# flutter - 浮水印（使用套件 image ）

| 圖片浮水印 | 文字浮水印 | 滿版浮水印 |
| -------- | -------- | -------- |
| |  | |

## 安裝套件

flutter pub add image

## 程式碼
### 使用方式

//添加 assets 內的圖片浮水印
WaterMark.addImg(
  oriFilePath: file.path,
  waterMarkAssetsPath: 'images/yen.png',
  waterMarkHeight: 100,
  waterMarkWidth: 100
);

//添加浮水印文字
WaterMark.addText(
    oriFilePath: file.path,
    waterMarkText: 'photo by YEN',
);

//添加滿版浮水印
WaterMark.addFullText(
    oriFilePath: file.path,
    waterMarkText: 'photo by YEN',
);

### 小工具

import 'dart:io';
import 'package:flutter/services.dart';
import 'package:image/image.dart';
import 'package:path_provider/path_provider.dart';

class WaterMark {
  static Future<File> addImg({
    required String oriFilePath,
    required String waterMarkAssetsPath,
    required int waterMarkHeight,
    required int waterMarkWidth,
    int bottomPadding = 10,
    int rightPadding = 10,
  }) async {
    File oriFile = File(oriFilePath);
    File waterMarkFile = await _getImageFileFromAssets(waterMarkAssetsPath);
    Uint8List oriUint8List = oriFile.readAsBytesSync();
    Image? oriImg = decodeJpg(oriUint8List);
    Image? waterMarkImg = decodePng(waterMarkFile.readAsBytesSync());

    drawImage(oriImg!, waterMarkImg!,
        dstW: waterMarkWidth,
        dstH: waterMarkHeight,
        dstX: oriImg.width - waterMarkWidth - rightPadding,
        dstY: oriImg.height - waterMarkHeight - bottomPadding);

    return await oriFile.writeAsBytes(encodeJpg(oriImg));
  }

  static Future<Future<File>> addText({
    required String oriFilePath,
    required String waterMarkText,
    int bottomPadding = 10,
    int rightPadding = 10,
  }) async {
    File oriFile = File(oriFilePath);
    Image? oriImg = decodeJpg(oriFile.readAsBytesSync());
    drawString(oriImg!, arial_24, (oriImg.width - rightPadding),
        oriImg.height - bottomPadding - 24, waterMarkText,
        rightJustify: true);
    return oriFile.writeAsBytes(encodeJpg(oriImg));
  }

  static Future<Future<File>> addFullText({
    required String oriFilePath,
    required String waterMarkText,
    int horizontalPadding = 10,
    int verticalPadding = 40,
  }) async {
    File oriFile = File(oriFilePath);
    Image? oriImg = decodeJpg(oriFile.readAsBytesSync());
    int fontSize = 24;

    for (var j = 0, countj = 0; j < oriImg!.height - fontSize * 2; j++) {
      j = j + verticalPadding;
      for (var i = 0, counti = 0;
          i < oriImg.width - horizontalPadding * 2;
          i++) {
        i = i + horizontalPadding;
        if (countj % 2 == 0 && counti % 2 == 0 ||
            countj % 2 == 1 && counti % 2 == 1) {
          drawString(oriImg, arial_24, i, j, waterMarkText, color: 0x80ffffff);
        }
        i = i + waterMarkText.length * ((fontSize / 2).ceil());

        counti = counti + 1;
      }
      j = j + verticalPadding;
      countj = countj + 1;
    }

    return oriFile.writeAsBytes(encodeJpg(oriImg));
  }

  static Future<File> _getImageFileFromAssets(String path) async {
    final byteData = await rootBundle.load('assets/$path');

    final file = File('${(await getTemporaryDirectory()).path}/$path');
    if (!file.existsSync()) {
      await file.create(recursive: true);
    }
    await file.writeAsBytes(byteData.buffer
        .asUint8List(byteData.offsetInBytes, byteData.lengthInBytes));

    return file;
  }
}

###### tags: `flutter`