Building APKs

Prerequisites: Android SDK + NDK, Ubuntu/WSL build tools (git, zip, openjdk-17-jdk, autoconf, …). Tooling already downloaded by buildozer lives under ~/.buildozer/android/platform/ by default.

A practical workflow is to iterate on the app logic first, then only change the packaging layer when you need a new dependency or a different build setting. In most cases that means editing p4a_app/boot.py (startup / PYDEVICES_*), p4a_app/main.py / launcher.py (user entry), and p4a_app/buildozer.spec or p4a_recipes/ when the APK’s runtime package list changes. Display wiring comes from TestPyPI pydevices-desktop (board_config + pure-Python usdl2); do not add a local board_config.py that shadows it.

./build_android.sh              # prompts for launcher title (Enter = current)
./build_android.sh -y           # keep current title (CI / automation)
./build_android.sh --title Paint
# APK: p4a_app/bin/launcher-0.5.0-*-debug.apk (name may vary)
./scripts/emulator.sh

build_android.sh creates .venv/ and installs host deps from requirements-dev.txt. It rsyncs sibling pydevices-examples/lib/utils/ into p4a_app/utils/, then overlays canonical pydevices/utils/mip.py. Override the sources with PYDEVICES_EXAMPLES_UTILS and PYDEVICES_PRODUCT_ROOT. Runtime distributions (pydevices-displaydev, pydevices-desktop, …) come from TestPyPI via p4a_recipes/. For local iteration only, pass --local-modules (or ANDROID_DEBUG_LOCAL_MODULES=1) to shadow the displaydev/, usdl2.py, and audiodev/ imports from sibling checkouts into p4a_app/; default builds remove those shadows. Package id: org.pydevices.launcher. Launcher label comes from title in p4a_app/buildozer.spec (PyDevices Launcher).

p4a_app/stdio_sidecar.py (started from boot.py) listens on localhost so scripts/android.sh can attach this terminal as the app’s stdin/stdout/stderr, including -i for a MicroPython-style REPL. build_android.sh patches p4a’s getEntryPoint so the Activity runs boot.py before optional user main.py (upstream sdl2 otherwise hardcodes main.py).

Icon and presplash

buildozer.spec points both at the same asset:

icon.filename = %(source.dir)s/icon.png
presplash.filename = %(source.dir)s/icon.png

Spec	Details
File	p4a_app/icon.png (default: copy of PyDevices logo-512.png)
Format	PNG, square, RGBA preferred
Size	512×512 (buildozer resizes into density buckets)
icon	Launcher / home-screen icon
presplash	Startup splash while Python/SDL bootstrap

Replace icon.png (or change the paths) and rebuild for a new look.

Desktop smoke test (Xvfb)

./scripts/test_desktop.sh

Emulator / phone

./scripts/emulator.sh          # AVD already running (WSL → use Windows AVD + adb.exe)
./scripts/phone.sh             # USB-connected phone (skips emulators)

On WSL, start the AVD from Windows (Device Manager ▶), then talk to it with Windows adb.exe (e.g. a ~/bin/adb.exe symlink to %LOCALAPPDATA%\Android\Sdk\platform-tools\adb.exe).

USB debugging on a Samsung phone (One UI)

USB debugging is hidden until Developer options are unlocked, and Samsung Auto Blocker can leave it greyed out (“blocked by auto blocker”).

1. Settings → About phone → Software information → tap Build number seven times (unlock Developer options).
2. If USB debugging says blocked by Auto Blocker:
   • Settings → Security and privacy → Auto Blocker → turn the main switch off (PIN/fingerprint if asked).
3. Settings → Developer options → enable USB debugging → OK.
4. Plug in a data USB cable; accept Allow USB debugging? on the phone.
5. Confirm from WSL: adb.exe devices shows a non-emulator-* line as device, then run ./scripts/phone.sh.

You can turn Auto Blocker back on afterward; USB debugging may be blocked again until you disable it.

Android SDK Command-line Tools (sdkmanager)

A Studio-installed SDK often has no cmdline-tools/ folder until you add it. Without that package there is no sdkmanager.bat for CLI image installs.

1. Android Studio → Settings → Languages & Frameworks → Android SDK → SDK Tools
2. Check Android SDK Command-line Tools (latest) → Apply
3. The batch file lands at:

%LOCALAPPDATA%\Android\Sdk\cmdline-tools\latest\bin\sdkmanager.bat

From WSL that path is typically:

/mnt/c/Users/<you>/AppData/Local/Android/Sdk/cmdline-tools/latest/bin/sdkmanager.bat

Example (AMD64 Windows — use an x86_64 system image, not arm64):

"%LOCALAPPDATA%\Android\Sdk\cmdline-tools\latest\bin\sdkmanager.bat" ^
  "system-images;android-37.1;google_apis_playstore_ps16k;x86_64"

An arm64 AVD on AMD64 Windows exits immediately (“emulator process for AVD … has terminated”). Until cmdline-tools are installed, download images from Studio’s Device Manager / SDK Manager UI instead.

Your own app

Almost everything a user customizes for their APK lives under p4a_app/:

Customize	Where
Entry / demo code	p4a_app/main.py, launcher.py (or stage examples via scripts/android.sh); startup in boot.py
Display size / rotation / scale	PYDEVICES_* env in boot.py (or board_config_tv.py from main.py for TV)
Title, package id, orientation, version, permissions, requirements	p4a_app/buildozer.spec
Icon / presplash	p4a_app/icon.png (paths in the spec)

Leave p4a_app/ alone only when you need packaging or host tooling changes:

Need	Where
New / different CPython wheel install from TestPyPI	p4a_recipes/ (+ list the recipe name in buildozer.spec requirements)
Build / install / smoke helpers	build_android.sh, scripts/

Keep p4a.local_recipes pointed at this repo’s p4a_recipes/ unless you are shipping your own recipe tree.