dual_capture

Capture back and front camera in one tap. The two shots are composited into a single JPEG with a picture-in-picture overlay — you get the composited image plus both raw files.

Features

• One-call API: DualCapture.capture(context)
• Back → front sequential pipeline with automatic camera switching
• Picture-in-picture overlay at any corner (bottom-right, bottom-left, top-right, top-left)
• Configurable overlay size, margin, JPEG quality, and front-camera flip
• Optional rounded-corner border around the overlay
• Compositing runs in a background isolate (no UI jank)
• Embedded preview support via DualCaptureController + DualCapturePreview

Platform setup

iOS

Add the following entries to ios/Runner/Info.plist:

<key>NSCameraUsageDescription</key>
<string>dual_capture needs camera access to take photos.</string>

Android

Add to android/app/src/main/AndroidManifest.xml inside <manifest>:

<uses-permission android:name="android.permission.CAMERA" />

Getting started

dependencies:
  dual_capture: ^0.1.0

Usage

One-shot capture

import 'package:dual_capture/dual_capture.dart';

final result = await DualCapture.capture(context);
if (result != null) {
  // result.compositedFile  — back + front composited JPEG
  // result.backCameraFile  — raw back-camera JPEG
  // result.frontCameraFile — raw front-camera JPEG
  // result.capturedAt      — UTC DateTime
}

Custom options

final result = await DualCapture.capture(
  context,
  options: const DualCaptureOptions(
    overlayPosition: OverlayPosition.topLeft,
    overlayScale: 0.25,
    jpegQuality: 90,
    overlayBorder: OverlayBorder(
      color: Color(0xFF6C63FF),
      width: 3.0,
      cornerRadius: 16.0,
    ),
  ),
);

Embedded preview (controller API)

class _MyState extends State<MyPage> {
  late final DualCaptureController _ctrl;

  @override
  void initState() {
    super.initState();
    _ctrl = DualCaptureController();
    _ctrl.initialize();
  }

  @override
  void dispose() {
    _ctrl.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Expanded(child: DualCapturePreview(controller: _ctrl)),
        ElevatedButton(
          onPressed: _ctrl.state == DualCaptureState.readyBack
              ? () async {
                  final result = await _ctrl.capture();
                  // use result …
                }
              : null,
          child: const Text('Capture'),
        ),
      ],
    );
  }
}

API

Class / member	Description
DualCapture.capture(context, {options})	Pushes capture UI, returns DualCaptureResult?
DualCaptureController	Manages the pipeline; extends ChangeNotifier
DualCaptureController.initialize()	Opens back camera
DualCaptureController.capture()	Runs full pipeline, returns result
DualCaptureController.state	Current DualCaptureState
DualCapturePreview	Widget that shows the live camera feed
DualCaptureScreen	Full-screen camera UI (used internally by DualCapture.capture)
DualCaptureOptions	All capture settings in one object
DualCaptureResult	Holds the three output files + timestamp
OverlayPosition	Enum: bottomRight, bottomLeft, topRight, topLeft
OverlayBorder	Optional border around the PiP overlay
DualCaptureException	Thrown when the pipeline encounters an error

How it works

┌─────────────────────────────────────────────────────┐
│ 1. Open back camera → show preview                  │
│ 2. User taps shutter → takePicture() (back)         │
│ 3. Dispose back controller (iOS race-condition fix) │
│ 4. Open front camera → warm-up delay → takePicture()│
│ 5. Dispose front controller                         │
│ 6. Background isolate:                              │
│    a. Decode both JPEGs                             │
│    b. Resize front to overlayScale × back width     │
│    c. Optionally flip front horizontally            │
│    d. Apply rounded corners + optional border       │
│    e. Composite onto back image at chosen corner    │
│    f. Encode result as JPEG                         │
│ 7. Return DualCaptureResult                         │
└─────────────────────────────────────────────────────┘

Contributing

PRs and issues welcome at the issue tracker.