meta-quest/hz-android-2d-porting

Android 2D App Porting to Horizon OS

When to Use

Use this skill when:

• Porting an existing Android 2D app to run on Meta Quest headsets
• Adapting a mobile Android app for Horizon OS panels
• Troubleshooting input, layout, or compatibility issues with a 2D app on Quest
• Preparing an Android app for Horizon Store submission
• Evaluating whether an existing Android app is compatible with Horizon OS

Overview

Horizon OS is built on Android (AOSP) and can run standard Android applications inside panels -- floating 2D windows positioned in 3D space. Most well-built Android apps work on Quest with minimal changes, but several areas require attention:

1. Input: There is no touchscreen. Users interact via controller pointer (ray-casting), hand tracking, or connected peripherals.
2. Layout: Apps run in resizable panels, not full-screen on a fixed display.
3. Design: Apps must meet Horizon OS design requirements for Horizon Store approval.
4. Performance: Quest uses a mobile GPU (Adreno) with thermal constraints.

The goal of porting is to make the app feel native to the Quest experience while preserving existing functionality.

Porting Workflow

Step 1: Initial Testing

Invoke hzdb (the Quest device CLI) via npx -y @meta-quest/hzdb <args> — no global install needed; npx fetches the latest published version on demand.

If using npx, use npx -y @meta-quest/hzdb as an alternative to calling hzdb found in this doc.

Install the existing APK on a connected Quest device and test basic functionality:

hzdb app install path/to/your-app.apk
hzdb app launch com.example.yourapp

Note any immediate issues: crashes, black screens, input problems, or layout breakage.

Step 2: Input Adaptation

The most common porting issue is input. Touch events are translated from the controller pointer, but:

• Hover states are now visible (users point before clicking)
• Scrolling uses the thumbstick, not swipe gestures
• Multi-touch gestures (pinch-to-zoom) do not translate directly
• Tap targets must be large enough for pointer accuracy (48dp minimum)

See Input Adaptation Reference for detailed guidance.

Step 3: Layout Adjustment

Panels are resizable and can have various aspect ratios. Your app must handle:

• Dynamic width and height changes
• Landscape and portrait orientations
• Different effective DPI values

Use responsive layout strategies such as ConstraintLayout or Jetpack Compose. See Panel Layout Reference.

Step 4: Gradle and Manifest Updates

Update your build configuration to target Horizon OS:

// build.gradle.kts
android {
    defaultConfig {
        minSdk = 29       // Android 10 minimum
        targetSdk = 34    // API 34 or higher required for all new 2D panel apps
    }
}

Add required manifest entries for device targeting. See Gradle Setup Reference.

Step 5: Input Testing

Test with all supported input methods:

• Controller: point-and-click, thumbstick scroll, trigger tap
• Hand tracking: pinch-to-select, hand scroll
• Keyboard/mouse: Bluetooth peripherals, system keyboard for text fields

Use the XR Simulator for rapid iteration, then validate on-device.

Step 6: Store Submission

Before submitting to the Horizon Store:

• Verify all Compatibility Requirements
• Test on at least Quest 3 and Quest 2 (if targeting both)
• Confirm the app works in both passthrough and immersive home environments
• Review Meta's content policies and technical requirements

Quick Compatibility Check

Works on Horizon OS

| Feature | Status | Notes | |---|---|---| | Standard Android Views | Supported | TextView, RecyclerView, etc. | | Jetpack Compose | Supported | Full Compose UI toolkit | | WebView | Supported | Chromium-based | | Media playback (ExoPlayer) | Supported | Video and audio | | Networking (HTTP, WebSocket) | Supported | Wi-Fi connectivity | | Room / SQLite | Supported | Local database | | WorkManager | Supported | Background tasks | | Notifications | Supported | Horizon OS notification panel | | Bluetooth (peripherals) | Supported | Keyboard, mouse, gamepad | | Android Accessibility APIs | Supported | TalkBack equivalent available |

Restricted or Unavailable

| Feature | Status | Notes | |---|---|---| | Camera (front-facing) | Not available | No standard camera in 2D mode | | Telephony / SMS | Not available | No cellular radio | | NFC | Not available | No NFC hardware | | GPS / Fine location | Limited | Wi-Fi-based location only | | Fingerprint / BiometricPrompt | Not available | Use Meta account auth instead | | Split-screen (multi-window) | Limited | Use Spatial SDK panels instead | | Google Play Services | Not available | Use Meta equivalents or alternatives | | ARCore | Not available | Use Meta Spatial SDK for spatial features | | Multi-touch gestures | Limited | Single pointer from controller |

Common Issues and Fixes

| Issue | Cause | Fix | |---|---|---| | App crashes on launch | Missing Google Play Services dependency | Remove or make GMS optional | | Buttons too small to tap | Touch targets under 48dp | Increase minimum tap target size | | No scroll in lists | Swipe-based scroll not triggered | Ensure RecyclerView/LazyColumn handles generic scroll events | | Keyboard doesn't appear | Custom input field not using InputConnection | Use standard EditText or TextField | | Layout broken | Fixed-size layout assumptions | Use responsive layouts with ConstraintLayout or Compose | | App requests unavailable permissions | Camera, telephony, etc. | Guard with hasSystemFeature() checks | | APK rejected for prohibited permissions | Library or plugin silently added a prohibited permission | Run aapt dump permissions your-app.apk, then check prohibited list | | APK rejected for invalid signature | Signed with v1-only scheme | v2 signing is default in AGP 7.0+; for older AGP, add v2SigningEnabled = true to your signing config |

Key Concepts

Compatibility Mode vs Native Targeting

Apps not specifically targeting Horizon OS run in compatibility mode:

• Fixed panel size (simulating a phone screen)
• Limited resizing
• Basic input translation

Apps that target Horizon OS with proper manifest entries run in native mode:

• Resizable panels
• Full input API support
• Access to Spatial SDK features (optional)
• Better integration with Horizon OS shell

Testing Tools

• hzdb: Command-line tool for installing, launching, and debugging apps on Quest
• XR Simulator: Desktop tool for testing Quest apps without a headset
• Meta Quest Developer Hub (MQDH): GUI tool for device management and debugging
• Android Studio: Full IDE with Quest device support via ADB

Performance Considerations

Quest devices have mobile-class hardware with strict thermal limits:

• GPU: Qualcomm Adreno (varies by Quest model)
• RAM: 6-12 GB shared between system and apps
• Thermal: Sustained workloads may trigger thermal throttling
• Avoid heavy overdraw and complex shader effects in 2D UI
• Minimize background work to reduce power consumption
• Test with representative data loads (large lists, images, etc.)

References

• Compatibility Requirements -- store requirements and API compatibility
• Input Adaptation -- adapting touch to controller and hand input
• Panel Layout -- responsive layout for Horizon OS panels
• Gradle Setup -- build configuration and manifest entries