Flutter轻量级相机功能插件flutter_lite_camera的使用

Flutter Lite Camera 是一个专为在 Windows、Linux 和 macOS 平台上以固定分辨率为 640x480 捕获 RGB888 格式帧的轻量级 Flutter 插件。该插件非常适合用于构建相机预览应用和进行图像处理任务。

特性

• 跨平台：兼容 Windows、Linux 和 macOS。
• RGB888 帧格式：捕获未压缩的 RGB888 帧，便于图像处理。
• 简单集成：提供易于使用的 API，方便与 Flutter 集成。

要求

• Flutter SDK: 版本 3.0.0 或以上
• 权限: 在 macOS 上确保授予相机访问权限。在 DebugProfile.entitlements 或 Release.entitlements 中添加：

  <key>com.apple.security.device.camera</key>
  <true/>
  

API

示例代码

import 'package:flutter/material.dart';
import 'dart:async';

import 'package:flutter/services.dart';
import 'package:flutter_lite_camera/flutter_lite_camera.dart';
import 'dart:ui' as ui;

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  [@override](/user/override)
  Widget build(BuildContext context) {
    return MaterialApp(
      home: CameraApp(),
    );
  }
}

class CameraApp extends StatefulWidget {
  [@override](/user/override)
  State<CameraApp> createState() => _CameraAppState();
}

class _CameraAppState extends State<CameraApp> {
  final FlutterLiteCamera _flutterLiteCameraPlugin = FlutterLiteCamera();
  bool _isCameraOpened = false;
  bool _isCapturing = false;
  int _width = 640;
  int _height = 480;
  ui.Image? _latestFrame;
  bool _shouldCapture = false;

  [@override](/user/override)
  void initState() {
    super.initState();
    _handleWindowClose();
  }

  Future<void> _startCamera() async {
    try {
      List<String> devices = await _flutterLiteCameraPlugin.getDeviceList();
      if (devices.isNotEmpty) {
        print("Available Devices: $devices");
        print("Opening camera 0");
        bool opened = await _flutterLiteCameraPlugin.open(0);
        if (opened) {
          setState(() {
            _isCameraOpened = true;
            _shouldCapture = true;
          });

          // 开始捕获帧
          _isCapturing = true;
          _captureFrames();
        } else {
          print("Failed to open the camera.");
        }
      }
    } catch (e) {
      // print("Error initializing camera: $e");
    }
  }

  Future<void> _captureFrames() async {
    if (!_isCameraOpened || !_shouldCapture) return;

    try {
      Map<String, dynamic> frame = await _flutterLiteCameraPlugin.captureFrame();
      if (frame.containsKey('data')) {
        Uint8List rgbBuffer = frame['data'];
        await _convertBufferToImage(rgbBuffer, frame['width'], frame['height']);
      }
    } catch (e) {
      // print("Error capturing frame: $e");
    }

    // 安排下一次帧捕获
    if (_shouldCapture) {
      Future.delayed(const Duration(milliseconds: 30), _captureFrames);
    }
  }

  Future<void> _convertBufferToImage(Uint8List rgbBuffer, int width, int height) async {
    final pixels = Uint8List(width * height * 4); // RGBA 缓冲区

    for (int i = 0; i < width * height; i++) {
      int r = rgbBuffer[i * 3];
      int g = rgbBuffer[i * 3 + 1];
      int b = rgbBuffer[i * 3 + 2];

      // 填充 RGBA 缓冲区
      pixels[i * 4] = b;
      pixels[i * 4 + 1] = g;
      pixels[i * 4 + 2] = r;
      pixels[i * 4 + 3] = 255; // Alpha 通道
    }

    final completer = Completer<ui.Image>();
    ui.decodeImageFromPixels(
      pixels,
      width,
      height,
      ui.PixelFormat.rgba8888,
      completer.complete,
    );

    final image = await completer.future;
    setState(() {
      _latestFrame = image;
    });
  }

  Future<void> _stopCamera() async {
    setState(() {
      _shouldCapture = false;
    });

    if (_isCameraOpened) {
      await _flutterLiteCameraPlugin.release();
      setState(() {
        _isCameraOpened = false;
        _latestFrame = null;
      });
    }

    _isCapturing = false;
  }

  void _handleWindowClose() {
    WidgetsBinding.instance.addPostFrameCallback((_) {
      SystemChannels.lifecycle.setMessageHandler((message) async {
        if (message == AppLifecycleState.detached.toString()) {
          await _stopCamera();
        }
        return null;
      });
    });
  }

  [@override](/user/override)
  void dispose() {
    _stopCamera();
    super.dispose();
  }

  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: [
          if (_latestFrame != null)
            LayoutBuilder(
              builder: (context, constraints) {
                final screenWidth = constraints.maxWidth;
                final screenHeight = constraints.maxHeight;
                final imageAspectRatio = _width / _height;
                final screenAspectRatio = screenWidth / screenHeight;

                double drawWidth, drawHeight;
                if (imageAspectRatio > screenAspectRatio) {
                  drawWidth = screenWidth;
                  drawHeight = screenWidth / imageAspectRatio;
                } else {
                  drawHeight = screenHeight;
                  drawWidth = screenHeight * imageAspectRatio;
                }

                return Center(
                  child: CustomPaint(
                    painter: FramePainter(_latestFrame!),
                    child: SizedBox(
                      width: drawWidth,
                      height: drawHeight,
                    ),
                  ),
                );
              },
            )
          else
            Center(
              child: Text('Camera not initialized or no frame captured'),
            ),
          Positioned(
            bottom: 20,
            left: 20,
            right: 20,
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                // 开始按钮
                ElevatedButton(
                  onPressed: _isCapturing ? null : () => _startCamera(),
                  child: const Text('Start'),
                ),
                // 停止按钮
                ElevatedButton(
                  onPressed: !_isCapturing ? null : () => _stopCamera(),
                  child: const Text('Stop'),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}

class FramePainter extends CustomPainter {
  final ui.Image image;

  FramePainter(this.image);

  [@override](/user/override)
  void paint(Canvas canvas, Size size) {
    final paint = Paint();
    canvas.drawImageRect(
      image,
      Rect.fromLTWH(0, 0, image.width.toDouble(), image.height.toDouble()),
      Rect.fromLTWH(0, 0, size.width, size.height),
      paint,
    );
  }

  [@override](/user/override)
  bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}