction .......................................................................................................................xix
(cid:78) Chapter 1: Hello World .......................................................................................................1
(cid:78) Chapter 2: SKActions and SKTextures: Your First Animated Sprite .................................13
(cid:78) Chapter 3: Sprite Movement Responding to User Inputs .................................................29
(cid:78) Chapter 4: Edges, Boundaries, and Ledges .....................................................................49
(cid:78) Chapter 5: More Animated Sprites: “Enemies” and “Bonuses”.......................................77
(cid:78) Chapter 6: Creating a Cast of Characters ......................................................................103
(cid:78) Chapter 7: Points and Scoring .......................................................................................121
(cid:78) Chapter 8: Contacts and Collisions ................................................................................141
(cid:78) Chapter 9: Add More Scenes and Levels .......................................................................183
(cid:78) Chapter 10: Where to Go from Here ...............................................................................225
Index .................................................................................................................................227
v
Introduction
What This Book Is
This book serves as a guide to help you make your own iPhone game. The goal is to help you create
a simple 2D game from scratch using the new programming framework provided by Apple called
“Sprite Kit.” By using Sprite Kit to create your game, you will find that a lot of things that you would
normally have to code yourself handled for you. You’ll be amazed at how little code it takes to create
animated characters (sprites) that can interact with each other as they move around the screen.
As you work your way through this book, you will create a fairly simple (old-school style) 2D game for
the iPhone that allows users to control a character using their fingers on the touch screen. We’ll add
some bad guys to give the character certain challenges and some bonus items that users can collect
for extra points. We won’t deal with the complexity of screen scrolling (in order to keep it simple) and
instead will use a stationary screen, adding ledges so that the character can have some more space
in which to run around, rather than moving only along the bottom of the screen.
Each chapter is designed to highlight specific Sprite Kit features and basic game development
concepts, which will help you understand how to control or interact with those features and
concepts. When you’re finished with the book, you will have a broad understanding of what Sprite
Kit is all about, and you will have a cool game to play when you take a break from coding your
soon-to-be best-selling game.
Why Buy This Book
Why not just look through the awesome sample game called “Adventure” that Apple provides
for Sprite Kit developers to explore and examine? Because it can be complex and difficult for
beginners to dissect and understand. It is meant for more experienced game developers to
use, so that they can take their existing knowledge and use the new Sprite Kit APIs (Application
Programming Interface) to make their next game quicker and easier than ever before. I believe that
less experienced developers need something more straightforward as their introduction to Sprite Kit.
Start simple and move on to bigger and better game development once you understand the basics.
xix
xx Introduction
What You Need to Know
This book assumes that you have a basic understanding of how to create applications for the iPhone
using Xcode. You will not be spending any time learning programming styles or skills. You will be
focusing solely on making a game using Xcode as the tool. We assume that you can download,
install, and use the latest version of Xcode to create an application and run it on the iPhone Simulator.
What You Need to Have
In terms of hardware, you need an Intel-based Macintosh running Mountain Lion (OS X 10.8) or later.
Regarding software, you need Xcode 5.0 or later, since that is the first version to include the Sprite
Kit APIs. You can download Xcode from http://developer.apple.com.
What’s in This Book
Here is a brief overview of the chapters in this book:
n(cid:222)In Chapter 1, you’ll start with a template that gives you an intro screen and a
main game screen that will serve as the foundation for everything else that you
do with Spite Kit.
n(cid:222)In Chapter 2, you’ll add some basic physics so that your character doesn’t
just float around the screen. Then you’ll use some SKTextures for handling the
graphical side of the animation and some SKActions for handling the timing and
movement side of the animation.
n(cid:222)In Chapter 3, you’ll work with user interaction to drive character movement.
n(cid:222)In Chapter 4, we introduce some ideas about how you add environmental
objects with which your character can interact, like ledges to run along and
boundaries so that you can handle screen wrapping.
n(cid:222)In Chapter 5, you’ll add some bad guys and bonuses. We like bonuses!
n(cid:222)In Chapter 6, we’ll present one way to create a sort of “cast of characters” that
will handle the timing and spawning of bad guys and bonuses. You don’t want
everyone showing up on stage all at once!
n(cid:222)In Chapter 7, it’s all about points, as in a score! It’s all about the points, right?!
n(cid:222)In Chapter 8, you’ll work with sprite interaction. You don’t want your character
just running around the screen, “floating” right through the enemies and
obstacles, now do you?
n(cid:222)In Chapter 9, you’ll add more levels. You want the game to get progressively
harder as time goes on in order to keep it challenging and interesting, after all.
n(cid:222)In Chapter 10, we’ll wrap things up and point you where you can go from here to
make your game even more interesting and complex.
With all of these technical details out of the way, let’s get our hands dirty with some code! Turn the
page already! :)
1
Chapter
Hello World
We Love Games
“Waka waka waka!” (Pac-Man)
My teenage years were spent playing arcade games and watching other kids play video games.
Drop a quarter into the slot, and you were transported to a place that was awesome, feeling the
adrenaline rush as you dodged bad guys and avoided death, fingers flying all over the controls.
The best place to go was the nickel arcade, where you could pay a nominal admission fee and then
each game cost a single nickel! A ten-dollar bill could last you for hours!
When the money ran out and we had to snap back into the real world, we made games. My
computer had only 3KB of programmable memory, so they were very small games indeed.
No wasting code-space with comments—oh no! Variable names were single letters ($x was the most
common, of course). Ahhhh, those were the days!
Fast-forward 30 years and things have changed a bit. Major companies are creating games that
immerse you inside a 3D world complete with story lines that put novels to shame. Mobile devices
and desktop computers have more memory and graphics power than you could ever imagine back
in the day. However, even with all this power and complexity dominating the gaming world, you can
still find and enjoy games that are simple, easy on the eyes, and yet appealing due to the challenges
they present. We call them “old school games.” These games are not dead; they just reside in a
different category than the newest mega-games.
Tradition
As you’re probably aware, it has become somewhat of a tradition to call the first project in any
programming book “Hello World.” We wouldn’t want to break that tradition here, lest we offend your
programming finesse!
1
2 CHAPTER 1: Hello World
Setup
By now, you should have launched Xcode and be wondering where we will ask you to start. If you
haven’t yet launched Xcode, do so now.
From the Welcome to Xcode screen, you’ll need to choose Create a New Xcode Project or, if you
have already opened Xcode so that the Welcome screen is no longer visible, choose New Project
from the File menu.
From the New Project Template sheet (see Figure 1-1), make sure that iOS - Application is selected
from the list on the left, click on the Sprite Kit Game template icon, and then click the Next
button. Note that your choices might be slightly different if you have different components loaded.
PhoneGap, for example, is on the screen shown here, but it may not be the case on your display.
Figure 1-1. The project template selection sheet lets you select from various templates when creating a new project
Fill in the fields on the project details sheet, as shown in Figure 1-2. For Organization Name, enter
your name; as the Company Identifier, enter com.yourname.
CHAPTER 1: Hello World 3
Figure 1-2. The project details sheet. Use these settings for simplicity’s sake
These fields can be anything you want. We provided the data as an example, but be aware that
if you choose to enter other values than what we have suggested, your code will not match the
examples in the book. Also, when choosing what to enter, keep in mind that the generated bundle
identifier (shown in gray) needs to be URL-compliant and unique. We choose SKB as the class prefix
so that we can avoid naming conflicts with Apple (who reserves the use of all two-letter prefixes) and
other developers whose code we might use. For the projects in this book, we’re going to use the
prefix SKB, which stands for Sprite Kit Book.
After clicking the Next button, you’ll see the standard Save window, which allows you to choose
where to store your new project. It’s up to you whether you leave the Source Control checkbox
enabled or not. If you’re not familiar with what it is or how it works, feel free to uncheck it before
moving on. Make your choice, and then click the Create button when you’re ready.
Now that your new project has been created, saved, and opened, you will probably see some of the
target settings shown in Figure 1-3.
4 CHAPTER 1: Hello World
Figure 1-3. The project window. With the project selected on the left, you will see target details in the center pane
Using this template and Xcode’s default settings, go ahead and run the app—you know you want to!
After the build is completed, the Simulator should be launched and brought forward. The application
launch animation should then present and reveal the application in all its glory, as shown in Figure 1-4.
Figure 1-4. The iOS Simulator window. Your game is running!
CHAPTER 1: Hello World 5
What you see here is not just text on a screen. It’s not a standard UIView with a UILabel dropped
onto it inside a storyboard, as you are probably used to already when developing iPhone apps.
Instead, what we have here are four new objects that we will introduce to you.
The first object is the backdrop. It is an instance of an SKScene. Content in your game is organized
into scenes, which are represented by SKScene objects. The parent of this SKScene is an SKView,
which has an SKViewController as its controller.
The second object, SKLabelNode, has been dynamically created at runtime, not statically placed
there using Interface Builder. A font is assigned, a size is determined, its position is declared, and the
complete object is added as a child object into the scene.
The third object is an SKSpriteNode, built using an image file that’s been added to the project. The
point where the mouse or finger was pressed on the screen determines its position on the screen.
The fourth object is an SKAction, in this case, a rotation. The sprite object is told to run this action on
itself forever. The completed sprite object is then added to the scene as a child object.
As you’ve probably already deduced by the naming convention, these four objects are all part of the
Sprite Kit APIs. Needless to say, there are more than just these four objects to explore, but these
make for a nice introduction, so let’s continue.
You may be wondering about the extra information hanging out in the bottom right corner. These
are there at our request, and they can be turned on and off whenever the mood strikes. They can be
very useful as you begin to add more sprites to your scene, as they provide the details of the node
count and the current frame rate (measured in fps, or frames per second). You can use these values
to aid in determining the cause of possible sluggishness and game performance issues.
But wait, there’s more!
Click anywhere on the game screen. Well, that’s rather cool! A spinning spaceship should suddenly
appear from out of nowhere (see Figure 1-5). Click again in a different location. Yup, another
spaceship appears. If you’re insatiably curious, as most programmers are by nature, by now you are
clicking away all over the screen and there are spaceships spinning like crazy. Are you watching the
Nodes and FPS values as they change? How many nodes are visible before the frame rate drops
down to ugliness? Well, don’t forget that the simulator running on your lightning-fast Mac desktop
or laptop is a wee-bit faster than an actual iPhone, so don’t go assuming that you can have 3,000
sprites of gigantic proportions on the screen all at once and expect to have great frame rates when
your top-selling game is playing on an actual device. We’re just sayin. . .
