hz-android-2d-porting

name	hz-android-2d-porting
license	Apache-2.0
description	Guides porting existing Android 2D apps to Meta Quest and Horizon OS — input adaptation, panel layout, and design requirements. Use when adapting a mobile Android app for Quest.
allowed-tools	Bash(metavr:*) Bash(hzdb:*)

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 metavr (the Quest device CLI) via metavr <args>. The command is published as the npm package metavr, so if metavr is not on PATH you can run the same CLI via npx -y metavr <args> — no global install needed; npx fetches the latest published version on demand.

The examples in this doc call metavr directly; the npx -y metavr <args> form above is the equivalent when metavr is not on PATH (the published npm package is still metavr).

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

metavr app install path/to/your-app.apk
metavr 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

• metavr: 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