Libgdx android backend

libGDX Android Backend

Reference for Android-specific launcher setup, manifest configuration, lifecycle mapping, file access, input handling, screen density, safe insets, and threading.

Launcher Setup

AndroidApplication extends Activity. Call initialize() in onCreate():

public class AndroidLauncher extends AndroidApplication {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        AndroidApplicationConfiguration config = new AndroidApplicationConfiguration();
        config.useAccelerometer = true;   // default true — set false to save battery
        config.useCompass = false;        // default true — set false to save battery
        config.useGyroscope = false;      // default false
        config.useImmersiveMode = true;   // hides nav/status bars — libGDX handles it fully
        config.numSamples = 2;            // MSAA anti-aliasing (0 = off)
        config.useWakelock = true;        // keeps screen on during gameplay
        config.useGL30 = false;           // set true for GL ES 3.0 (Gdx.gl30); null if false
        initialize(new MyGame(), config);
    }
}

Do NOT add manual immersive mode code (deprecated SYSTEM_UI_FLAG_* constants, onWindowFocusChanged(), visibility listeners). config.useImmersiveMode = true is sufficient — libGDX manages the system UI internally. Never show working SYSTEM_UI_FLAG code examples, even as a "what not to do" — users will copy them.

For Fragment-based hosting, use AndroidFragmentApplication instead of AndroidApplication. It extends Fragment and works with FragmentActivity.

AndroidManifest.xml

<activity
    android:name=".AndroidLauncher"
    android:configChanges="keyboard|keyboardHidden|orientation|screenSize"
    android:screenOrientation="landscape"
    android:exported="true">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

android:configChanges is critical. Without orientation|screenSize, Android destroys and recreates the Activity on rotation — a full dispose() → create() cycle with GL context loss. With it, libGDX handles rotation via resize().

Permissions

Permission	When needed
WRITE_EXTERNAL_STORAGE	Gdx.files.external() — also needs runtime permission on API 23+
INTERNET	Any networking (HttpURLConnection, WebSocket, etc.)
VIBRATE	Haptic feedback via Gdx.input.vibrate()
WAKE_LOCK	Added automatically when config.useWakelock = true

Runtime permissions (API 23+): libGDX has no cross-platform permission API. Request in the launcher:

// In AndroidLauncher (any class extending AndroidApplication works)
if (Build.VERSION.SDK_INT >= 23) {
    requestPermissions(new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_CODE);
}
// Result arrives in onRequestPermissionsResult() — check grantResults before using external()

Lifecycle Mapping

Android	libGDX	What happens
onCreate()	create()	App initialization
onResume()	resume()	App returns to foreground
onPause()	pause()	App goes to background
finish() / system kill	dispose()	App shutting down

Use libGDX's ApplicationListener callbacks (create/render/pause/resume/dispose), NOT Android Activity lifecycle methods directly. Override onCreate() only for the launcher's initialize() call.

The render loop stops entirely during pause on Android. Any work in render() — timers, heartbeats, network pings — ceases when the app is backgrounded. Use a background thread or Android service for work that must continue.

OpenGL Context Loss on Pause

On Android, the OpenGL context IS destroyed when the app is paused. This is not limited to older devices — it happens on ALL Android versions.

• Managed resources (Texture, SpriteBatch, ShaderProgram, BitmapFont, FrameBuffer loaded via libGDX APIs) are automatically reloaded by libGDX on resume. You do not need to manually reload them.
• Custom non-managed GL resources (raw GL handles created via Gdx.gl.glGenTexture(), Gdx.gl.glCreateProgram(), etc.) must be recreated manually — register an invalidation callback or recreate in resume().

// WRONG — unnecessary manual reloading
@Override
public void resume() {
    texture = new Texture("sprite.png");  // libGDX already reloaded it
}

// RIGHT — only recreate raw GL handles if you have any
@Override
public void resume() {
    if (customGLHandle != 0) {
        customGLHandle = createRawGLResource();  // only for non-managed resources
    }
}

Save critical game state in pause(), not dispose(). On Android, dispose() may not be called if the OS kills the backgrounded process.

File Access

FileType	Maps to	Permission needed
Gdx.files.internal("file")	Android assets/ folder	None (read-only, bundled with APK)
Gdx.files.local("file")	Context.getFilesDir() (app-internal storage)	None (private to app)
Gdx.files.external("file")	App-specific external storage (getExternalFilesDir())	WRITE_EXTERNAL_STORAGE + runtime permission on API 23+
Gdx.files.absolute("/path")	Literal filesystem path	Discouraged on Android — use local() or external()

// Save game — use local(), not external() (no permission needed)
FileHandle saveFile = Gdx.files.local("savegame.json");
saveFile.writeString(json, false);

// Load game
if (Gdx.files.local("savegame.json").exists()) {
    String json = Gdx.files.local("savegame.json").readString();
}

// Read bundled asset (from android/assets/)
String levelData = Gdx.files.internal("levels/level1.json").readString();

Do NOT use desktop-style paths like "./saves/game.sav" or System.getProperty("user.home") on Android. These don't map to accessible storage.

Input

Back Button

By default, the Android back button exits the Activity. To intercept it:

// In create() or show()
Gdx.input.setCatchKey(Input.Keys.BACK, true);

// In your InputProcessor.keyDown()
@Override
public boolean keyDown(int keycode) {
    if (keycode == Input.Keys.BACK) {
        // show pause menu, go to previous screen, etc.
        return true;
    }
    return false;
}

setCatchBackKey(boolean) is deprecated. Use setCatchKey(Input.Keys.BACK, true) instead.

Touch Input

Touch is the primary input on Android. Multi-touch uses the pointer index (0 = first finger, 1 = second, etc.):

// Polling
if (Gdx.input.isTouched(0)) {
    float x = Gdx.input.getX(0);
    float y = Gdx.input.getY(0);
}

Accelerometer / Gyroscope

Must be enabled in AndroidApplicationConfiguration (accelerometer is enabled by default):

float ax = Gdx.input.getAccelerometerX();  // tilt left/right
float ay = Gdx.input.getAccelerometerY();  // tilt forward/back
float az = Gdx.input.getAccelerometerZ();  // up/down (gravity)

On-Screen Keyboard

// Show/hide soft keyboard
Gdx.input.setOnscreenKeyboardVisible(true);

// Dialog-based text input (shows native Android dialog)
Gdx.input.getTextInput(new Input.TextInputListener() {
    @Override
    public void input(String text) { /* user entered text */ }
    @Override
    public void canceled() { /* user cancelled */ }
}, "Title", "default value", "hint");

Screen Density

Gdx.graphics.getWidth()/getHeight() returns the actual pixel resolution, which varies widely across Android devices. Use getDensity() to convert between density-independent units (dp) and pixels:

float density = Gdx.graphics.getDensity();
// 1.0 = mdpi (160 dpi), 1.5 = hdpi, 2.0 = xhdpi, 3.0 = xxhdpi, 4.0 = xxxhdpi
float pixelSize = 48 * density;  // 48dp → pixels

Safe Insets (Notch / Cutout)

libGDX provides safe inset values directly — no need for a custom platform interface or raw Android DisplayCutout API:

int top = Gdx.graphics.getSafeInsetTop();
int bottom = Gdx.graphics.getSafeInsetBottom();
int left = Gdx.graphics.getSafeInsetLeft();
int right = Gdx.graphics.getSafeInsetRight();

Available since libGDX 1.9.10+. Returns pixels. Use these to offset UI elements away from notches and rounded corners.

Threading

render() runs on the GL thread. All OpenGL calls must happen on this thread.

To run code on the GL thread from another thread (e.g., network callback, Android UI thread):

// From a network thread:
Gdx.app.postRunnable(new Runnable() {
    @Override
    public void run() {
        // Runs on the GL thread next frame — safe to create textures, update game state
        Pixmap pixmap = new Pixmap(downloadedBytes, 0, downloadedBytes.length);
        texture = new Texture(pixmap);
        pixmap.dispose();
    }
});

Never create or modify GL resources from a non-GL thread. This causes silent corruption or crashes.

Gradle / Android Studio

The android module has its own build.gradle with the Android plugin:

android {
    compileSdkVersion 34
    minSdkVersion 19        // libGDX minimum
    targetSdkVersion 34

    defaultConfig {
        applicationId "com.yourpackage.game"
    }
}

dependencies {
    implementation project(":core")
    implementation "com.badlogicgames.gdx:gdx-backend-android:$gdxVersion"
    natives "com.badlogicgames.gdx:gdx-platform:$gdxVersion:natives-armeabi-v7a"
    natives "com.badlogicgames.gdx:gdx-platform:$gdxVersion:natives-arm64-v8a"
    natives "com.badlogicgames.gdx:gdx-platform:$gdxVersion:natives-x86"
    natives "com.badlogicgames.gdx:gdx-platform:$gdxVersion:natives-x86_64"
}

Note: The exact dependency syntax depends on the project generator (gdx-liftoff vs older gdx-setup). The natives configuration above is from the standard template — newer generators may use different syntax.

Common Mistakes

1. Adding manual immersive mode code — config.useImmersiveMode = true is all you need. Don't add SYSTEM_UI_FLAG_* listeners or onWindowFocusChanged() overrides.
2. Thinking GL context loss is only on old devices — It happens on ALL Android versions when the app is paused. Managed resources are auto-reloaded; only raw GL handles need manual recreation.
3. Manually reloading managed textures in resume() — libGDX handles this. Creating new Texture objects in resume() leaks the originals.
4. Using Activity lifecycle methods instead of libGDX callbacks — Use create()/render()/pause()/resume()/dispose(), not onStart()/onResume()/onPause().
5. Missing configChanges in manifest — Without keyboard|keyboardHidden|orientation|screenSize, rotation destroys and recreates the Activity instead of calling resize().
6. Using Gdx.files.external() without permissions — Needs WRITE_EXTERNAL_STORAGE in manifest AND runtime permission request on API 23+. Prefer Gdx.files.local() for save data.
7. Using desktop-style file paths on Android — "./saves/", System.getProperty("user.home") don't work. Use Gdx.files.local() or Gdx.files.internal().
8. Creating GL resources off the GL thread — Network callbacks and Android UI callbacks are NOT on the GL thread. Use Gdx.app.postRunnable() to marshal work to the GL thread.
9. Using deprecated setCatchBackKey() — Use Gdx.input.setCatchKey(Input.Keys.BACK, true) instead.
10. Saving critical state only in dispose() — On Android, dispose() may not be called if the OS kills the process. Save in pause().
11. Building a custom platform interface for safe insets — libGDX has Gdx.graphics.getSafeInsetTop() etc. built in (since 1.9.10+). No need for DisplayCutout API directly.