Learning Libgdx Game Development

By Andreas Oehlke

In Detail

Game development is a field of interdisciplinary skills, which also makes it a very complex topic in many respects. One decision that usually needs to be made at the beginning of a game development processis to define the kind of computer system or platform the game will be developed for. This does not pose any problems in general but as soon as the game should also be able to run on multiple platforms it will become a developer's nightmare to maintain several distinct copies of the same game. This is where the libGDX multi-platform game development framework comes to the rescue!

"Learning Libgdx Game Development" is a practical, hands-on guide that provides you with all the information you need to know about the libGDX framework as well as game development in general so you can start developing your own games for multiple platforms. You will gradually acquire deeper knowledge of both, libGDX and game development while you work through twelve easy-to-follow chapters.

"Learning Libgdx Game Development" will walk you through a complete game development cycle by creating an example game that is extended with new features over several chapters. These chapters handle specific topics such as organizing resources, managing game scenes and transitions, actors, a menu system, using an advanced physics engine and many more. The chapters are filled with screenshots and/or diagrams to facilitate comprehension.

"Learning Libgdx Game Development" is the book for you if you want to learn how to write your game code once and run it on a multitude of platforms using libGDX.

Approach

A clear and practical guide to building games in libGDX.

Who this book is for

This book is great for Indie and existing game developers, as well as those who want to get started with game development using libGDX. Java game knowledge of game development basics is recommended.

• Language: English
• Publisher: Packt Publishing
• Release date: Sep 23, 2013
• ISBN: 9781782166054

Andreas Oehlke

Andreas Oehlke is a professional software engineer and a computer scientist who feels very much at home on any Linux/Unix machine. He holds a Bachelor's degree in Computer Science and loves to assemble and disassemble software and hardware alike. An exorbitant affinity for electronics and computers has always been his trademark. His hobbies include game and web development, programming in general (software design and new languages), programming embedded systems with microcontrollers, playing sports, and making music. He currently works full-time as a software engineer for a German financial institution. Furthermore, he has worked as a consultant and a game developer in San Francisco, CA. In his spare time, he provides his expertise to a German startup called Gamerald (http://www.gamerald.com/).

Book preview

Table of Contents

Learning Libgdx Game Development

Credits

About the Author

About the Reviewers

www.PacktPub.com

Support files, eBooks, discount offers and more

Why Subscribe?

Free Access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Errata

Piracy

Questions

1. Introduction to Libgdx and Project Setup

Diving into Libgdx

Features of Libgdx 0.97

Graphics

Audio

Input Handling

File I/O

Math and Physics

Utilities

Tools

Getting in touch with the community

Prerequisites for installing and configuring

Java Development Kit (JDK)

Eclipse – Integrated Development Environment (IDE)

Downloading Libgdx

Installing Android SDK

Running Eclipse and installing plugins

Creating a new application

Kicking your game to life

Key to success lies in planning

Game project – Canyon Bunny

Description of the game

Summary

2. Cross-platform Development – Build Once, Deploy Anywhere

The demo application – how the projects work together

Backends

LWJGL (Lightweight Java Game Library)

Android

WebGL

Modules

The application module

Logging

Shutting down gracefully

Persisting data

Querying the Android API Level

Querying the platform type

Querying memory usage

Graphics module

Querying delta time

Querying display size

Querying the FPS (frames per second) counter

Audio module

Sound playback

Music streaming

Input module

Reading the keyboard/touch/mouse input

Reading the accelerometer

Starting and canceling vibrator

Catching Android soft keys

The files module

Getting an internal file handle

Getting an external file handle

The network module

HTTP GET and HTTP POST

Client/server sockets

Opening a URI in a web browser

Libgdx's Application Life-Cycle and Interface

Starter Classes

Running the demo application on a desktop

Running the demo application on Android

Running the demo application in a WebGL-capable web browser

The demo application – time for code

Inspecting an example code of the demo application

The create() method

The render() method

The dispose() method

Having fun with the debugger and Code Hot Swapping

Summary

3. Configuring the Game

Setting up the Canyon Bunny project

Using a class diagram for Canyon Bunny

Laying foundations

Implementing Constants

Implementing CanyonBunnyMain

Implementing WorldController

Implementing WorldRenderer

Putting it all together

Building the game loop

Adding test sprites

Adding game world's debug controls

Adding CameraHelper

Adding camera debug controls using CameraHelper

Summary

4. Gathering Resources

Setting a custom Android application icon

Creating texture atlases

Loading and tracking assets

Organizing assets

Testing assets

Handling level data

Summary

5. Making a Scene

Creating game objects

The rock object

The mountains object

The water overlay object

The clouds object

Implementing the level loader

Assembling the game world

Implementing the game GUI

The GUI score

The GUI extra lives

The GUI FPS counter

Rendering the GUI

Summary

6. Adding the Actors

Implementing the actor game objects

Creating the gold coin object

Creating the feather object

Creating the bunny head object

Updating the rock object

Completing the level loader

Adding the game logic

Adding collision detection

Losing lives, game over, and fixing the camera

Adding the game over text and the feather icon to the GUI

Summary

7. Menus and Options

Managing multiple screens

Exploring Scene2D (UI), TableLayout, and skins

Using Libgdx's scene graph for the menu UI

Building the scene for the menu screen

Adding the background layer

Adding the objects layer

Adding the logos layer

Adding the controls layer

Adding the Options window layer

Building the Options window

Using the game settings

Summary

8. Special Effects

Creating complex effects with particle systems

Adding a dust particle effect to the player character

Moving the clouds

Smoothing with Linear interpolation (Lerp)

Letting the rocks float on the water

Adding parallax scrolling to the mountains in the background

Enhancing the game screen's GUI

Event – player lost a life

Event – score increased

Summary

9. Screen Transitions

Adding the screen transition capability

Implementing transition effects

Knowing about interpolation algorithms

Creating a fade transition effect

Creating a slide transition effect

Creating a slice transition effect

Summary

10. Managing Music and Sound Effects

Playing back music and sound effects

Exploring the Sound interface

Exploring the Music interface

Accessing the audio device directly

Exploring the AudioDevice interface

Exploring the AudioRecorder interface

Using sound generators

About the sfxr generator

About the cfxr generator

About the bfxr generator

Adding music and sounds to Canyon Bunny

Summary

11. Advanced Programming Techniques

Simulating physics with Box2D

Exploring the concepts of Box2D

Understanding rigid bodies

Choosing body types

Using shapes

Using fixtures

Simulating physics in the world

Physics body editor

Preparing Canyon Bunny for raining carrots

Adding the new assets

Adding the carrot game object

Adding the goal game object

Extending the level

Letting it rain carrots

Working with shaders in Libgdx

Creating a monochrome filter shader program

Using the monochrome filter shader program in Canyon Bunny

Adding alternative input controls

Summary

12. Animations

Manipulating actors through actions

Actions for manipulating actors

Controlling the order and time of execution

Animating the menu screen

Animating the gold coins and bunny head actors

Animating the menu buttons and options window

Using sequences of images for animations

Packing animations using the texture packer

Choosing between animation play modes

Animating the game screen

Defining and preparing new animations

Animating the gold coin game object

Animating the bunny head game object

Summary

Index

Learning Libgdx Game Development

---

Learning Libgdx Game Development

Copyright © 2013 Packt Publishing

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First published: September 2013

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Cover Image by Aniket Sawant (<[e-mail]>)

Credits

Author

Andreas Oehlke

Reviewers

Ebenezer Edelman

Matthias Markowski

David Saltares Márquez

Chris Moeller

Acquisition Editors

Kartikey Pandey

Julian Ursell

Lead Technical Editor

Mayur Hule

Technical Editors

Menza Mathew

Amit Shetty

Harshad Vairat

Copy Editors

Mradula Hegde

Gladson Monteiro

Sayanee Mukherjee

Kirti Pai

Adithi Shetty

Project Coordinator

Apeksha Chitnis

Proofreaders

Paul Hindle

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Indexer

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Graphics

Abhinash Sahu

Production Coordinator

Shantanu Zagade

Cover Work

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About the Author

Andreas Oehlke is a professional software engineer and a computer scientist who feels very much at home on any Linux/Unix machine. He holds a Bachelor's degree in Computer Science and loves to assemble and disassemble software and hardware alike. An exorbitant affinity for electronics and computers has always been his trademark. His hobbies include game and web development, programming in general (software design and new languages), programming embedded systems with microcontrollers, playing sports, and making music.

He currently works full-time as a software engineer for a German financial institution. Furthermore, he has worked as a consultant and a game developer in San Francisco, CA. In his spare time, he provides his expertise to a German startup called Gamerald (http://www.gamerald.com/).

I want to thank my parents, Michael and Sigrid, and my brother Dennis for their constant and invaluable support, which definitely kept me on the go while writing this book. I also want to thank my close friends for giving me lots of helpful feedback, notably Sascha Björn Bolz with regard to providing the artwork for Canyon Bunny. Last but not least, I want to thank Klaus keith303 Spang for providing the music track as well as the whole team from Packt Publishing, including all the numerous reviewers involved, for 
their great work in producing a high quality book.

About the Reviewers

Ebenezer Edelman is a British computer programmer currently living in South Africa. He has an eclectic and diverse set of interests ranging from technology, engineering, and science to literature, photography, videography, and music. His hobbies include playing the piano, designing rocket engines, and occasionally a game of chess.

He started game development by learning C from the manual of a C compiler and developing simple text-based games. Then, after getting to grips with C++ and the DirectX SDK, he attempted to develop a 3D physics sandbox game, which never got past the beta stage. After that, he learned C# and the XNA framework and made several 2D games before deciding to get involved in mobile game development. He did this using Java and the LibGDX framework, which he used to get some of his old 2D games to Android. He is constantly looking to broaden his knowledge, and he now uses Research In Motion's open source C++ game engine gameplay3d.

In addition, he has experience of Windows Forms (C#), the GTK+ toolkit (Vala), the Qt toolkit (C++), the Android SDK (Java), as well as the x86 Assembly language, Python, PHP, JavaScript, and HTML/CSS.

His personal website and blog is located at http://EbenezerEdelman.tk/, and he is on Twitter (@EbenezerEdelman) and Google Plus (+EbenezerEdelman).

Matthias Markowski is a passionate game developer and video game enthusiast who focuses on the field of Graphics Programming. He began his professional career in 2005 through his involvement in the demoscene. He has contributed to the development of the fast-paced action MMOG (Massively Multiplayer Online Game) Black Prophecy and the Wii U casual game Your Shape Fitness Evolved 2013. He is currently employed at Ubisoft Blue Byte, known as a creator of excellent strategy games, located in Düsseldorf, Germany.

You can view his portfolio and contact details at http://mmarkowski.carbonmade.com.

David Saltares Márquez works at the award-winning developer Crytek as a games programmer. The Nottingham-based studio of the company behind the Crysis series was his jump into the AAA industry in 2012. Since then, he has been part of the Artificial Intelligence team, developing behaviors, pushing character fidelity forward, and developing systems that are now part of CryENGINE.

He obtained his BSc in Computing Science from Cádiz University (Spain) where he founded the games development society (ADVUCA) in collaboration with other passionate classmates. Through the society, he organized several talks and workshops with a strong focus on open source software, all of which were a great success.

By always working on side projects, he the joined the Libgdx community, attracted by the richness of its features, open source nature, multiplatform capabilities, and the hospitality of its developers. Libgdx allowed him to create various games such as Freegemas (https://github.com/siondream/freegemas-gdx) and Math Maze (http://siondream.com/blog/games/math-maze/). In return, he contributed to the maps' API and is very active on the forums.

Further information is available on his blog (http://siondream.com), where he talks in depth about Libgdx, programming, personal projects, and his experience in game jams such as Ludum Dare (http://siondream.com/blog/game-jams/).

Chris Moeller is a founder of the game studio Ackmi Design and Engineering. He has been building computers since the age of nine and has been programming for more than 10 years. He had the opportunity to work for software companies as a PHP developer, Java QA engineer, and Flash developer, and he currently works primarily for Android. He has been an enthusiastic gamer for most of his life and has created many game prototypes as well as several finished games. He writes game tutorials on his blog at www.chrismweb.com, and most of his new games can be found through his company website at www.ackmi.com, which he runs with his wife, Megan.

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Preface

Since personal computers have conquered our private homes, video games have become more and more popular and eventually a multimillion dollar business for big video game companies. With the introduction of mobile devices such as smartphones and tablets, the market for video games has experienced another significant increase; in particular, it has now become open to independent game developers with small budgets.

For game developers, it is essential to have tools at hand that provide fundamentals which allow rapid prototyping and cost-effective implementation of their creative ideas. This is where Libgdx comes into play.

Libgdx, as a Java-based game development framework, provides a unified access layer to handle all the supported platforms. Libgdx also makes use of C/C++ to achieve cross-platform support as well as to boost the application performance for mission critical tasks.

This book will show you how easy it is to develop cross-platform games by walking you through a complete game development cycle using the free and open source library Libgdx. Besides this, you will also learn about common game structure and the involved requirements.

You will be introduced to the key features of Libgdx and you will learn how to develop a game with ease and speed up your development cycles. In ten easy-to-follow chapters, you are going to develop your first Libgdx cross-platform game and add more and more game functionalities as you progress further through this book.

The special features will also make you acquainted with advanced programming techniques such as animations, physics simulations, and shader programs that enhance your games in both their gameplay and visual presentation.

By the end of this book, you will have a fully working 2D game that will run on Windows, Linux, Mac OS X, WebGL-capable browsers, and Android. You will also have all the skills required to extend the game further or to start developing your own cross-platform games.

What this book covers

Chapter 1, Introduction to Libgdx and Project Setup, covers how to install and configure the development environment and introduces you to the project setup tool that comes with Libgdx. Then, we will take a first look at the basics of what a game needs to come alive.

Chapter 2, Cross-platform Development – Build Once, Deploy Anywhere, explains the supported target platforms and how to deploy and run our application on each platform using a demo application. For the first overview of Libgdx's API, we will take a glance at each module. Then, the Application Cycle will be introduced, and we will take a look at how to debug and manipulate our code at runtime.

Chapter 3, Configuring the Game, brings us from our demo application to a real game by setting up a new project called Canyon Bunny. We will work on this project throughout the rest of the book and extend it from chapter to chapter with new features. Since Libgdx is a framework, we will first have to build our program architecture by using UML class diagrams to structure our game engine.

Chapter 4, Gathering Resources, describes how to gather all the resources (assets) needed for Canyon Bunny including graphics, audio files, level data, and so on. We will also find out how to load, track, and organize assets efficiently. Finally, it is time to think about how level data is going to be handled so that we are able to populate our game world with objects.

Chapter 5, Making a Scene, covers how to start implementing the first game objects such as rocks, mountains, and clouds, and how to use the assets that we added in Chapter 4, Gathering Resources. In order to visualize the game scene, a level loader is needed to put our game objects in their right places in the game world. Typically, games have a user interface to give feedback about their current status, so we will add a game GUI to Canyon Bunny that displays the player's high score, remaining extra lives, and so on.

Chapter 6, Adding the Actors, explains how to add the remaining game objects for Canyon Bunny, including the player character and collectible items to complete our game. We will also add simple physics for player movement and basic collision detection. Additionally, the game logic will be extended so that it is able to detect the life lost and game over conditions.

Chapter 7, Menus and Options, describes how to create a menu system with widgets such as buttons, labels, and checkboxes to enrich the overall game experience. Furthermore, we will add an Options window where the player can adjust the game settings.

Chapter 8, Special Effects, covers how to make use of particle systems and how to apply interpolation algorithms to create impressive effects such as dust clouds; a smooth, following camera; floating rocks; and parallax scrolling for mountains in the background. Using special effects will spice up the appearance of your game.

Chapter 9, Screen Transitions, introduces screen transitions. We will dive into enhanced visual effects using OpenGL's Framebuffer Objects for offscreen rendering into video memory. This will allow us to create seamless transitions for an improved user experience when switching from one screen to another. For Canyon Bunny, we will create a variety of transition effects.

Chapter 10, Managing Music and Sound Effects, will walk you through a list of recommended sound generators and discuss their differences. Then, we will take a look at Libgdx's Audio API and demonstrate how to use it by creating an audio manager. We do this so that handling all our audio playback needs become a breeze.

Chapter 11, Advanced Programming Techniques, introduces you to some advanced programming techniques that will guide you to the next level of game programming. We will build up basic knowledge about the Box2D API that enables us to create believable physics simulations in games. Additionally, we will discuss the topic of shader programs using the example of a monochrome image filter effect. Lastly, we will show you how to make use of the accelerometer hardware commonly available in modern smartphones and tablets, which allows controlling the game by tilting the device.

Chapter 12, Animations, explains how to polish up the game by adding animations. We will cover two different approaches to animate the game menu and the game world. Finally, we will implement a state machine to allow event-based animations for the player character.

What you need for this book

Libgdx is a cross-platform game development framework. For development, you will need a computer running either Windows (Vista/7/8), Linux (for example, Ubuntu), or Mac OS X (10.5+).

Additionally, you will need to download the Libgdx framework for game development. You can download Libgdx from https://code.google.com/p/libgdx/downloads/list. Please download Version 0.9.7 of Libgdx, as this is the version that is used in this book.

The Integrated Development Environment (IDE) used in this book is Eclipse. You can download the Eclipse IDE from http://www.eclipse.org/.

To develop games for the Android platform, you will need an Android device running Android 2.2 (Froyo) or higher and the official Android Software Development Kit (SDK) that can be downloaded from http://developer.android.com/sdk/index.html.

Who this book is for

This book is written for software developers who are new to game development and to Libgdx in particular. It is assumed that you have some experience in Java to be able to follow the discussed code in this book.

Conventions

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text are shown as follows: The main class of the demo application is MyDemo.java.

A block of code is set as follows:

@Override

public void dispose() {

  batch.dispose();

  texture.dispose();

}

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

public void update (float deltaTime) {   updateMotionX(deltaTime);   updateMotionY(deltaTime);

 

 

  // Move to new position   position.x += velocity.x * deltaTime;   position.y += velocity.y * deltaTime;

 

}

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: A new tab titled Development Mode should open at the bottom.

Note

Warnings or important notes appear in a box like this.

Tip

Tips and tricks appear like this.

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Errata

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Questions

You can contact us at <[e-mail]> if you are having a problem with any aspect of the book, and we will do our best to address it.

Chapter 1. Introduction to Libgdx and Project Setup

This book will take you on an exciting tour to show and teach you about game development using the open source Libgdx framework. Actually, you have chosen just the right time to read about game development as the game industry is in a remarkable state of change. With the advent of increasingly powerful smartphones and tablets as well as the ever-growing application stores for desktop computers and mobile platforms serving millions of users a day, it has never been easier for Independent Game Developers (also known as Indies) to enter the market with virtually no risks and very low budgets.

In this chapter you will learn about what Libgdx is and what the advantages are to use it for developing your own games. You will also get a brief overview of the feature set that Libgdx provides.

Before you can start developing games with Libgdx, you have to install and set up your development environment accordingly. You will be using the freely available and open source software Eclipse as your Integrated Development Environment (IDE ) and set up a basic project that uses Libgdx. It will feature a runnable example application for each currently supported target platform. These platforms are as follows:

Windows

Linux

Mac OS X

Android (Version 1.5 and above)

HTML5 (Using JavaScript and WebGL)

Note

The target platforms Windows, Linux, and Mac OS X will from now on be referred to as Desktop and also share a project in our development environment.

An alert reader may have noticed that iOS is missing in the list of supported target platforms. Fortunately, it is very likely that Libgdx will support the iOS platform soon as the developers have already put great effort into this feature. At the time of writing of this book, it is said that iOS, starting from Version 5.0 and above, will be supported.

Furthermore, you are going to explore what a game needs by looking at it from a technical standpoint, and why it is so important to plan a game project before the development starts.

At the end of this chapter, you will be introduced to the game project that is going to be developed and enhanced throughout this book.

Diving into Libgdx

Libgdx is an open source, cross-platform development framework, which is designed mainly, but not exclusively,