Learning Android Game Programming NOTES

Learning Android Game Programming NOTES:

People have been playing games on computers for almost as long as electronic computers
have existed, and a rich variety of games has been invented. In her book, Reality Is
Broken, Jane McGonigal says that most games have four attributes:

1) A goal: Games clearly define a goal for the players to achieve. It’s important that the
goals be challenging, yet achievable. Ideally, players are always playing at the leading
edge of their ability. Goals give the players a sense of purpose in playing the game.

2) Rules: Games have rules that all the players agree to follow. The rules often make
achievement of the goal difficult, which in turn encourages players to be creative.

3) Feedback: A game has to tell the players how they are doing. Indeed, an interesting,
creative feedback system is key to making a game enjoyable.

4) Voluntary participation: It just isn't a game unless you really want to play. This aspect
of games implies the players’ acceptance of the goal, rules, and feedback system.
Before we create a new game, we want to think about which types of games exist, as
well as which types work well on mobile devices and which don’t. We also want to
take a look at the components that are common to all computer games.

Game Genres
Game developers didn’t start out categorizing their games, and there is no standard list
of categories. Nevertheless, over time games have been grouped into classes by different
people in different ways. The categories identified in this section are not meant to be
canonical, and they admittedly overlap in a number of areas. The exact categorization
really isn’t important—the point is that numerous types of games can be developed.

Skill or Action Games
Action game players typically have to use some real-time skill (e.g., jump a barrel
at the right time, shoot at a moving target) to be successful. Subtypes with some
examples include the following:
- Maze games
- Platform games where the player moves platforms around either to get
somewhere
or to stop adversaries
- Tower defense games: the player defends something (the tower) from an
oncoming
horde of bad guys
- Shooters: with the playing field either fixed, sliding, or scrolling
- One-on-one fighting games: where two opponents battle it out
- One-to-many fighting games: where the player fights through a gang of
opponents
(often martial arts related)
- First-person shooters (FPS): where the player’s view is that of the shooter
- Third-person shooters: same as FPS, but the point of view is that of a third
person

Strategy Games
Strategy games are less about reacting to real-time events, and more about devising
and implementing a strategic plan to overcome obstacles. They include the following
types of games:
- Turn-based games: including traditional board games
- Timed strategy games: where each move occurs in a fixed time
- Massively multiplayer online role-playing games (MMORPs): an extension of
the old Dungeons and Dragons genre, in which players assume roles and play
against others online

Adventure or Storytelling Games
Adventure and storytelling games are built around a rich storyline, with well-developed
characters and a story that defines the player’s purpose in playing the
game.
- Simpler 2D story games often involve mazes and interactions with other game
entities.
- Complex 3D story games can show different points of view as the game is played
and the story spun. Some have been turned into Hollywood movies.

Simulation Games
Typically, simulation games depict some real situation, such as a vehicle that the player
can operate. The games reproduce the physics of the real situation and can be good
enough to use for instruction as well as for just playing a game. They include the following
types of games:
- Sports simulators
- Flight or space simulators
- Driving or racing simulators
- Boat or submarine simulators
- Life simulators (overlap with strategy games)

Puzzle Games
Many puzzle games are direct translations of printed puzzles (e.g., crosswords), but the
genre also includes matching and hidden object games. Complex games often include
smaller puzzle games to solve as part of the larger game. Examples of puzzle games
include those based on the following concepts:
- Word based (e.g., crosswords)
- Number/math based (e.g., Sudoku)
- Visual matching
- Hidden object (e.g., Minesweeper)
- Construction from a set of pieces

Augmented-Reality Games
It’s fine to play games just for the fun of it, but sometimes there’s a bigger motive. As
Jane McGonigal’s Reality Is Broken points out, some games are intended to augment
reality in such a way that our real lives are made easier. Examples of augmented-reality
games (ARGs) include the following games:
- Jetset: a game that simulates the security line at an airport (to help you pass the
time while you wait in the real line)
- Chore Wars: a game that turns household chores into creative competition
- World Without Oil: a game that encourages energy conservation by simulating a
world where oil products are in very short supply

Games for Mobile Phones
With this rich variety of game types to choose from, we need to focus on those
that are most appropriate for mobile platforms such as phones and tablets. We also
need to focus on those games whose development by a small group of people is
feasible.
Given the potential size of the mobile device games market, it’s not surprising that
a substantial amount of research and thought have been put into what makes a good
mobile game. The usual principles of good computer game design still apply, along
with special characteristics of good mobile games:
- Don’t waste the player’s time.
- Provide help on playing the game.
- Make the game goals easy to understand.
- Show game status clearly.
- Mobile users typically play games in short sessions.
- Players need to easily pause and resume a game, and the phone should be able to
pause and resume games when necessary (e.g., for an incoming call).
- Players should be able to make game progress in a short period of time.
- Mobile devices have physical constraints that affect games:
- Small screen size and a variety of screen sizes, resolutions, and pixel densities
- Variety of user input methods (e.g., one- and two-handed operation, touch,
keypad, multi-touch, keyboard, Dpad, trackball)
- Limited computational power
- Limited battery (a factor that limits power-intensive graphics and computing)

Even if you had the development resources to create a really snazzy 3D first-person
shooter game like Halo, players are unlikely to sit with their smartphone and play it
for hours the way they might with the XBox version. Users are much more likely to
play mobile games in short sessions, pausing and resuming the game perhaps days later.
Speaking of resources, what does it take to create a commercial game? A typical
console game for a single console can easily take $10 million to develop, and two or
three times that amount for multiple-console development (it has been estimated that
some complex games cost as much as $100 million to create). The software development
kit (SDK) and license to create a console game alone can cost thousands of dollars.
If you think about what goes into a professional 3D console game, it’s easy to see
where the costs mount up—3D artwork, motion capture, animation, game play, user
testing, and software development are all both time consuming and expensive.
This book is about you and maybe one or two friends creating your own mobile game
for the Android platform. The Android SDK is free, and as of this writing, it costs only
$25 to sign up for Android Market and sell your game to anyone with an Android device.
We’ll stick to 2D (two-dimensional) games, which makes the artwork and the programming
simpler. As you’ll see, the basic game structure and components of any 2D game are
pretty much the same no matter what the genre, but we need to pick one as an example.

Components of a Typical Game
Before we look at the specifics of the example game, let’s examine the general components
that we need to work into the game and implement in the code. Here are some
components that will be part of our game.

- Opening (Splash) Screen
To maximize performance as the game is being played, the graphics needed for a game
level are often loaded before the level is started. During the loading process, which can
take several seconds, you don’t want to leave the user with a blank screen, so you display
a splash screen. It lets the user know that the game is working as it should. Splash
screens are optional, but we’ll include one in our game, just to show how it’s done.

- Menu Screen
Once the game is ready to run, we’ll need a place for the user to enter various options
(e.g., turn the sound on/off, get help in playing the game). This is typically done with
a graphical menu screen that presents the options and either implements the option or
calls another screen (such as Help) to do so.

- Music
For most of us, music has strong emotional inf luence. Background music is very
important for setting the mood of your game, and helping with the transitions
between parts of the game.

- Sound Effects
Sound effects can make a game a lot more fun. When two objects collide, players
expect to hear a sound of some kind—whether it’s a clang, a thud, or a boing. Our
example game also incorporates sound effects for each of the game characters. Each
villain has a characteristic sound effect accompanying his or her presence in a scene.

- Time
Most games will incorporate time—either clock time (scoring completion of a puzzle
based on the time taken to solve the puzzle) or playing against moves the computer
(or computer-driven adversaries) makes in real time. In our game Virgins Versus
Vampires (V3), this factor takes the form of killing the villains before they can reach
the virgins.

- Lives
Games have to be challenging to be fun, so the player has to fail every once in a
while. Killing the player off (in a virtual way) is a convenient way to give failure a
consequence. Some games give the player multiple lives per session, whereas others
(and V3) give the player only one life.

- Obstacles
Obstacles are used in different ways in different games. In many games, the player is
trying to achieve some goal, and obstacles are thrown in the player’s path. In tower
defense games (and V3), it’s the adversaries who are trying to reach a goal, so the
player throws obstacles in their paths.

- Levels
Challenging games are fun, but it’s important to provide a range of challenges, so that
players can start with easy challenges and gradually ramp up to higher challenges as
their game-playing skills and experience improve. Levels are a proven way to achieve
this effect—the player learns how to play the game in the first few levels, and his or
her skills have to continue to improve as new levels are presented. This is also a great
way to add some variety to the game.

- Adversaries
The adversaries in a game are sometimes referred to as entities (although AndEngine
uses that word to mean something else). These characters are the villains (or other
players) that the player must overcome to win. They are distinct from obstacles in that
they take action against the player—obstacles are more passive. We’ve listed the entities
for V3 later in this chapter, along with an outline of their behavior.

 - Player
Of course, the player is the most important component of any game. The whole point
is to keep the player engaged and interested so he or she will keep playing the game.
The player has to be challenged by the game, but not too challenged to give up in
frustration. The game has to include enough variety to maintain the player’s interest,
and rewards have to be doled out to recognize success in playing the game.

- Scenes
If you think of the game as something like a movie, each screen that is displayed to the
player is something like a movie scene. Each scene has background graphics that don’t
change much (although the player’s point of view might change). Animated graphics
are then added to the scene to implement the entities and obstacles that interact to
make the game.

Once you have a game concept outlined, the next step in designing a game is to envision
the scenes needed and describe the f low among them. Screenwriters and many
creative writers do this by making a storyboard with pencil and paper, using an index
card or drawing a rectangle for each scene, and creating a very rough sketch of the
scene and a few words to describe what’s going on there. You can show the transitions
between scenes with an arrow and a brief description of when the transition
takes place.

AndEngine Game Concepts
The movie analogy we referred to earlier is a good way to approach AndEngine. Your
game is like a movie, and the game engine includes concepts that are analogous to
those involved in making a movie.

- Camera
The “camera” of the game determines the view of the game that is presented to players.
It is very much like a movie camera in two-dimensional space. The camera can
pan and zoom across the scene to change the view presented. The panning and zooming
can either be under the player’s control or be driven programmatically.

- Scene
A game, like a movie, consists of a series of scenes where the action takes place. In a
movie, the scenes are edited together in a fixed way. In games, the sequence of scenes
is driven by the play of the game. Games are like movies edited on the f ly.

- Layer
Scenes are composed of layers of graphics. The layers are superimposed on one another,
much like the animation cels used to create cartoons in the old days. Layers can also
be used to introduce 2½D effects, where, as the camera pans, closer layers move faster
than more distant layers.

- Sprite
Sprites are the visual representation of the actors in our movie, whether those actors
are people or objects. Sprites can be animated or not, but they often move about the
scene during the course of game play. Sprite textures are often loaded from one large
image that comprises a collection of sprite images, called a sprite sheet.

- Entity
In AndEngine, entities are just about anything that’s drawn to the screen. Sprites
are entities, as are tiles, geometric shapes, and lines drawn on the screen. All entities
have properties, such as color, rotation, scale and position, that can be changed by
modifiers.

- Modifier
Modifiers change the properties of an entity, and they are very powerful in
AndEngine.
They can be used on any entity, and the change they cause can either
be immediate or occur gradually over a specified duration. In our game, we’ll use
modifiers frequently to create effects with sprites and other entities.

- Texture
A texture is a 2D, generally bitmapped graphic that can be applied to objects to give
them, well, texture. Textures define the way entities look, and much of the OpenGL
graphics environment is built around the use of textures.
Texture Region
A texture defines a complete bitmap graphic, and a texture region defines a subset of
that region. We’ll talk a lot about performance optimizations of 2D graphics later, and
using texture regions to map small pieces of a large combined bitmap is one of the key
tricks used to create these optimizations.

- Engine
An engine runs a scene. It takes care of letting animations and modifiers know when to
update the presented graphics, coordinates the actual drawing, handles user input events
(touch, keys, sensors), and generally manages the progress of the game. The engine is a
lot like the producer/director of our movie, telling everyone what they need to do.
- BaseGameActivity
This class, which extends the Android Activity class, will be the basis of each scene
in our game. BaseGameActivity does all the work common to all scenes, setting up
the game engine, conforming to the Android Activity Lifecycle requirements, and
enabling sensors. We’ll explore this class in more depth in Chapter 3.

- Physics Connector
AndEngine includes basic physics capabilities in the base engine, but the Box2D physics
engine expands greatly on those capabilities. We connect AndEngine objects with
Box2D through a physics connector. If your game doesn’t use Box2D physics, you
won’t have a physics connector.

Box2D Physics Engine
AndEngine includes the open-source JBox2D port of the Box2D physics engine. It
can be used to realistically simulate the interaction of physical objects in the following
ways (among others):
- Simulation of the physics of rigid bodies
- Stable stacking
- Gravity
- User-defined units
- Efficient solving for collisions/contacts
- Sliding friction
- Boxes, circles, and polygons
- Several joint types: distance, revolute, prismatic, pulley, gear, mouse
- Sleeping (removes motionless bodies from simulation until touched)