Mobile Game Framework

Stuff You Should Know…

• Genres• Paper Prototyping• Mechanics• Theme/Backstory

• Don’t Code!

General Game API

• Window/scene management• Input• File I/O– Playback recording (event logging)– Audio

• Graphics• General game framework/loop (w/ timing)

Window Management

• Handle basic Android OS events– Create– Pause– Resume

Input

• Polling– Code asks, “what is the current state?”– Info lost between polling

• Event-based – Queue of events stored

• Touch down, drag/move, up• Key down, up

Input Polling

• isKeyPressed(keyCode)• isTouchDown(id)• getTouchX(id)• getTouchY(id)• getAccelX()• getAccelY()• getAccelZ()

Event-based Input

• getKeyEvents()– Returns List<KeyEvent>

• getTouchEvents()– Returns List<TouchEvent>

File I/O

• Manage Java InputStream and OutputStream instances

• Load/use assets (audio, graphics, etc.)• Save data (state, high score, settings)

Audio Assets

• Music– Ambient/background– Streamed (open stream and play)– Play, pause, stop, looping (bool), volume (float)

• Sound– Shorter– Typically event-driven– Load entirely in memory– Play

• Dispose when not needed

Graphics

• Handle typical APIs like color, pixel maps, compression, double buffering, and alpha compositing

• Load/store imgs• Framebuffer– Clear– DrawSprite– Primitives– Swap– Height/width

Game LoopInput input = new Input(); Graphics graphics = new Graphics(); Audio audio = new Audio(); Screen currentScreen = new MainMenu(); Float lastFrameTime = currentTime();

while (!userQuit() ) {    float deltaTime = currentTime() – lastFrameTime;    lastFrameTime = currentTime();    currentScreen.updateState(input, deltaTime);    currentScreen.present(graphics, audio, deltaTime); }

cleanupResources();

Frame Rate Management

vs

Java/ADK Specifics

XML and the Manifest

Best Practices

• Utilize latest SDKs but be compatible back to 1.5

• Install to SD whenever possible• Single main activity that handles all events– Debatable relative to general Android App dev

• Portrait or landscape (or both?)• Access SD• Obtain a wake lock (keep from sleeping)

Defining Multi-Resolution Assets

• Handle difference devices– ldpi=36x36– mdpi=48x48– hdpi=72x72– xhdpi=96x96

• /res/drawable/ic_launcher.png– Same as mdpi – For Android 1.5 compatibility

Core Android Activity Events

• Create– Set up window/UI

• Resume– (Re)start game loop

• Pause– Pause game loop– Check isFinishing• Save state

Test Your Understanding

• LogCat (debugging event list)– Utilize debugging view in Eclipse

• Define new class that extendsActivity– Override • onCreate• onResume• onPause

– Check isFinishing()

Handling Touch Events

• setOnTouchListener(this)• onTouch(view, event)– Handle types of touch events– switch(event.getAction())

• MotionEvent.ACTION_DOWN• MotionEvent.ACTION_UP• …

– event.getX()• Multitouch involves handling array of touch data

Handling Key Events

• setOnKeyListener(this)• onKey(view, keyCode, event)– Handle KeyEvent.ACTION_DOWN– Handle KeyEvent.ACTION_UP

Accelerometer Input

• Check if accelerometer present on device– getSensorList(Sensor.TYPE_ACCELEROMETER)

• Register activity as listener to accelerometer events– registerListener(this, accel, m.SENSOR_DELAY_GAME)

• onSensorChanged(event)– event.values[0] <- x– event.values[1] <- y– event.values[2] <- z

• Deal with orientation by axis swapping

Asset File I/O

• assets/ folder quite useful via AssetManagerAssetManager am = getAssets();InputStream is = am.open(filename);…is.close();

External/SD Access

• Use <uses-permissions> in manifest• Check if external storage exists– Environment.getExternalStorageState();

• Get directory root– Environment.getExternalStorageDirectory();

• Utilize standard Java file I/O APIs

• Beware: complete SD access to read/write!

Shared Preferences

• Stores key-value pairs

p = getPreferences(Context.MODE_PRIVATE);e = p.edit();e.putString(key, value);e.putInt(key, value);e.commit();

String s = p.getString(key, null);int i = p.getInt(key, 0);

Sound Effect AudioSetup…setVolumeControlStream(AudioManager.STREA_MUSIC);soundPool = new SoundPool(max, AudioManager.STREAM_MUSIC, 0);

Get file descriptor and id:d = assetManager.openFd(“soundEffect.ogg”);int id =soundPool.load(d, 1);

Then play…soundPool.play(id, left, right, 0, loop, playback);

Finally…soundPool.unload(id);

Streaming AudioMediaPlayer mp = new MediaPlayer();AssetFileDescriptor afd = am.openFd(“ambient.ogg”);mp.setDataSource(afd.getFileDescriptor(), afd.getStartOffset(), afd.getLength());mp.prepare();mp.start();…mp.setVolume(left, right);mp.pause();mp.stop();mp.setLooping(bool);

Handle when completed:mp.isPlaying()mp.setOnCompletionListener(listener);

mp.release();

Well-Lit GraphicsKeep screen completely on with wake lock…

• Setup– <uses-permission> in manifest

• onCreate– PowerManager pm =

(PowerManager)context.getSystemService(Context.POWER_SERVICE); – WakeLock wl = pm.newWakeLock(PowerManager.FULL_WAKE_LOCK, "My

Lock");• onResume

– wl.acquire();• onPause

– wl.release();

Full Screen Graphics• Remove the title bars• Get full resolution for graphics/display

• In onCreate:

requestWindowFeature(Window.FEATURE_NO_TITLE);

getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);

NOTE: do this before setting the content view of activity!

FPS++

• Heretofore, the application only refreshes/draws itself in response to events

• This is good given battery considerations• But we can increase the FPS/draw rate

• Inherit from View• Define onDraw(Canvas) method• Invoke ‘invalidate’ at the end of onDraw

• Don’t forget to set the content view to a new instance of this derived class

The Limitless Possibilities of Canvas

• Canvas (parameter to onDraw) provides a wealth of options– getWidth();– getHeight();– drawPoint(x,y,paint);– drawLine(x1,y1,x2,y2,paint);– drawRect(x1,y1,x2,y2,paint);– drawCircle(x,y,radius,paint);

• Paint– setARGB(a,r,g,b);– setColor(0xaarrggbb);

Drawing Bitmaps/Sprites

• Bitmap– InputStream is = assetManager.open(file);– Bitmap bmp = BitmapFactory.decodeStream(is);– getWidth();– getHeight();– When done, bmp.recycle();

• Drawing the Bitmap– canvas.drawBitmap(bmp, x, y, paint);– canvas.drawBitmap(bmp, srcRect, dstRect, paint);

Drawing Text

• Fonts are placed in the assets/ directory• Then loaded– Typeface font =

Typeface.createFromAsset(context.getAssets(), fontFileName);

• Set the paint instance– paint.setTypeFace(font);– paint.setTextSize(x);– paint.setTextAlign(Paint.Align.LEFT|CENTER|RIGHT);

• Draw using canvas– canvas.drawText(string, x, y, paint);

Problem with onDraw/invalidate

• This presumes nothing else in the game runs• UI dominates• View vs SurfaceView• We want to have a thread running to do rendering• Create new class that inherits SurfaceView

– Maintain thread– Implement run, pause methods

• To draw– Canvas c = holder.lockCanvas();– c.draw…– holder.unlockCanvasAndPost(c);

SurfaceView Subclass

Using SurfaceView Subclass