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DarkRoom/docker/android/README.md
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dtourolleandClaude Opus 5 eaafacc3fb Give the phone the model it had no way to obtain
Face indexing was compiled into the APK all along — dr-ui takes dr-face with
`inference` on every target, so SCRFD, alignment, MBF, calibration and
clustering were all in there. What was missing was the weights, and on Android
there was no way to supply them.

Route C (docs/faces.md §2.2) says the user obtains the model and the app loads
it. On a desktop that is a real gesture: drop two files in
~/.local/share/darkroom/models/ and indexing starts working. On Android it is
not a gesture at all. `internal_data_path` is app-private, `run-as` needs a
debuggable build, and the in-app fetch route C specifies was never built — so
the settings page reported "no face model is installed" on every launch with
nothing behind the message. Not "off until you supply weights"; off.

So the shape-fixed pair goes into LFS under the APK's assets, assemble-apk.sh
copies it into the package, and `android_main` unpacks it to the shared models
directory before anything asks whether a model is present.

Three things that are not incidental:

The models directory is now shared across accounts rather than per-account.
Weights are identified by `faces.model_id`, not by who is signed in, so two
accounts had no reason to hold two copies — and the unpack runs before any
session exists to key a per-account path off. `face_models` still prefers a
per-account directory when one is populated, so anyone mid-migration keeps the
ability to pin one library to its own pair.

The unpack writes under a temporary name and renames. `face_models` decides
availability on `is_file()` alone, so a copy truncated by the process being
killed would leave a file that passes that test and fails inside tract —
reported to the user as a broken model rather than a missing one.

assemble-apk.sh refuses an LFS pointer. At ~130 bytes it looks exactly like a
model to `cp`, and unchecked it reaches the device and fails in the graph
loader instead of telling someone to run `git lfs pull` — the same guard
dr-segment's build script applies to yolo26n-seg.onnx.

The licensing half is unchanged and recorded in §2.2a: the InsightFace grant is
research-only, this is a private repository and a self-installed build, and
these files come back out before anything is published. The weights are still
not a cargo build input — dr-face has no `models/` directory and no
`embedded-model` feature, and nothing in the build reads them. The APK assembly
step copies two files and is the only thing in the tree that knows they exist.

Verified on device: both models unpack on first launch (2524817 and 13616095
bytes) and the APK carries them at assets/models/.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-27 13:18:07 +02:00

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3.9 KiB
Markdown

# Android build environment
Reproducible container for cross-compiling DarkRoom to Android. CI and local builds use the same
image, so a break appears in one place rather than two.
## Use
```bash
# Cross-compile for a device ABI
./docker/android/build.sh cargo ndk -t arm64-v8a build --release
# All four ABIs
./docker/android/build.sh cargo ndk -t arm64-v8a -t armeabi-v7a -t x86_64 -t x86 build --release
# Type-check without linking
./docker/android/build.sh cargo check --target aarch64-linux-android
# Interactive shell
./docker/android/build.sh
# After editing the Dockerfile
./docker/android/build.sh --rebuild
```
Prefers `podman`, falls back to `docker`. First run builds the image, which takes several minutes;
after that it is cached.
## In CI
`.gitea/workflows/android-image.yml` builds this image and pushes it to
`gitea.tourolle.paris/dtourolle/darkroom-android`, which the Android job then runs inside. It is
called on every push and finishes in seconds unless something here changed — the image is tagged
with the git tree hash of `docker/android/`, so a rebuild happens when and only when a file in this
directory does.
Nothing needs pushing by hand. Editing the Dockerfile is the trigger; `latest` follows
automatically. To force a rebuild without a content change, run the workflow from the Gitea UI with
`force` set to `true`.
The job runs on the host runner rather than in a container, because it needs the Docker daemon and
the runner host's cached registry credentials.
## Face models
`package.sh` bundles `apps/darkroom-android/android/assets/models/` into the APK, and the entry point
unpacks it on first launch. **The models are in LFS**, so a clone without `git lfs pull` has 130-byte
pointers there; the build detects that and stops rather than shipping them.
This exists because Android offers no other route to a model: the directory the app reads from is
inside app-private storage, `run-as` needs a debuggable build, and the app has no picker and no
fetch. docs/faces.md §2.2a is the decision and its limits — these files come back out before anything
is published.
## Pinned versions
| Component | Version | Why this one |
|---|---|---|
| JDK | 17 | AGP's stable target. The host's JDK 25 breaks Gradle. |
| Compile SDK | API 36 | Required for Play distribution |
| **Min API** | **28** (Android 9) | Floor where Vulkan support is dependable (NFR-COMPAT-1) |
| Build tools | 36.0.0 | Matches compile SDK |
| NDK | 27.2.12479018 (r27c) | Current LTS |
| Rust | 1.92.0 | Slint 1.17 requires it; cargo-ndk 4.1.x needs ≥ 1.86 |
| cargo-ndk | 4.1.2 | |
Bumping any of these is a reviewable change, not silent drift.
### Compile SDK versus min API
These are different and both matter. `ANDROID_API` (36) is what the SDK compiles against — the
newest APIs available. `MIN_API` (28) is what native code *links* against, and determines the
oldest device that can run the result.
cargo-ndk defaults to **API 21** if not told otherwise, which is far below what this app needs.
`CARGO_NDK_PLATFORM` and the per-target linker paths both pin it to `MIN_API`. Verify with:
```bash
file target/aarch64-linux-android/release/*.so
# → "... for Android 28, built by NDK r27c"
```
## Caching
The cargo registry and target directory persist in `~/.cache/darkroom-android`, so rebuilds do not
re-download the crate index. Clear with:
```bash
rm -rf ~/.cache/darkroom-android
```
The Android target dir is kept separate from the host's `target/` — sharing one directory between
host and container builds causes constant rebuilds as they invalidate each other's fingerprints.
## What is not here
No emulator, no `adb` device access. This image cross-compiles; it does not run or deploy. Device
testing (spikes S2 and S10, which need two GPU vendors) happens on real hardware — the emulator's
GPU behaviour is not representative of Adreno or Mali, which is precisely what those spikes exist
to test.