Retra

A modern open-source Android emulator built around mGBA, focused on a polished Game Boy Advance experience.

Download Retra v1.0.4 · Changelog · Troubleshooting · Contributing

About Retra

Retra is an open-source Android retro emulator built around the mGBA core, with feature development primarily focused on Game Boy Advance gameplay.

It combines emulation with a mobile-first interface, persistent game data, customizable controls, backup and restore tools, save states, cheats, artwork, display customization, and local or remote GBA link features.

Important

Retra does not include commercial ROMs, BIOS files, or copyrighted game assets. Use only content you are legally permitted to use.

Features

Emulation & gameplay

GB, GBC, and GBA emulation through the mGBA integration.
Fast-forward and slow-motion speed controls.
Adaptive high-refresh interface presentation, with gameplay using a stable cadence-compatible 60/120 Hz presentation path while emulation timing remains independent from display refresh rate.
BIOS support, ROM patches, cheats, statistics, and per-ROM configuration.
Optional GLSL shaders and gameplay Color Style presets.

v1.0.4 SmoothTurbo hardening

Four-buffer latest-frame mailbox with dedicated producer, pending, rendering, and spare roles.
Allocation-free producer and GL-consumer result holders during normal gameplay.
Stale turbo frames are dropped instead of queued, so high-speed emulation does not create a visual catch-up backlog.
Fractional TurboSlicePlanner scheduling keeps 2×/4×/8×/16× timing smooth against the GBA's ~59.73 Hz base cadence.
Hitch-safe cumulative turbo timing re-anchors after substantial Android/GC stalls instead of paying the delay back as a burst.
Native speed-aware FIR audio keeps high-speed PCM work out of the Kotlin/JNI hot path, with deterministic reset when the speed multiplier changes.
VSync scheduling reuses callback Runnables, coalesces real mailbox generations, and resets generation state for each new gameplay session.

Saves & persistent data

Battery saves, save states, and automatic resume.
Gameplay Import save accepts both .sav and .srm battery-save files with per-ROM filename and save-size safety checks.
Persistent ROM identity based on SHA-256 content hashes.
Compatible saves and metadata can reconnect after a ROM is moved, renamed, removed, or re-imported.
Portable Create Backup and Restore Backup using .retra files.
Android Auto Backup/device transfer support.
Reinstall continuity through Android's Keep app data flow.

Controls & interface

Screen Editor with independent portrait and landscape layouts.
Draggable and resizable on-screen controls.
Emulator-screen resizing and edge-aware layout editing.
Controller opacity controls.
Optional light controller tap sound and smooth haptics under Sound.
Automatic artwork with persistent manual cover and background overrides.
Lightweight gameplay color presets: Classic, Vivid, Warm, and Muted.

Multiplayer & sync

GBA Local Link on one Android device.
Wi-Fi Remote Link between supported devices.
Bluetooth Remote Link between supported Android devices.
Google Drive sync with conflict-safe behavior.
Android Storage Access Framework folder fallback.

Updates & project quality

Automatic GitHub Releases update checks on each fresh app process, so newly published versions are discovered on the next launch.
Manual Check for updates action in About.
Modular Android architecture.
Release validation, regression tests, lint checks, and CI quality gates.

Download

The latest stable APK and release notes are available from:

Download Retra v1.0.4 →

Current stable release: Retra v1.0.4

Item	Current status
Version	`v1.0.4`
Release channel	Stable
Minimum Android	API 26 / Android 8.0+
License	Mozilla Public License 2.0
Maintainer	Zense
Emulator core	mGBA

Release history

Version	Summary
v1.0.0	Official release
v1.0.1	Added Create Backup and Restore Backup
v1.0.2	Added in-app update checking and Android reinstall-recovery hardening
v1.0.3	Added persistent ROM title editing plus controller, rewind, save-import, and Google Drive restore polish
v1.0.4	SmoothTurbo hardening: four-buffer latest-frame handoff, allocation-free gameplay hot paths, safer VSync/session recovery, and cleaner turbo audio transitions

Public release numbering follows Semantic Versioning. Earlier project work is organized in docs/DEVELOPMENT_HISTORY.md.

Color Style

Retra includes lightweight gameplay color presets that affect only the rendered game image. The Retra interface itself remains unchanged.

Available presets: Classic · Vivid · Warm · Muted

Multiplayer scope

Retra v1.0.4 supports normal GBA Link Cable-style multiplayer and two-player Local Single-Pak/Multiboot through:

Local Link on one Android device.
Single-Pak / Multiboot on one Android device using a user-provided 16 KiB GBA BIOS for the cartridge-less receiver.
Wi-Fi Remote Link between supported devices.
Bluetooth Remote Link between supported Android devices.

Remote Link includes connection health metrics, heartbeat/timeouts, state-hash validation, jitter-aware input delay, host-authoritative recovery, bounded recovery retries, and deterministic input reseeding.

Persistent game data

Retra separates replaceable ROM files from persistent user data.

ROM content -> SHA-256 -> permanent romId
                         |
                         +-- Saves
                         +-- Save states
                         +-- Cheats
                         +-- Layouts
                         +-- Covers/backgrounds
                         +-- Categories/favourites
                         +-- Statistics

Structured ROM metadata is stored with Room, application-wide settings use Preferences DataStore, and save commits use verified temporary files, per-ROM locking, and rotating backups.

Import recovery uses a durable journal so interrupted imports can be recovered safely.

For the full storage design, see docs/PERSISTENT_STORAGE_ARCHITECTURE.md.

Build from source

Requirements

Android Studio with the Android SDK required by the Gradle project.
The JDK/toolchain required by the included Android Gradle Plugin.
Android NDK r28.
CMake 3.22.1.
The exact locked mGBA source revision used by Retra.

Retra is pinned to mGBA commit:

543a197582c30364584d773a974d7f991892fa43

The revision is recorded in third_party/mgba.lock.

Prepare mGBA

python3 tools/prepare_mgba.py

This prepares third_party/mgba/ at the exact locked commit.

CMake also accepts the legacy sibling ../mgba/ location or an explicit RETRA_MGBA_SOURCE_DIR, but verifies that the source matches the clean locked revision before configuring the native build.

Android release metadata

versionName = 1.0.4
versionCode = 451
minSdk      = 26

versionCode 451 upgrades cleanly over v1.0.3 (450), v1.0.2 (449), v1.0.1 (448), and v1.0.0 (447).

Open and build

Clone or extract the Retra repository.
Run python3 tools/prepare_mgba.py.
Open the repository root in Android Studio.
Allow Gradle to sync and install the requested SDK, NDK, and CMake components.
Build and run on an Android device.

Command-line validation

Windows

gradlew.bat :app:compileDebugKotlin :app:testDebugUnitTest :app:lintDebug

macOS / Linux

./gradlew :app:compileDebugKotlin :app:testDebugUnitTest :app:lintDebug

A full APK/AAB build requires the exact mGBA revision recorded in third_party/mgba.lock. CMake rejects a different or dirty tracked checkout.

Repository structure

Retra/
├─ app/                         Android application
│  └─ src/main/
│     ├─ assets/retra/          WebView UI modules, styles, and branding
│     ├─ cpp/                   Native mGBA bridge and native build config
│     └─ java/.../emulator/     Android controllers, repositories, and runtime
├─ docs/                        Release, architecture, and engineering docs
│  └─ history/                  Archived implementation/build notes
├─ tests/                       Dependency-light regression tests
├─ third_party/                 Preferred project-local mGBA location
├─ tools/                       Release validation scripts
├─ CHANGELOG.md                 Public release and development history
├─ TROUBLESHOOTING.md           User troubleshooting and bug-reporting guide
├─ CONTRIBUTING.md              Contribution guide
├─ SECURITY.md                  Security policy
├─ THIRD_PARTY_NOTICES.md       Third-party licensing notices
└─ LICENSE                      MPL-2.0

See docs/README.md for the documentation index and docs/ARCHITECTURE.md for the current architecture.

Validation

Run the dependency-light release gate before publishing changes:

python3 tools/release_gate.py

It validates JavaScript syntax, regression tests, release structure, and release metadata that do not require the Android SDK/NDK or mGBA.

For Android-specific validation, also run the Gradle compile/test/lint tasks above.

Before publishing an APK/AAB, complete the physical-device checks in:

Documentation & support

CHANGELOG.md — public release and development history.
TROUBLESHOOTING.md — installation, ROM loading, performance, audio, controls, saves, backups, BIOS, multiplayer, sync, and crash-reporting help.
CONTRIBUTING.md — contribution requirements.
SECURITY.md — vulnerability reporting and security boundaries.
docs/DEVELOPMENT_HISTORY.md — organized pre-v1.0 development history.
docs/ARCHITECTURE.md — current Android/runtime architecture and module boundaries.
docs/CONTROLLER_FEEDBACK.md — controller sound/haptic behavior and design constraints.
docs/PERSISTENT_STORAGE_ARCHITECTURE.md — persistent storage design.

License

Retra source code is released under the Mozilla Public License 2.0 (MPL-2.0). See LICENSE.

Retra integrates with the separately maintained mGBA emulator core. mGBA is not owned by Retra and retains its own copyright and MPL-2.0 notices.

See THIRD_PARTY_NOTICES.md and the license files included with the exact mGBA revision used for your build.

ROMs, BIOS files, game artwork, trademarks, and game content are not distributed with Retra and remain the property of their respective rights holders.

Retra · Android retro emulation powered by mGBA

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Retra

About Retra

Features

Emulation & gameplay

v1.0.4 SmoothTurbo hardening

Saves & persistent data

Controls & interface

Multiplayer & sync

Updates & project quality

Download

Download Retra v1.0.4 →

Release history

Color Style

Multiplayer scope

Persistent game data

Build from source

Requirements

Prepare mGBA

Android release metadata

Open and build

Command-line validation

Repository structure

Validation

Documentation & support

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Name		Name	Last commit message	Last commit date
.github/workflows		.github/workflows
app		app
docs		docs
gradle		gradle
tests		tests
third_party		third_party
tools		tools
.gitignore		.gitignore
CHANGELOG.md		CHANGELOG.md
CONTRIBUTING.md		CONTRIBUTING.md
LICENSE		LICENSE
README.md		README.md
SECURITY.md		SECURITY.md
THIRD_PARTY_NOTICES.md		THIRD_PARTY_NOTICES.md
TROUBLESHOOTING.md		TROUBLESHOOTING.md
build.gradle.kts		build.gradle.kts
gradle.properties		gradle.properties
gradlew		gradlew
gradlew.bat		gradlew.bat
regression.yml		regression.yml
settings.gradle.kts		settings.gradle.kts

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Retra

About Retra

Features

Emulation & gameplay

v1.0.4 SmoothTurbo hardening

Saves & persistent data

Controls & interface

Multiplayer & sync

Updates & project quality

Download

Download Retra v1.0.4 →

Release history

Color Style

Multiplayer scope

Persistent game data

Build from source

Requirements

Prepare mGBA

Android release metadata

Open and build

Command-line validation

Repository structure

Validation

Documentation & support

License

About

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Security policy

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