feat(android): follow the activity lifecycle and build an APK (Issue #42)

- The drawing surface is created once the native window exists (Resumed)
  and released when the app goes to the background (Suspended); before
  that everything is saved, as Android may stop the app at any time
- Android's back button acts like Escape instead of closing the app
- Panics are written to logcat; no update check on Android yet
- scripts/package-android.sh builds target/ink-notes_<version>_arm64.apk
  without Gradle (NDK, aapt2, zipalign, apksigner); signing key from
  ANDROID_KEYSTORE/ANDROID_KEYSTORE_PASS/ANDROID_KEY_ALIAS, otherwise
  the debug key

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Cargo.toml

@@ -69,7 +69,7 @@ wayland-backend = { version = "0.3", features = ["client_system"] }
 wayland-protocols = { version = "0.31", features = ["client", "unstable"] }
 
 # Android (Issue #42): winit bound to the native activity. The library is built as
-# cdylib with `cargo rustc --lib --crate-type cdylib --target aarch64-linux-android`
+# cdylib and packed into an APK by scripts/package-android.sh
 [target.'cfg(target_os = "android")'.dependencies]
 winit = { version = "0.29", features = ["rwh_06", "android-native-activity"] }
 android_logger = { version = "0.13", default-features = false }

README.de.md

@@ -156,7 +156,7 @@ Die CI prüft zusätzlich `cargo fmt --check` und `cargo clippy --all-targets --
 
 Andere Systeme:
 - **Windows** wird unter Linux übersetzt: `scripts/package-windows.sh` (braucht `gcc-mingw-w64-x86-64`); die Tests laufen mit `wine` als Runner (`CARGO_TARGET_X86_64_PC_WINDOWS_GNU_RUNNER=wine cargo test --target x86_64-pc-windows-gnu`).
-- **Android** (in Arbeit, Issue #42): `cargo check --target aarch64-linux-android` und `cargo rustc --lib --crate-type cdylib --target aarch64-linux-android` mit dem NDK-Compiler in `CC_aarch64_linux_android`. Dort startet die App noch nicht: Die Fensterfläche muss erst dem Lebenszyklus der Activity folgen.
+- **Android** (experimentell, Issue #42): `scripts/package-android.sh` baut `target/ink-notes_<version>_arm64.apk` ohne Gradle. Nötig sind das Android-SDK (build-tools, Plattform 34; `ANDROID_HOME`, Standard `~/android-sdk`) und das NDK; der Signierschlüssel kommt aus `ANDROID_KEYSTORE`, `ANDROID_KEYSTORE_PASS` und `ANDROID_KEY_ALIAS`, sonst wird der Debug-Schlüssel verwendet. Installieren mit `adb install -r target/ink-notes_<version>_arm64.apk`, Log-Ausgaben mit `adb logcat -s ink-notes`. Notizbücher bleiben vorerst in der App; Stifterkennung, Bildschirmtastatur und Dateidialoge fehlen noch.
 
 ### Projektstruktur
 

README.md

@@ -156,7 +156,7 @@ CI additionally checks `cargo fmt --check` and `cargo clippy --all-targets -- -D
 
 Other systems:
 - **Windows** is cross-compiled on Linux: `scripts/package-windows.sh` (needs `gcc-mingw-w64-x86-64`); the tests run with `wine` as runner (`CARGO_TARGET_X86_64_PC_WINDOWS_GNU_RUNNER=wine cargo test --target x86_64-pc-windows-gnu`).
-- **Android** (in progress, Issue #42): `cargo check --target aarch64-linux-android` and `cargo rustc --lib --crate-type cdylib --target aarch64-linux-android` with the NDK compiler in `CC_aarch64_linux_android`. The app does not start there yet: the window surface still has to follow the activity lifecycle.
+- **Android** (experimental, Issue #42): `scripts/package-android.sh` builds `target/ink-notes_<version>_arm64.apk` without Gradle. It needs the Android SDK (build-tools, platform 34; `ANDROID_HOME`, default `~/android-sdk`) and the NDK; the signing key comes from `ANDROID_KEYSTORE`, `ANDROID_KEYSTORE_PASS` and `ANDROID_KEY_ALIAS`, otherwise the debug key is used. Install with `adb install -r target/ink-notes_<version>_arm64.apk`, log output with `adb logcat -s ink-notes`. Notebooks stay inside the app for now; pen detection, on-screen keyboard and file dialogs are still missing.
 
 New code comments and commit messages are written in English; older code and history still contain German.
 

packaging/android/AndroidManifest.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Manifest of the Android app (Issue #42). scripts/package-android.sh fills in the version.
+     NativeActivity loads libink_notes.so, whose android_main runs the app. -->
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="eu.pansi.inknotes"
+    android:versionCode="@VERSION_CODE@"
+    android:versionName="@VERSION@">
+
+    <uses-feature android:name="android.hardware.touchscreen" android:required="false" />
+
+    <application
+        android:label="ink-notes"
+        android:icon="@mipmap/ic_launcher"
+        android:hasCode="false"
+        android:extractNativeLibs="true"
+        android:theme="@android:style/Theme.Material.Light.NoActionBar">
+        <!-- configChanges: rotating the tablet or attaching a keyboard must not restart the
+             activity; the app adapts to the new window size itself -->
+        <activity
+            android:name="android.app.NativeActivity"
+            android:exported="true"
+            android:launchMode="singleTask"
+            android:configChanges="orientation|screenSize|smallestScreenSize|screenLayout|keyboard|keyboardHidden|navigation|density|uiMode|fontScale|locale|layoutDirection">
+            <meta-data android:name="android.app.lib_name" android:value="ink_notes" />
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

scripts/package-android.sh

@@ -0,0 +1,94 @@
+#!/usr/bin/env bash
+# ==============================================================================
+# Builds the Android app target/ink-notes_<version>_arm64.apk (Issues #42, #45)
+# without Gradle: the Rust library is built as cdylib with the NDK, aapt2 links the
+# manifest and the icon, zipalign and apksigner finish the APK.
+#
+# Needs the Android SDK (build-tools, platform android-34) and the NDK:
+#   ANDROID_HOME      SDK folder (default: ~/android-sdk)
+#   ANDROID_NDK_HOME  NDK folder (default: newest in $ANDROID_HOME/ndk)
+#
+# Signing key (all three, otherwise the debug key ~/.android/debug.keystore is used and
+# created if missing; such an APK is only meant for testing):
+#   ANDROID_KEYSTORE, ANDROID_KEYSTORE_PASS, ANDROID_KEY_ALIAS
+# ==============================================================================
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+ROOT_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+cd "${ROOT_DIR}"
+
+TARGET="aarch64-linux-android"
+ABI="arm64-v8a"
+MIN_SDK=26
+TARGET_SDK=34
+VERSION=$(grep -m1 '^version = ' Cargo.toml | cut -d '"' -f2)
+IFS=. read -r MAJOR MINOR PATCH <<<"${VERSION%%-*}"
+VERSION_CODE=$((MAJOR * 10000 + MINOR * 100 + PATCH))
+APK_NAME="ink-notes_${VERSION}_arm64.apk"
+
+ANDROID_HOME="${ANDROID_HOME:-${HOME}/android-sdk}"
+if [ -z "${ANDROID_NDK_HOME:-}" ]; then
+    ANDROID_NDK_HOME=$(ls -d "${ANDROID_HOME}"/ndk/*/ 2>/dev/null | sort -V | tail -n1)
+fi
+BUILD_TOOLS=$(ls -d "${ANDROID_HOME}"/build-tools/*/ 2>/dev/null | sort -V | tail -n1)
+ANDROID_JAR="${ANDROID_HOME}/platforms/android-${TARGET_SDK}/android.jar"
+NDK_BIN="${ANDROID_NDK_HOME%/}/toolchains/llvm/prebuilt/linux-x86_64/bin"
+
+for needed in "${NDK_BIN}/${TARGET}${MIN_SDK}-clang" "${BUILD_TOOLS}aapt2" "${ANDROID_JAR}"; do
+    if [ ! -e "${needed}" ]; then
+        echo "FEHLER: ${needed} nicht gefunden (Android-SDK/NDK, siehe Kopf des Skripts)."
+        exit 1
+    fi
+done
+if command -v rustup >/dev/null 2>&1; then
+    rustup target add "${TARGET}"
+fi
+
+echo "=== [1/4] Baue libink_notes.so (${TARGET}) ==="
+export CC_aarch64_linux_android="${NDK_BIN}/${TARGET}${MIN_SDK}-clang"
+export AR_aarch64_linux_android="${NDK_BIN}/llvm-ar"
+export CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER="${NDK_BIN}/${TARGET}${MIN_SDK}-clang"
+cargo rustc --release --lib --crate-type cdylib --target "${TARGET}"
+LIB="${CARGO_TARGET_DIR:-target}/${TARGET}/release/libink_notes.so"
+
+echo "=== [2/4] Ressourcen und Manifest ==="
+WORK="target/android-apk"
+rm -rf "${WORK}"
+mkdir -p "${WORK}/res/mipmap-xxxhdpi" "${WORK}/compiled" "${WORK}/apk/lib/${ABI}"
+cp assets/ink-notes.png "${WORK}/res/mipmap-xxxhdpi/ic_launcher.png"
+sed -e "s/@VERSION_CODE@/${VERSION_CODE}/" -e "s/@VERSION@/${VERSION}/" \
+    packaging/android/AndroidManifest.xml >"${WORK}/AndroidManifest.xml"
+"${BUILD_TOOLS}aapt2" compile --dir "${WORK}/res" -o "${WORK}/compiled/res.zip"
+"${BUILD_TOOLS}aapt2" link -o "${WORK}/unaligned.apk" -I "${ANDROID_JAR}" \
+    --manifest "${WORK}/AndroidManifest.xml" \
+    --min-sdk-version "${MIN_SDK}" --target-sdk-version "${TARGET_SDK}" \
+    "${WORK}/compiled/res.zip"
+
+echo "=== [3/4] Native Bibliothek hinzufügen ==="
+cp "${LIB}" "${WORK}/apk/lib/${ABI}/"
+(cd "${WORK}/apk" && zip -q -r ../unaligned.apk lib)
+"${BUILD_TOOLS}zipalign" -f -p 4 "${WORK}/unaligned.apk" "${WORK}/aligned.apk"
+
+echo "=== [4/4] Signieren ==="
+if [ -n "${ANDROID_KEYSTORE:-}" ] && [ -n "${ANDROID_KEYSTORE_PASS:-}" ] && [ -n "${ANDROID_KEY_ALIAS:-}" ]; then
+    KEYSTORE="${ANDROID_KEYSTORE}"
+    KEY_ALIAS="${ANDROID_KEY_ALIAS}"
+    export KS_PASS="${ANDROID_KEYSTORE_PASS}"
+else
+    KEYSTORE="${HOME}/.android/debug.keystore"
+    KEY_ALIAS="androiddebugkey"
+    export KS_PASS="android"
+    if [ ! -f "${KEYSTORE}" ]; then
+        mkdir -p "$(dirname "${KEYSTORE}")"
+        keytool -genkeypair -keystore "${KEYSTORE}" -storepass android -keypass android \
+            -alias androiddebugkey -keyalg RSA -keysize 2048 -validity 10000 \
+            -dname "CN=Android Debug,O=Android,C=US"
+    fi
+    echo "Hinweis: Signiert mit dem Debug-Schlüssel ${KEYSTORE} (nur zum Testen)."
+fi
+"${BUILD_TOOLS}apksigner" sign --ks "${KEYSTORE}" --ks-key-alias "${KEY_ALIAS}" \
+    --ks-pass env:KS_PASS --key-pass env:KS_PASS \
+    --out "target/${APK_NAME}" "${WORK}/aligned.apk"
+"${BUILD_TOOLS}apksigner" verify "target/${APK_NAME}"
+ls -lh "target/${APK_NAME}"

src/canvas.rs

@@ -165,7 +165,10 @@ struct NeighborPage {
 }
 
 pub struct CanvasState {
-    pub surface: wgpu::Surface<'static>,
+    /// Drawing surface of the window; `None` while the app is in the background on Android
+    /// (the native window only exists between `Resumed` and `Suspended`)
+    surface: Option<wgpu::Surface<'static>>,
+    instance: wgpu::Instance,
     /// Verwendeter Grafikadapter (für erneute Abfrage der Surface-Fähigkeiten bei Größenänderung)
     adapter: wgpu::Adapter,
     /// Multisampling der Zeichenfläche (1 = aus) und das zugehörige Zwischenbild
@@ -591,7 +594,8 @@ impl CanvasState {
         let egui_renderer = egui_wgpu::Renderer::new(&device, render_format(&config), None, 1);
 
         Ok(Self {
-            surface,
+            surface: Some(surface),
+            instance,
             adapter,
             msaa_samples,
             msaa_view,
@@ -727,14 +731,42 @@ impl CanvasState {
         self.update_uniforms();
     }
 
+    /// Releases the drawing surface: on Android the native window goes away when the app
+    /// is sent to the background (`Event::Suspended`). Drawing is skipped until [`Self::resume`].
+    pub fn suspend(&mut self) {
+        self.surface = None;
+    }
+
+    /// Creates the drawing surface again for the window (`Event::Resumed` on Android).
+    pub fn resume(&mut self, window: Arc<Window>) -> Result<(), Box<dyn std::error::Error>> {
+        if self.surface.is_some() {
+            return Ok(());
+        }
+        let surface = self.instance.create_surface(window.clone())?;
+        if !surface
+            .get_capabilities(&self.adapter)
+            .formats
+            .contains(&self.config.format)
+        {
+            return Err("surface format changed".into());
+        }
+        self.surface = Some(surface);
+        // Configures the new surface (the window may have changed size meanwhile)
+        self.resize(window.inner_size());
+        Ok(())
+    }
+
     /// Passt die Surface und Projektionsmatrizen an eine neue Fenstergröße an.
     pub fn resize(&mut self, new_size: PhysicalSize<u32>) {
         if new_size.width > 0 && new_size.height > 0 {
             self.size = new_size;
             self.config.width = new_size.width;
             self.config.height = new_size.height;
+            let Some(surface) = &self.surface else {
+                return;
+            };
             // Fähigkeiten neu abfragen: Ein nicht (mehr) angebotener Modus führt in wgpu zum Absturz
-            let caps = self.surface.get_capabilities(&self.adapter);
+            let caps = surface.get_capabilities(&self.adapter);
             if !caps.present_modes.contains(&self.config.present_mode) {
                 match choose_present_mode(&caps.present_modes) {
                     Some(mode) => self.config.present_mode = mode,
@@ -750,7 +782,7 @@ impl CanvasState {
                     }
                 }
             }
-            self.surface.configure(&self.device, &self.config);
+            surface.configure(&self.device, &self.config);
             self.msaa_view = create_msaa_view(&self.device, &self.config, self.msaa_samples);
             self.stencil_view = create_stencil_view(&self.device, &self.config, self.msaa_samples);
             self.recalculate_viewport();
@@ -1386,7 +1418,13 @@ impl CanvasState {
                 .update_texture(&self.device, &self.queue, *id, image_delta);
         }
 
-        let output = self.surface.get_current_texture()?;
+        let Some(surface) = &self.surface else {
+            for id in &textures_delta.free {
+                self.egui_renderer.free_texture(id);
+            }
+            return Ok(());
+        };
+        let output = surface.get_current_texture()?;
         let view = output.texture.create_view(&wgpu::TextureViewDescriptor {
             format: Some(render_format(&self.config)),
             ..Default::default()

src/lib.rs

@@ -38,9 +38,7 @@ pub mod xopp;
 
 /// Entry point on Android (Issue #42), called by the native activity.
 ///
-/// Builds with `cargo rustc --lib --crate-type cdylib --target aarch64-linux-android`. Not
-/// usable yet: the window surface still has to be created on `Resumed` and dropped on
-/// `Suspended`.
+/// `scripts/package-android.sh` builds the library and packs it into an APK.
 #[cfg(target_os = "android")]
 #[no_mangle]
 fn android_main(app: winit::platform::android::activity::AndroidApp) {
@@ -51,6 +49,8 @@ fn android_main(app: winit::platform::android::activity::AndroidApp) {
             .with_max_level(log::LevelFilter::Info)
             .with_tag("ink-notes"),
     );
+    // Panics would otherwise only go to stderr, which Android discards
+    std::panic::set_hook(Box::new(|info| log::error!("{info}")));
     if let Some(dir) = app.internal_data_path() {
         paths::set_app_dir(dir);
     }

src/platform.rs

@@ -82,6 +82,51 @@ pub fn desktop_event_loop() -> Result<winit::event_loop::EventLoop<()>, winit::e
     builder.build()
 }
 
+/// Waits until the window can be drawn to. On Android the native window only exists after
+/// `Event::Resumed` (Issue #42); on the desktop it is there right away.
+pub fn wait_until_resumed(
+    #[allow(unused_variables)] event_loop: &mut winit::event_loop::EventLoop<()>,
+) {
+    #[cfg(target_os = "android")]
+    {
+        use winit::event::Event;
+        use winit::platform::pump_events::{EventLoopExtPumpEvents, PumpStatus};
+        let mut resumed = false;
+        while !resumed {
+            let status = event_loop.pump_events(None, |event, _| {
+                if matches!(event, Event::Resumed) {
+                    resumed = true;
+                }
+            });
+            if let PumpStatus::Exit(_) = status {
+                std::process::exit(0);
+            }
+        }
+    }
+}
+
+/// Runs the event loop until the app quits. On Android the loop was already started by
+/// [`wait_until_resumed`], so it is driven with `pump_events` (`run` would refuse to start).
+pub fn run_event_loop<F>(
+    #[allow(unused_mut)] mut event_loop: winit::event_loop::EventLoop<()>,
+    #[allow(unused_mut)] mut handler: F,
+) -> Result<(), winit::error::EventLoopError>
+where
+    F: FnMut(winit::event::Event<()>, &winit::event_loop::EventLoopWindowTarget<()>),
+{
+    #[cfg(target_os = "android")]
+    {
+        use winit::platform::pump_events::{EventLoopExtPumpEvents, PumpStatus};
+        loop {
+            if let PumpStatus::Exit(_) = event_loop.pump_events(None, &mut handler) {
+                return Ok(());
+            }
+        }
+    }
+    #[cfg(not(target_os = "android"))]
+    event_loop.run(handler)
+}
+
 /// Gives the window the app id (Wayland: app_id, X11: WM_CLASS), so that dock and task bar
 /// show the app icon for it.
 pub fn with_app_id(