Mobile Game Development on Android

100 Pages·2012·1.31 MB·English

by  Matthew R. Young

Mobile Game Development on Android

Matthew R. Young

Problem Report submitted to the
Benjamin M. Statler
College of Engineering and Mineral Resources
at West Virginia University
in partial fulfillment of requirements
for the degree of

Master of Science
in
Computer Science

Frances L. Van Scoy, Ph.D., Chair
James D. Mooney, Ph.D.
Arun A. Ross, Ph.D.
Lane Department of Computer Science and Electrical Engineering

Morgantown, West Virginia
2012

Keywords: Android, OpenGL, Java, Game Development
Copyright 2012 Matthew R. Young
ABSTRACT
Mobile Game Development on Android
Matthew R. Young

Mobile device popularity has flourished in the past two years and continues to gain
momentum. Devices utilizing multi-touch screens such as tablets and smartphones
have created a new environment that opens up many possibilities for gaming. The
purpose of this project is to explore computer graphics and gaming on mobile devices.
To effectively explore this area, an arcade shooter game, similar to Asteroids, was
created and the development process has been detailed to allow the reader to recreate
the game while learning about graphics programming on the Android platform.
iii

Acknowledgments
I would like to thank Dr. Van Scoy for being my committee chairperson and for her
guidance and feedback during this endeavor. I also want to thank Dr. Mooney and Dr.
Ross for being on my committee.
Lastly, I want to express my gratitude to the Lane Department of Computer Science and
Electrical Engineering for the financial assistance received during my graduate studies
by being awarded a graduate teaching assistantship for CS101 and for the invaluable
teaching experience gained.
iv

Table of Contents
Acknowledgments........................................................................................................ iii
Table of Contents ......................................................................................................... iv
1. Introduction ............................................................................................................... 1
2. Mobile Devices .......................................................................................................... 2
3. Matrix Primer ............................................................................................................. 3
3.1 World Space and Transformations ......................................................................... 4
3.1.1 Translation ....................................................................................................... 4
3.1.2 Scaling ............................................................................................................. 4
3.1.3 Rotation ........................................................................................................... 5
3.1.4 Other Transformations ..................................................................................... 5
3.2 Eye Space and the View Matrix ............................................................................. 6
3.3 Screen Space and the Projection Matrix ................................................................ 6
3.3.1 Orthographic Projection Matrix ........................................................................ 6
3.3.2 Perspective Projection Matrix .......................................................................... 7
3.4 Putting it all together .............................................................................................. 8
4. OpenGL ...................................................................................................................... 8
4.1 OpenGL Shading Language (GLSL) .................................................................... 10
4.1.1 Uses of Shaders ............................................................................................ 10
4.1.2 GLSL Data Types .......................................................................................... 11
4.1.3 Vertex Shaders .............................................................................................. 11
4.1.4 Fragment Shaders ......................................................................................... 11
4.1.5 Shader Example ............................................................................................ 12
4.2 OpenGL ES 2.0 .................................................................................................... 12
5. Gaming Environments ............................................................................................ 13
6. Developing Demise ................................................................................................. 14
7. Game Components ................................................................................................. 15
7.1 User Input ............................................................................................................ 15
7.2 Overview of Game Classes .................................................................................. 15
7.2.1 GameManager Class ..................................................................................... 16
7.2.2 Level Class .................................................................................................... 16
7.2.3 MovingObjects Class ..................................................................................... 17
7.2.4 Player Class .................................................................................................. 17
7.2.5 HUD Class ..................................................................................................... 17
8. Demise: A Tutorial ................................................................................................... 18
8.1 Creating the Renderer .......................................................................................... 18
8.2 Creating the GLHelper Class ............................................................................... 20
8.3 Vector3d Class ..................................................................................................... 21
8.4 Drawing Objects ................................................................................................... 21
8.5 Background .......................................................................................................... 23
8.6 Model Class ......................................................................................................... 27
8.7 Joystick Movement ............................................................................................... 28
8.8 MovingObject Classes ......................................................................................... 30
8.8.1 PlayerObject Classes .................................................................................... 32
8.8.2 EnemyObject Classes ................................................................................... 32
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8.9 Explosion ............................................................................................................. 33
8.10 Game Levels ...................................................................................................... 34
8.11 GameManager ................................................................................................... 35
8.12 Player Class ....................................................................................................... 35
8.13 Heads-up Display ............................................................................................... 37
8.14 SoundManager................................................................................................... 38
9. Future Work / Expansion ........................................................................................ 39
10. Challenges ............................................................................................................. 40
11. References ............................................................................................................. 41
Appendix A: Source Code .......................................................................................... 42
Background.java ........................................................................................................ 42
Enemy1.java .............................................................................................................. 45
Enemy2.java .............................................................................................................. 46
Enemy3.java .............................................................................................................. 48
EnemyObject.java ...................................................................................................... 49
EnemyShip.java ......................................................................................................... 49
Explosion.java ............................................................................................................ 49
GameActivity.java ...................................................................................................... 52
GameManager.java.................................................................................................... 53
GameOverActivity.java ............................................................................................... 54
GLESRenderer.java ................................................................................................... 55
GLESSurfaceView.java .............................................................................................. 56
GLHelper.java ............................................................................................................ 56
HUD.java .................................................................................................................... 60
Joystick.java ............................................................................................................... 66
JoystickListener.java .................................................................................................. 69
Level.java ................................................................................................................... 70
Level1.java ................................................................................................................. 74
MainMenuActivity.java ............................................................................................... 75
Model.java .................................................................................................................. 76
MovingObject.java ..................................................................................................... 80
Player.java ................................................................................................................. 86
PlayerBullet.java ........................................................................................................ 90
PlayerObject.java ....................................................................................................... 90
PlayerShip.java .......................................................................................................... 90
PlayerShip1.java ........................................................................................................ 92
SoundManager.java ................................................................................................... 93
TutorialActivity.java .................................................................................................... 94
Vector3d.java ............................................................................................................. 94
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1. Introduction
The purpose of this project is to better understand computer graphics on mobile
devices. Computer graphics have been a strong interest of mine in the past several
years which led to choosing this area of study. One of the most effective ways to
demonstrate graphics concepts is to create an interactive video game. Due to a strong
personal interest in game development, this medium was chosen for the project.
Developing a game involves the same software engineering principles as a traditional
computer program. However, instead of displaying text to the user as output, graphics
are rendered and presented to the user.
The paper is divided into two major sections. The first consists of background
information in computer graphics to establish some understanding of the concepts used
in the project. The second portion consists of an explanation of the game Demise
created for this project. The game structure is discussed as well as a guide on creating
the game from scratch.
Demise is homage to retro 2D arcade shooters such as Asteroids and similar to modern
games such as Geometry Wars and Waves. The player controls a ship and is allowed
to move around the map and can fire in any direction while defending against a never
ending onslaught of enemies. The goals of the game are simple—survive the longest
and achieve the highest score.
Many of the prominent computer graphics concepts are implemented in Demise. The
game objects are three dimensional models so the game must implement a model
loader in order to load the attributes such as vertex and normal information from
external files. Textures are used heavily in order to create a visually appealing, multiple
layer background where the gameplay takes place. To provide graphical effects
shaders are implemented that allow model information to be modified at runtime by the
GPU.
The intended goal of this project is to provide some base understanding to those
interested in mobile game development and to provide an example game as a guide.
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There are many features that can be implemented that are currently not included in the
finished product and the reader is invited to use this project as a building block for future
development.
2. Mobile Devices
Mobile devices are becoming increasingly prevalent in today’s society after the rising
popularity of smartphones such as the iPhone, Android, and Windows based phones.
Due to the success of the mobile operating systems and the multi-touch capable
screens, tablet devices are also becoming very popular by providing a much larger
screen and offering the same functionality as their smaller phone counterpart.
The multi-touch screens of modern mobile devices have created an environment that
allows for effective human-computer interaction without the need for physical input
devices such as a mouse and keyboard. The mouse has been replaced by the ability to
press the screen to click and the keyboard has been replaced with an onscreen
keyboard. This allows for a more compact mobile device, and many of the current
devices are more than capable of performing many everyday personal computing needs
such as email, web, document processing, and even software development.
As with any new technology, the gaming industry always finds a way to utilize it to
create new and innovative ways to develop and play games. Gaming on cell phones
have been popular since the 1990s and with the power and capability of current mobile
devices, it is no surprise that gaming has been tremendously successful. The multi-
touch screens allow for direct interaction with the screen and can be used to move
avatars around a computer generated world or play a game of Scrabble by dragging
letters across the board just like the physical game. There is an endless possibility for
games to utilize the technology in mobile devices.
According to a study conducted by ABI Research, it is estimated that the revenue
generated from mobile gaming was $5 billion in 2011 and is estimated to increase to
$16 billion by 2016 [6]. This revenue potential can be very appealing to independent
developers who are looking for a platform that allows for self-publishing and for which
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the only development cost is the initial development license and a portion of revenue
earned.
Most successful mobile games can be classified as casual games. Casual games often
refer to those that do not require large time commitments and have a low learning
curve. The appeal of casual games is the ability to play them for a few minutes at a
time while still providing entertainment in that short window of free time.
There are many platform choices for developers including Apple iOS, Android, and
Windows phone. Most successful mobile applications utilize technologies that allow for
high portability across platforms for maximum success.
Android was chosen as the platform for this project for a few reasons. The leading
factor is that Android devices control 48.6% of the smartphone market share followed by
Apple iOS at 29.5% [4]. The popularity of Android devices can be contributed to the fact
that multiple phone and tablet manufacturers, such as Samsung, Motorola, and LG, are
utilizing the Android operating system whereas iOS is an Apple-only operating system
on the iPhone and iPad. Two other contributing factors for choosing Android were the
availability of a current Android device and the ease of use of the Android SDK.
3. Matrix Primer
A crucial element of graphics programming is the ability to utilize and manipulate
matrices to achieve a desired transformation. Typical transformations include
translation, rotation, and scaling. Within each of these transformations, a function exists
that takes a point and maps it to another point [1].
Matrices are not only used for applying transformations to objects of a scene but are
essential to converting a three dimensional world space to a two dimensional screen.
This is referred to as the projection matrix and is discussed further in this section.
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3.1 World Space and Transformations
To begin, an object contains a list of vertices, known as a vertex array. This is often
referred to by model coordinates and is located in what is called object space. These
are simply the coordinates before being placed into the scene.
World space refers to objects whose local coordinates are within the scene. Within
world space several transformations can be applied to manipulate an object’s vertices to
produce desired effects. These transformations change the size of the object, its
position in the world, or both.
3.1.1 Translation
A translation displaces a homogeneous point P = (X, Y, Z, 1) by a factor of D = (αX, αY,
αZ, 1). The new location, P’, is the result of the displacement. For example, if we
wanted to move the point (1, 1, 10, 1) five units in the X direction and three units in the
Y direction, our displacement vector would be (5, 3, 0, 1) which would give us a new
point of (6, 4, 10, 1). In Figure 3.1, we can see how we can use matrices to achieve this
transformation.

( ) ( ) ( )( )

Figure 3.1 - Translation Matrix [1]
3.1.2 Scaling
A scaling transformation simply increases or decreases the point by a specified factor.
This transformation is performed based on an origin point which can either be the true
origin or one that has been translated previously. Scaling can be performed in one or
all axis directions. If we wanted to transform a sphere to be an ellipsoid shape we could
multiple the X and Z coordinates by a factor of 0.5 which would result in the height of
the shape being twice the length of the width and depth. The scaling matrix is shown in
Figure 3.2.
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( ) ( ) ( )( )

Figure 3.2 - Scaling Matrix [1]
3.1.3 Rotation
The last key transformation is rotation. With this transformation, a given point is rotated
about an origin (world or translated) by a given angle. For example we may have a
point (4, 5, 9) and we want to rotate this point 45 degrees around the Y axis and 30
degrees around the Z axis. This transformation requires a little more calculation
compared to translation and scaling because it must be performed for each axis
rotation. It is also very important to note that the order of the rotations determine the
final result of the transformation (e.g. rotating 90 degrees around the X axis then
rotating 90 degrees around the Y axis produces a different result in reverse). The three
rotation transformations are provided in Figure 3.3.

( ) ( )( )

( ) ( )( )

( ) ( )( )

Figure 3.3 - Rotation Matrices [1]
3.1.4 Other Transformations
Translation, scaling, and rotation are the most common transformations used in
graphics. However, these are not the only basic transformations that exist. Others
include shearing and reflection. Additional transformations can be achieved by
combining these basic types of transformations [1].