mob_camera

# mob_camera

Native camera capture, live preview, and frame streaming for apps built with
[Mob](https://hexdocs.pm/mob) — `Mob.Camera`, extracted from mob core as a plugin.

iOS: `UIImagePickerController` + a shared `AVCaptureSession` (vImage frame
conversion). Android: `TakePicture`/`CaptureVideo` activity contracts.

## Platform support

| Feature | iOS | Android |
|---|---|---|
| `capture_photo/2`, `capture_video/2` | ✅ | ✅ |
| `start_preview/2` + `Mob.UI.camera_preview/1` | ✅ live feed | ⏳ accepted, renders nothing |
| `start_frame_stream/2` | ✅ delivers frames | ⏳ accepted, delivers nothing |

Capture works fully on both platforms today. Live preview and frame streaming
are **iOS-only** for now — on Android, `start_preview/2` and
`start_frame_stream/2` return successfully and track state, but nothing binds
a CameraX `ImageAnalysis`/`Preview` use case to that state, so no frame is
ever delivered and the preview view stays blank. No error is raised; see
[Limits](#limits) for why and what's blocking it.

## Installation

```elixir
# mix.exs
{:mob_camera, "~> 0.1"}

# mob.exs
config :mob, :plugins, [:mob_camera]
```

The plugin manifest merges `NSCameraUsageDescription` (iOS) and `CAMERA` /
`RECORD_AUDIO` (Android) into the host app at build time, and registers the
`:camera` permission capability — request it via
`Mob.Permissions.request(socket, :camera)` before capturing. (`:microphone`,
needed for video, stays in core.)

## Usage

```elixir
socket = MobCamera.capture_photo(socket, quality: :high)
socket = MobCamera.capture_video(socket, max_duration: 60)

def handle_info({:camera, :photo, %{path: path, width: w, height: h}}, socket), do: ...
def handle_info({:camera, :video, %{path: path, duration: seconds}}, socket), do: ...
def handle_info({:camera, :cancelled}, socket), do: ...
```

`path` is a local temp file — copy it elsewhere before the next capture.

For real-time work (object detection, AR, custom filters), stream frames
(**iOS only** — see [Platform support](#platform-support)):

```elixir
socket = MobCamera.start_frame_stream(socket, width: 640, height: 640, format: :rgb_f32)

def handle_info({:camera, :frame, %{bytes: bin, width: w, height: h,
                                    format: :rgb_f32, timestamp_ms: _t,
                                    dropped: _n}}, socket) do
  # :rgb_f32 is Nx-ready: Nx.from_binary(bin, :f32) |> Nx.reshape({1, h, w, 3})
end
```

Resize + format conversion happen natively, and late frames are dropped
natively, so the BEAM mailbox stays bounded. Other options: `format: :bgra_u8`,
`facing: :front`, `throttle_ms:`. Stop with `MobCamera.stop_frame_stream/1`.

Live preview pairs a session from this plugin with a view component from core
(**iOS only** — see [Platform support](#platform-support)):

```elixir
socket = MobCamera.start_preview(socket, facing: :back)
# in render/1:
{Mob.UI.camera_preview(facing: :back)}
```

## Host app requirements

Photo/video capture saves through a FileProvider: `AndroidManifest.xml` must
declare an `androidx.core.content.FileProvider` `<provider>` with
`res/xml/file_provider_paths.xml`. mob_new-generated apps include it;
hand-rolled hosts must add it or capture returns `:cancelled`.

## Limits

- **Android live preview and frame streaming are not implemented — only
  state tracking is.** `camera_start_preview`/`camera_start_frame_stream` in
  `MobCameraBridge.kt` set fields and bump a revision counter; nothing binds
  a CameraX `Preview`/`ImageAnalysis` use case to the capture session, so
  `deliverFrame` (which would forward pixel data to the BEAM) is never
  called. `start_preview/2` and `start_frame_stream/2` both return
  successfully — there is no error, the calls just have no effect on
  Android. Capture (`capture_photo/2`, `capture_video/2`) is unaffected and
  fully implemented on both platforms.
- The preview *view* node (`Mob.UI.camera_preview/1`) stays in mob core for
  now — this plugin owns the session (`start_preview/2` / `stop_preview/1`).
  Moving the view here, and wiring the Android CameraX binding above, both
  wait on the plugin native-view capability.
- Frame size is capped at ~4 MP; mismatched aspect ratios are center-cropped
  on the long axis before scaling. (iOS only — see above.)

## Development

Clone, then run once:

```bash
mix setup
```

That fetches deps and activates the repo's git hooks (`.githooks/pre-push`):
`mix format --check`, `mix credo --strict` (incl. ExSlop), and `mix compile --warnings-as-errors` run on every push, plus the full test
suite when `mix.exs` changes — the same gate CI enforces before publishing.

## License

MIT