android_translation_layer/README.md

A translation layer that allows running Android apps on a Linux system

![Angry Birds 3.2.0, Worms 2 Armageddon, and Gravity Defied running side by side by side](https://gitlab.com/android_translation_layer/android_translation_layer/-/raw/master/screenshot.png)
![Oculus Quest version of BeatSaber running on an aarch64 laptop](https://gitlab.com/android_translation_layer/android_translation_layer/-/raw/master/screenshot_2.png)

### Build
see [build documentation](https://gitlab.com/android_translation_layer/android_translation_layer/-/blob/master/doc/Build.md)

### Run in builddir
```sh
cd builddir
```
For an example of a full game working that can be distributed along this:
```sh
RUN_FROM_BUILDDIR= LD_LIBRARY_PATH=./ ./android-translation-layer /path/to/test_apks/org.happysanta.gd_29.apk -l org/happysanta/gd/GDActivity
```
Or for a sample app using OpenGL from native code to do it's rendering:
```sh
RUN_FROM_BUILDDIR= LD_LIBRARY_PATH=./ ./android-translation-layer path/to/test_apks/gles3jni.apk -l com/android/gles3jni/GLES3JNIActivity
```
Note: the test apks are available at https://gitlab.com/android_translation_layer/atl_test_apks.

### Run after installation
```sh
cd builddir
meson install
```

To run with the default data dir `~/.local/share/android_translation_layer/`:
```sh
android-translation-layer [path to apk] [-l activity to launch]
```
For custom data dir:
```sh
ANDROID_APP_DATA_DIR=[data dir] android-translation-layer [path to apk] [-l activity to launch]
```

### App data
As mentioned, the default data dir is `~/.local/share/android_translation_layer/`. The data for each
app is then stored in `~/.local/share/android_translation_layer/[apk-name]_`. What this means
in practice is that:
 - we pass this directory to the app where AOSP would pass `/data/data/[app-id]`, and extract native
libs in `lib/`
 - we pass this directory to the app where AOSP would pass `/storage/emulated/0` (this means OBBs
will be under `Android/obb/[app-id]/`, and various litter that the app would happily dump on the
"sdcard" on AOSP will end up here as well)
 - we pass this directory as an additional resource directory to `libandroidfw`, so you can
for example put something in `assets/file.txt` and if the app tries to load `assets/file.txt` from
it's apk file, it will be preferentially loaded from here instead (do note that some apps read files
from the apk by themselves, and some apps do weird things like only load the file in order to find
it's offset in the apk to then read it out by themselves, so not only will this not always work but
you will sometimes find out by having the app crash)
 - we extract some additional files from the apk here for our purposes

The reason that we don't use `[app-id]` for the directory name is simply that we don't have access
to the app id at an early enough point. However, this also allows you to have multiple versions
of the same app not clash. Feel free to rename the apk to `[app-id]_[version].apk`, or simply
`[app-id].apk` if you wish to replace it with a different version later and reuse the data dir.

### "install" an apk
You can pass `--install` on the cmdline to "install" an apk instead of launching it. This will copy
the apk to `_installed_apks_` in the data dir (`~/.local/share/android_translation_layer/` by default),
and use the xdp portal to install a `.desktop` file.

### Tweaks
##### Resolution Changes
Some apps don't like runtime changes to resolution. To sidestep this, we allow for specifying the initial resolution.
example with custom width/height:
```sh
android-translation-layer path/to/org.happysanta.gd_29.apk -l org/happysanta/gd/GDActivity -w 540 -h 960
```

#### Potential issues
- On X11, Gtk might decide to use GLX, which completely messes up our EGL-dependent code.
Use GDK_DEBUG=gl-egl to force the use of EGL.
- On Apple Silicon, the page size is non-standard. Upstream ART is only recently getting patches
to support such non-standard page size, so the version we use obviously doesn't have any. While there
will probably still be some issues with native libraries, you can work around the issue of AOT-compiled
code not working by adding `-X '-Xnoimage-dex2oat' -X '-Xusejit:false'` to the atl cmdline, which will
force the use of an interpreter. Make sure to clear `~/.cache/art/` since AOT-compiled oat files will
still be used if they were generated previously.

### Contribute
If you are trying to launch a random app, chances are that we are missing implementations for some stuff that it needs, and we also don't have (sufficiently real looking) stubs for the stuff it says it needs but doesn't really.

The workflow is basically to see where it fails (usually a Class or Method was not found) and to create stubs which sufficiently satisfy the app so that it continues trying to launch.

Once the app launches, you may find that some functionality (UI elements, ...) is missing. To enable such functionality, you need to convert the relevant stubs to actual implementation. You can look at simple widgets (e.g. TextView, or ImageView) to see how to implement a widget such that it shows up as a Gtk Widget.

For more specific instructions, see [doc/QuickHelp.md](https://gitlab.com/android_translation_layer/android_translation_layer/-/blob/master/doc/QuickHelp.md).  
For general description of the architecure, see [doc/Architecture.md](https://gitlab.com/android_translation_layer/android_translation_layer/-/blob/master/doc/Architecture.md).

If you want to contribute, and find the codebase overwhelming, don't hesitate to open an issue so we can help you out and possibly write more documentation.

### Roadmap

- fix issues mentioned above

- fix ugly hacks

- implement more stuff (there is a lot of it, and it won't get done if nobody helps... ideally pick a simple-ish application and stub/implement stuff until it works)

- explore using bubblewrap to enforce the security policies that google helpfully forces apps to comply with (and our own security policies, like no internet access for apps which really shouldn't need it and are not scummy enough to refuse to launch without it)

### Tips

- the correct format for changing verbosity of messages going through android's logging library is `ANDROID_LOG_TAGS=*:v` (where `*` is "all tags" and `v` is "verbosity `verbose` or lesser"  
(note that specifying anything other than `*` as the tag will not work with the host version of liblog)