Getting Started in Android Game Development

If you're interested in developing a game for the Android platform, there is a lot you need to know.  I'm the developer of Light Racer, Light Racer 3D, Antigen, Deadly Chambers and Wixel, which are currently available on the Android Market. I've also been involved with the development of about 5 other games for Android and iOS and am co-author of Beginning Android Games 2nd Edition.  I've developed games before but the original Light Racer was my first Android application and I learned quite a bit about writing Android games that I'd like to share with everyone.  I even wrote an online book detailing the development of Light Racer 3D, which is full of how-tos and useful code snippets. If you have previous experience with game development, moving over to the mobile platform won't be all that difficult.  You will mostly just need to learn the architecture and API.  If you're new to game development, I have assembled a list of must-knows for getting started.  They apply to many different types of games, including action, strategy, simulation and puzzle.

Android is a Java-based environment.  This is nice for new developers as Java is widely accepted as a much easier language to get started in than C++, which is the norm for mobile development and is what I use now.  Google has also done an excellent job with documenting the API and providing examples to use.  There is an example to show functionality for almost 100% of the API, called API Demos.  If you're familiar with Java and have already used Eclipse, getting your first app working should be fairly simple.  If you've never coded anything in your life before, you will have a lot to absorb as you move forward, but don't get discouraged. If you have some experience and are wanting to develop a cross-platform game or high-performance Android game in C++, check out BatteryTech, which is a platform I wrote and am currently using for game development.

Get the SDK

The first step in getting started with the Android platform is to get the Android SDK (Software Development Kit).  The SDK has the core libraries, an emulator, tools and sample code.  I highly recommend using Eclipse and the android eclipse plugin.  Eclipse IDE for Java Developers is fine if you are just doing Android.  If this is your first Java development project, you will want to download the full Java SE Development Kit (JDK) as it contains tools you will need for signing and deploying your application.

Learn the application architecture

As tempting as it may seem to just dive right in, it's very important to understand the android application architecture.  If you don't learn it, you may design things in such a way that will make it very difficult to fix problems with your game down the line.  You will want to understand Applications, Activities, Intents and how they are all related to each other.  Google has provided good information on the architecture here.  The really important thing is to understand why your game may need to consist of more than one Activity and what that means to designing a game with good user experience.  This is where things tie in to the Activity lifecycle.

Learn the activity lifecycle

The activity lifecycle is managed by the Android OS.  Your activity will be created, resumed, paused and destroyed as the OS dictates.  Handling these events correctly is very important to having an application that behaves well and does what the user perceives as correct.  It's very good to know how all of this works before you start designing your game because you will save yourself debugging time and costly redesign time later on.  For most applications, the default settings will work but for games, you may want to consider turning the SingleInstance flag on.  When set as default, android will create new instances of the activity as it sees fit.  For a game, you may only want to have 1 instance of the game activity.  This has some implications for how you need to manage the state of things but for me it solved some resource management issues and it should be considered.

The main loop

Depending on what type of game you are writing, you may or may not have a main loop.  If your game is not time-dependent or if it only responds to what the user does and will wait forever for user input without making any kind of visual changes, you may not need a main loop.  If you are writing an action game or a game that has animations, timers or any kind of automation, you should seriously consider using a main loop.

The main loop of a game is the part that "ticks" sub systems in a specific order and usually as many times per second as possible.  Your main loop will need to run on its own thread.  The reason for this is that Android has a main UI thread and if you don't run your own thread, the UI thread will be blocked by your game which will cause the Android OS to not be able to handle any of its normal update tasks. The order of execution is usually as follows:  State, Input, AI, Physics, Animation, Sound and Video. 

Updating State means to manage state transitions, such as a game over, character select or next level.  Often times you will want to wait a few seconds on a state and the State management is the part that should handle this delay and setting the next state after the time has passed.

Input is any key, scroll or touch from the user.  It's important to handle this before processing Physics because often times input will affect the physics so processing input first will make the game more responsive.  In Android, the input events come in from the main UI thread and so you must code to buffer the input so that your main loop can pick it up when the time comes.  This is not a difficult task.  Defining a field for the next user input and having the onKeyPressed or onTouchEvent set the next user action into that field is all that will be required.  All the Input update needs to do at that point is determine if it is valid input given the state of the game and let the Physics side handle responding to it. 

The AI update is analagous to a user deciding what they are going to "press" next.  Learning how to write AI is out of the scope of this article but the general idea is that the AI will press buttons just like the user does.  This will also be picked up and responded to by the Physics update.

The Physics update may or may not be actual physics.  For action games, the point of it is to take into account the last time it was updated, the current time it is being updated at, the user input and the AI input and determine where everything needs to be and whether any collisions have occured.  For a game where you visually grab pieces and slide them around, it will be the part that is sliding the piece or letting it drop into place.  For a trivia game, it would be the part deciding if the answer is right or wrong.  You may name yours something else, but every game has a part that is the red meat of the game engine and for this article, I'm referring to it as Physics.

Animations aren't as simple as just putting an animated gif into your game.  You will need to have the game draw each frame at the right time.  It's not as difficult as it sounds.  Keeping state fields like isDancing, danceFrame and lastDanceFrameTime allows for the Animation update to determine if its time to switch to the next frame.  That's all the animation update really does.  Actually displaying the change of animation is handled by the video update.
 
The Sound update handles triggering sounds, stopping sounds, changing volumes and changing the pitch of sounds.  Normally when writing a game, the sound update would actually produce a stream of bytes to be delivered to the sound buffer but Android manages its own sounds so your options for games are to use SoundPool or MediaPlayer.  They are both a little sensitive but know that because of some low level implementation details, small, low bitrate OGGs will yield the best performance results and the best stability.

The Video update takes into account the state of the game, the positions of players, scores, statuses, etc and draws everything to screen.  If using a main loop, you will want to use the SurfaceView and do a "push" draw.  With other views, the view itself will call the draw operation and the main loop won't have to do it.  SurfaceView gives the highest frames per second and is the most appropriate for games with animation or moving parts on screen.  All the video update should do is take the state of the game and draw it for this instance in time.  Any other automation is better handled by a different update task.

What's this code look like?  Here's an example.

public void run() {
    while (isRunning) {
        while (isPaused && isRunning) {
            sleep(100);
        }
        update();
    }
}

private void update() {
    updateState();
    updateInput();
    updateAI();
    updatePhysics();
    updateAnimations();
    updateSound();
    updateVideo();
}


3D or 2D?

Before you start on your game, you need to decide if you're going to go 3D or 2D.  2D games have a much lower learning curve and generally are easier to get good performance on.  3D games require much more in-depth math skills and may have performance issues if you are not very careful.  They also require the ability to use modeling tools like 3D Studio and Maya if you intend to have shapes more complex than Boxes and Circles.  Android supports OpenGL for 3D programming and there are many good tutorials on OpenGL that one can find to learn it.

Build simple, high quality methods

When getting started, make sure that you avoid writing one big long monolithic method that is "the game."  If you follow the main loop pattern that I described above, this should be fairly easy.  Each method you write should accomplish one very specific task and it should do so error-free.  For example, if you need to shuffle a deck of cards, you should have a method called "shuffleCards" and that should be all it does. 

This is a coding practice that applies to all software development but it's particularly important in game development.  Debugging can get very difficult in a stateful, real-time system.  Keep your methods small and the general rule of thumb is that each method should have 1 and only 1 purpose.  If you're going to programatically draw a background for a scene, you may want a method called "drawBackground."  Things like that will make it so that you develop your game in terms of building blocks and you will continue to be able to add what you need without making it too complex to understand.
 
It's all about efficiency!

Performance is a major issue for any game.  The goal is to make the game as responsive as possible and to also look as smooth as possible.  Certain methods like Canvas.drawLine are going to be slow.  Also drawing an entire screen-sized bitmap onto the main canvas every frame will also be costly.  Balancing things like that is necessary to achieve the best performance.  Make sure to manage your resources well and use tricks to use the least amount of CPU to achieve your task.  Even the best game will not be very fun if it can't perform well.  People in general have little tolerance for choppiness or poor response.

Tips and Tricks

Take a look at the example for LunarLander in the SDK.  It uses a SurfaceView and that would be the appropriate view to use for a game that needs the highest number of frames per second possible.  If you're going 3D, take a look at GLSurfaceView. It takes care of the OpenGL device initialization and provides a mechanism for rendering.  For LightRacer, I had to optimize the way I have everything drawn or else the framerate would be drastically lower.  I drew the background to a Bitmap only once which was when the view is initialized.  The light trails are in their own bitmap which gets updated as the racers move.  Those two bitmaps are drawn to the main canvas every frame with the racers drawn on top and then finally an explosion.  This technique made the game run at a playable rate.

It's also a good practice to have your bitmaps be the exact size you intend to draw them on screen, if applicable.  This makes it so that no scaling is needed and will save some CPU.

Use a consistent Bitmap Configuration (like RGBA8888) throughout the game.  This will save the graphics library CPU in having to translate the different formats.

If you're determined to develop a 3D game but have no 3D knowledge, you will want to pick up a book or two on 3D game programming and study up on linear algebra.  At a bare minimum, you must understand dot products, cross products, vectors, unit vectors, normals, matrixes and translation.  The best book I have come across for this math is called Mathematics for 3D Game Programming and Computer Graphics.

Keep the sound small and at a low bitrate.  The less there is to load, the faster loading times will be and the less memory the game will use.

Use OGGs for sound, PNGs for graphics.

Make sure to release all media players and null out all of your resources when the activity is destroyed.  This will ensure that the garbage collector gets to everything and that you don't have any memory leaks between launches of the game.

Join the Android Google group and find community support.  There will be people that can help you along the way.

Above all, spend time testing and retesting and making sure that every little thing works exactly the way you would expect it to.  Polishing the game up is the longest and hardest part of development.  If you rush it out to market, you will probably have a disappointed crowd and you may feel that all your hard work is wasted.  It's not possible to have 100% of people love what you write but you should at least try to put out the highest quality work that you can.

Google has excellent documentation for getting started here.

Find working game code samples and how-tos in the Light Racer 3D Development Journal

Need a book recommendation? Try Beginning Android Games 2nd Edition by Mario Zechner and Myself (Author of libgdx and friend of mine).

Finally, Battery Powered Games offers pro Android (and iOS) game development consulting services so if your company has a need to contract out mobile game development, that's the place to go!

160 Comments

Post a comment here or discuss this and other topics in the forums

As Robert said, try to do

As Robert said, try to do everything slowly. Read his article for few times slowly analyzing the content. Find more articles on the internet, try to do something and you will definitely succeed. I am a mobile developer by myself, and sometimes there are some newbies coming to our company in order to learn something. It is hard to learn them do android, windows mobile or iphone applications from nothing. But they are learning slowly, trying to do something, asking me about their problems, and after some time they can do such apps for themselves.
What about this article, thanks a lot Robert. I will definitely use it as a methodical thing for teaching some newbies in my company. It is well written and understandable. I will be waiting for another great articles from you in the nearest future.

Sincerely,

Kevin Gickson

As far as I know, there's

As far as I know, there's mine (Light Racer Elite / 3D) and Chickenbrick's (Project INF). I don't think there is an abstract multiplayer engine because the netcode always depends on the world model and overall architecture so it's tough to just make a package that would actually work for most games. I recommend getting your game working then thinking about what design changes will be needed to add input and output pipelines.

Here's a good link - http://developer.valvesoftware.com/wiki/Source_Multiplayer_Networking

Those guys did a good job. If you can use constant rate snapshots and a pipeline, you'll have a great multiplayer engine.

I shall do that for sure. Our

I shall do that for sure. Our aim is actually to make a 2D multiplayer game for Android phones. Are there any multiplayer game engines that already exist for Android?

Hi Mehjabeen. Building a

Hi Mehjabeen. Building a game engine for Android is not much different than building one for other platforms with the exception of Dalvik VM optimizations. I recommend picking up some books on game engine development. They'll have everything you need.

Start slow. Get a few things to work. Understand them then refactor to make room for more. ALWAYS watch your performance. It's a major issue with mobile game development.

Good luck!

Game Engine

Hey..

I am new to Android Game Development. I read your article about programming the multiplayer engine for your games but did not understand much. Could you please tell me where I can learn how to build a game engine from scratch for Android phones or could you please tell me yourself? I'd really appreciate it. Thank you.

Some additional notes on performance

Hi Guys,

I'm woking on a game engine for Android and have also been coming across some performance stuff.
I wanted to outline a few no-go habits here. The most sensitive resources on the android is maybe the float calculations (no hardware float support) and the dalvik VM garbage collector. If you don't want to develop your own floating point libs, you can't really get around the float problem and I won't go into details here regarding floating point libs.

Regarding the GC I have a few tips for you:
* The golden rule is to avoid short term object allocation. All objects that are only used to do calculations should be better used in static fashion
* Try to avoid any strings in your code as they will mostly result in short lifetime objects. (yes, also debug messages will increase the object count dramatically, and specially in a game loop). You can fork the construction of the debug messages into a scope where you check for a global debug flag or something.
* When you use strings as id/references declare them somewhere as static finals.
* Don't use Set's. Try to use Lists (ArrayList, Vector).
* Start the standalone DDB console of the android toolkit and launch the Allocation Tracker feature in otder to see who / where / when you instance what objects and in what count. Check the reference to the code points and try to avoid any object creation if not absolutely needed. (i.e. instead of instancing a new ArrayList when you have a class that collects something and you need a fresh ArrayList just call ArrayList.clear())
* In a 30 fps game loop each object that gets instanced can be a show stopper. You need to minimize the count of instanced objects specially for objects which have a short lifetime anyway.
* NEVER use iterators (List.iterator() / for(Object o : objectList) ) they are causing lot of objets to be isntanced. Use the standard approach for(int i = 0; i < objectList.size(); i++)
* NEVER call a mehtode twice where potential calculations / allocations are involved . Create a local veriable and store the result with one singe call. i.e ArrayList.toArray() will allocate new memory for a copy of the internal elements and return a copy of the internal array. Avoid calling such a method twice and just store it localy.
* Try to use caches where possible.
* Also very important is that you understand Autoboxing and take into account the negative performance impact when using autoboxing. Every time a primitive type needs to be boxed into a complex type it will cause an other possible short lifetime object to be allocated. Generally the best thing to do is to use primitive data types where possible.

Have a nice day all of you :o)
Think geek, be smart!

Regards
Gion

Thanks for the tip

Thanks! I went back through and changed my background PNG to a jpeg @ 70% compression and that seemd to give me a little boost. Also, I read this android guide on "designing for performance" that I think was extremely helpful -- I think you should add it to your article in the part where you talk about game performance: http://developer.android.com/guide/practices/design/performance.html

Thanks again!

PNG is the right format for

PNG is the right format for files with transparency, otherwise JPG or GIF will work just fine. RGB 565 is an internal format. It only uses 16 bits and is the native format for the surface. It's small and fast, basically.

RGB 565?

hmm, I guess I'm not too familiar with "RGB 565". Is that a different image format? I'm currently just using .PNG images for my background and sprites. Is that not good?

Dynamic Backgrounds

Light Racer has a dynamic background. The trails themselves are part of it. It's very expensive to redraw all of the trails if there are many segments so I have it only drawing the little bit of trail that is changing to the dynamic background. The dynamic background itself is drawn to the main canvas every frame, then the racers, map objects, items, NPC and explosions.

When a trail is dropped, there is an animation that requires a full dynamic background redraw. I have a clean background (no trails) image that I first draw to it, then the current state of all trails. Then the regular drawing occurs with the racers, map objects, etc.

Does that make more sense?

If your game does not have a background that changes during gameplay, you don't need to worry about this. Just draw it every frame with RGB_565.

Optimizing Canvas drawing?

Thanks for the great article, it certainly helped me get my feet wet. You mentioned that one thing you had to do to optimize your light racer game was to make it so that you only drew your game's background when needed. I'm having trouble understanding how this is possible -- right now I'm using the background to "clear" the canvas every frame in my doDraw() method, so that I can re-draw on each frame. I'd like to be able to optimize my game, but how exactly do you maintain the background image without having to render it every frame, and at the same time move a sprite from one position to another w/o "copying" it (causing the trailing effect)?

Thanks!

Thanks for the article, great pep-talk for us up-and-coming Android game developers!

Thanks I see that they have

Thanks

I see that they have made a QUAKE port on it.
so it must be possible to use every processing powers for it.

Great! I hope you have a

Great! I hope you have a good experience. Don't expect the Android platform to be a huge OpenGL performer. It can do a small number of polys but nothing like you're used to on a desktop. I'll be diving in to it in a month or so.

Cool

Nice introduction on developing apps on Android.

I'm going to download the Android SDK, the Java SE SDK and eclipse
I'm going to see what I can of game I can milk out.

As a C/C++ programmer who had worked years with opengl
this is the first time ever I'm really diving into Java and Opengl SE

cheers

Great article.

This is a very well written article.

Thank you for it.

Switched this to Forum

Cass,

I hope you don't mind but we're running out of room here so I moved the discussion to the forum. Here is where you can continue (you'll have to register but it's relatively painless).

Thanks!

GameResources and animation

Hi Robert,
Yes, the GameResources object appears to be a nice solution to simplify the handling of the various bits of data.

How do you load images on RGB_565 or any of the others?

My problem is that I am currently using the movements of the person with relatively large images at 320x480, with alpha. It works, but it needs improvement as each of these PNGs have around 20k.

What do you reckon? I was wanting to come up with at least 10 movements of 3 frames each. That'd give me around 600kb of PNGs. I need to show only head and torso, so I suppose it would be best to separate them?

Many thanks and have a great week over there!

Cass Surek

PS: I've fixed the XML preferences screen I had on the previous post. Yay! :)

Consider a resource manager

Instead of having your Person hold its resources, you could have all resources for the game managed by a single class. When you create the person, you pass it this resource manager. I call mine GameResources and it is just a collection of bitmaps, paints and fonts that all of my different game objects use. Each game object needs it to be able to draw itself so it is passed in to each on the constructor. I also have a release() method for every game object that nulls out the game resources reference just in case.

GameResources is created by the thread and is responsible for loading everything. It is also responsible for unloading/freeing everything with the release() method. What you can do is initialize it in your activity and hang on to it there. Pass it to the thread and have the activity take care of cleaning it up onDestroy().

How big are your PNGs?? I have about 100 frames of animation loaded at any given time and don't have any memory issues. They range from 15x30 to 60x60 to 30x120. If any don't need transparency, make sure to load them using RGB_565. It is way faster than ARGB_8888. ARGB_4444 uses less memory but is very slow to draw. I also keep a 320x480 clean background bitmap (RGB_565), a 320x480 dynamic background bitmap (RGB_565) and a 320x480 text layer (ARGB_8888). I'd like to get rid of my text layer because those full screen layer draws are really slow.

Thanks

Hi Robert, I had taken a similar approach to what you described before even reading the other post. :) Thanks! I have a class called Person which has an Update() method that evaulates various conditions and then draws itself based on the current movement of the character. The animation works fine, although I will have to find another way of keeping the various frames of the several movements at hand, but not loaded all the time. The whole collection of PNGs appears to be too big for the memory available (gave me errors already).
The glitch I am getting now is after I return from an XML preferences screen, I have to check the thread state, delete and recreate it, as it gets finalised when the main activity loses focus. I can recreate the thread, but it is rather annoying as it takes forever to load all resources again (they are loaded within the Person class).
Anyway, I am progressing thanks to your help! Sincerely grategul for all your attention. :)

Cheers

Cass Surek

You are on-track

I like to load all of the frames into a class I call GameResources. That way the object can animate itself by keeping track of time and displaying the appropriate gameResources.characterAnimationFrame[i].

Say for instance you have a player character. You might want to call the class Player. Player would have fields for its location and what its doing. It should also have other state fields for modifications to it, like if it is currently on fire or exploding or jumping, standing, running, etc. Player should manage its states based on the input it receives and the result of the physics updates. Player can also draw itself and depending on what state it's in and what frame of animation is now selected, the drawing code can pull the appropriate frame from the game resources and draw it. Does that make sense? That's how I handle things. I encapsulate all of the functionality of a logical part of the game into a class like that and make it responsible for dealing with drawing itself.

Also - I've been asked this before so I did put together an article on How to handle interpolated animations using a main loop which has the code you're probably looking for.

SensorManager and Drawables

Hi again, worked beautifully, but I have used the sensor on the main UI thread, passing on details to the game thread as per the other methods.

I got to animate things using various Drawables, one for each frame. In my case, I need the character to do a specific movement, so I've created an array of Drawables which get drawn as the animation progresses. Is that the best approach in your opinion? Is there a more streamlined technique to draw the frames? I will have at least 10 movements, which might take a considerable amount of memory! :)

Many thanks!

Cass

Yes!

That is exactly how I do it in Light Racer 1 and 2.

I haven't dealt with the sensor yet but I would first try creating an instance within the thread, just like your other resources and managers. I like to have an init() method that loads graphics and sounds and gets a hold of my managers. I usually then have a release() method that cleans up everything init() created. It makes it easy to avoid memory problems by sticking to that.

Read about the design changes for Light Racer 2 in the Light Racer 3D Development Journal for how I do things.

Thanks!

Further comments

Hi mate, thanks again for your prompt help. I've played your game and enjoyed it very much - well done. :)

My java is a little rusty, but I am trying to get some hints from you whilst studying the LunarLander app.

The approach you mentioned is illustrated on the following, right?

public boolean onKeyUp(int keyCode, KeyEvent msg) {
return thread.doKeyUp(keyCode, msg);
}

The ImageView llistens for the action and then passes it on to the thread.

On a similar note, if you were to need to listen for sensor variations, would you instantiate the sensormanager within the thread as it does not need to receive any input from any View?

Cheers again for you patience and help.

Cass Surek

Thanks! I'm glad you found

Thanks! I'm glad you found the article helpful.

I have the view listen for key events. The events are sent into the thread through a direct method call which must be synchronized with the surface holder. Check the Lunar Lander game for an example.

How about the input from the UI thread?

Thanks for the very informative article.

If you used a separate game thread, how did you go about getting the input info to thre thread since they are handled on the UI thread?

Cheers,

Cass

1.5 is out now for developers

I saw that Google posted that 1.5 is available now for developers but it looks like many developers are having issues with it. I think it'll be a great release once the bugs are worked out. My guess is that many people are simply doing something wrong, but I haven't tried it myself yet. I plan to finish Light Racer 2.0 on 1.1, then start testing against 1.5 before the release and do all of Light Racer 3D against 1.5.

Android future

The technology seems to be pretty promising. Given the simplicity on its part. Its true that android and iPhone have very bright future for different reasons though. It all depends on the marketing strategy adopted by one over another. Undoubtedly Apple & Google, both have proven track records of their working methodologies. Let’s keep our finger crossed till Apple 3.0 comes out and Android’s 1.5 and G2 rocks the market.

Excellent understanding.

Thank you for your written expression and giving us a chance to improve android's market with your experience as a developer.

I'm currently building my first app for the android G1 market.

I've encounter problems until I read your post.

other than that, I hope I can finish my app without any errors.

Other Books

I've had a few different books over the years that I have learned from but I believe the most valuable one as far as general game programming was Game Coding Complete. There are a few others that give you some low-level tips like how to write really fast pixel-handling code and such but none of that really matters when targeting Android.