flutter 图片裁剪

上次做了图片裁剪的需求没有记录, 最近遇到了身份证裁剪的需求又忘记处理方法了,处理完毕后记录一下

需求: 根据形状拍照,并进行裁剪

方案: 拍照。==》裁剪 ==》存储 ==》上传

步骤:

1、将file转化为image

  changeFileWithImage(String filePath) async {

    Uint8List bytes = await file2Uint8List(File(filePath));

    ui.Codec codec = await ui.instantiateImageCodec(bytes,

        targetWidth: screenWidth.toInt(), targetHeight: screenHeight.toInt());

    ui.FrameInfo fi = await codec.getNextFrame();

    return fi.image;

  }

2、构建画布

Paint paint = Paint();

    PictureRecorder recorder = PictureRecorder();

    Canvas canvas2 = Canvas(recorder);

3、根据宽高比 计算实际裁剪宽高

    double whrate = coverHeight / coverWidth;

    double realHeight = screenWidth / whrate;

    double topy = (screenHeight - realHeight) / 2;

3、处理被对照尺寸

    Rect source = Rect.fromLTWH(0, topy, screenWidth, realHeight);

4、处理实际裁剪尺寸

    Rect dest = Rect.fromLTWH(0, 0, screenWidth, realHeight);

    canvas2.drawImageRect(fileImage, source, dest, paint);

5、裁剪

    var image2 = recorder

        .endRecording()

        .toImage(dest.width.toInt(), dest.height.toInt());

    image2.then((value) async {

 6、将图片转化为字节

      ByteData? byteData = await value.toByteData(format: ImageByteFormat.png);

      Uint8List pngBytes = byteData!.buffer.asUint8List();

7、存储图片文件文件

      new File(filePath).writeAsBytesSync(pngBytes);

      idCardPath = filePath;

      completer.complete();