[camerax] Update README with plugin overview

packages/camera/camera_android_camerax/CHANGELOG.md

@@ -21,3 +21,4 @@
 * Implements image streaming.
 * Provides LifecycleOwner implementation for Activities that use the plugin that do not implement it themselves.
 * Implements retrieval of camera information.
+* Updates README with plugin overview.

packages/camera/camera_android_camerax/CONTRIBUTING.md

@@ -0,0 +1,46 @@
+# Contributing to camera\_android\_camerax
+
+## Plugin structure
+
+The `camera_platform_interface` implementation is located at
+`lib/src/android_camera_camerax.dart`, and it is implemented using Dart classes that
+are wrapped versions of native Android Java classes.
+
+In `lib/src/`, you will find all of the Dart-wrapped native classes that the plugin
+currently uses in its implementation. Each of these classes uses an `InstanceManager`
+(implementation in `instance_manager.dart`) to manage objects that are created by
+the plugin implementation that map to objects of the same type created on the native
+side. This plugin uses [`pigeon`][1] to generate the communication layer between Flutter
+and native Android code, so each of these Dart-wrapped classes also have Host API and
+Flutter API implementations, as needed. The communication interface is defined in
+the `pigeons/camerax_library.dart` file. After editing the communication interface,
+regenerate the communication layer by running
+`dart run pigeon --input pigeons/camerax_library.dart` from the plugin root.
+
+On the native side in `android/src/main/java/io/flutter/plugins/camerax/`, you'll
+find the Host API and Flutter API implementations of the same classes wrapped with
+Dart in `lib/src/`. These implementations call directly to the classes that they 
+are wrapping in the CameraX library or other Android libraries. The objects created
+in the native code map to objects created on the Dart side, and thus, are also
+managed by an `InstanceManager` (implementation in `InstanceManager.java`).
+
+If you need to access any Android classes to contribute to this plugin, you should
+search in `lib/src/` for any Dart-wrapped classes you may need. If any classes that
+you need are not wrapped or you need to access any methods not wrapped in a class,
+you must take the additional steps to wrap them to maintain the structure of this plugin.
+
+For more information on the approach of wrapping native libraries for plugins, please
+see the [design document][2]. For more information on contributing packages in general,
+check out our [contribution guide][3].
+
+## Testing
+
+Besides [`pigeon`][1], this plugin also uses [`mockito`][4] to generate mock objects for
+testing purposes. To generate the mock objects, run
+`dart run build_runner build --delete-conflicting-outputs`.
+
+
+[1]: https://pub.dev/packages/pigeon
+[2]: https://docs.google.com/document/d/1wXB1zNzYhd2SxCu1_BK3qmNWRhonTB6qdv4erdtBQqo/edit?usp=sharing&resourcekey=0-WOBqqOKiO9SARnziBg28pg
+[3]: https://github.com/flutter/packages/blob/main/CONTRIBUTING.md
+[4]: https://pub.dev/packages/mockito

packages/camera/camera_android_camerax/README.md

@@ -1,3 +1,64 @@
-# camera_android_camerax
+# camera\_android\_camerax
 
-An implementation of the camera plugin on Android using CameraX.
+An Android implementation of [`camera`][1] that uses the [CameraX library][2].
+
+*Note*: This package is under development.
+See [missing features and limitations](#missing-features-and-limitations).
+
+## Usage
+
+This package is [non-endorsed][3]; the endorsed Android implementation of `camera`
+is [`camera_android`][4]. To use this implementation of the plugin instead of
+`camera_android`, you will need to specify it in your `pubsepc.yaml` file as a
+dependency in addition to `camera`:
+
+```yaml
+dependencies:
+  # ...along with your other dependencies
+  camera: ^0.10.4
+  camera_android_camerax: ^0.5.0
+```
+
+## Missing features and limitations
+
+### Resolution configuration \[[Issue #120462][120462]\]
+
+Any specified `ResolutionPreset` wll go unused in favor of CameraX defaults and
+`onCameraResolutionChanged` is unimplemented.
+
+### Locking/Unlocking capture orientation \[[Issue #125915][125915]\]
+
+`lockCaptureOrientation` & `unLockCaptureOrientation` are unimplemented.
+
+### Flash mode configuration \[[Issue #120715][120715]\]
+
+`setFlashMode` is unimplemented.
+
+### Exposure mode, point, & offset configuration \[[Issue #120468][120468]\]
+
+`setExposureMode`, `setExposurePoint`, & `setExposureOffset` are unimplemented.
+
+### Focus mode & point configuration \[[Issue #120467][120467]\]
+
+`setFocusMode` & `setFocusPoint` are unimplemented.
+
+### Zoom configuration \[[Issue #125371][125371]\]
+
+`setZoomLevel` is unimplemented.
+
+## Contributing
+
+For more information on contributing to this plugin, see [`CONTRIBUTING.md`](CONTRIBUTING.md).
+
+<!-- Links -->
+
+[1]: https://pub.dev/packages/camera
+[2]: https://developer.android.com/training/camerax
+[3]: https://docs.flutter.dev/packages-and-plugins/developing-packages#non-endorsed-federated-plugin
+[4]: https://pub.dev/packages/camera_android
+[120462]: https://github.com/flutter/flutter/issues/120462
+[125915]: https://github.com/flutter/flutter/issues/125915
+[120715]: https://github.com/flutter/flutter/issues/120715
+[120468]: https://github.com/flutter/flutter/issues/120468
+[120467]: https://github.com/flutter/flutter/issues/120467
+[125371]: https://github.com/flutter/flutter/issues/125371