近期项目中有给上传的图片添加水印功能，如下图所示

图片添加水印.jpg

水印图片如下

add.png

项目中用到的是的水印覆盖到全部图片的效果，对水印图片进行尺寸压缩，压缩成和上传图片一样的大小。如果需要添加的是固定大小的水印，则不必压缩。

public class WaterImageTools { 

    static int compressH;
    static int compressW;
    public static String createWaterMaskImage(Context context, String filePath) {

        calcuateCompressSize(filePath);
        //将要上传的图片转化为bitmap并压缩
        Bitmap bitmap = BitmapFactory.decodeFile(filePath);
        final Bitmap comBit = Bitmap.createScaledBitmap(bitmap, compressW, compressH, true);

        //将水印压缩成和上传图片一样大小
        Bitmap watermark = BitmapFactory.decodeResource(context.getResources(), R.mipmap.water);
        final Bitmap comWatermark = Bitmap.createScaledBitmap(watermark, compressW, compressH, true);

        if (comBit == null) {
            return null;
        }

        int w = comBit.getWidth();
        int h = comBit.getHeight();

        final Bitmap newb = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);// 创建一个新的和SRC长度宽度一样的位图

        final Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                Canvas cv = new Canvas(newb);
                cv.drawBitmap(comBit, 0, 0, null);// 在 0，0坐标开始画入src
                cv.drawBitmap(comWatermark, 0, 0, null);// 在0，0坐标画入水印，可根据需求自行设置
                cv.save(Canvas.ALL_SAVE_FLAG);// 保存
                cv.restore();// 存储

            }
        });
        thread.start();

        //将添加水印的bitmap转化为file并获取文件路径
        return saveMyBitmap(newb).getAbsolutePath();
    }

    public static File saveMyBitmap(Bitmap mBitmap) {
        File storageDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM);
        File file = null;
        try {
            file = File.createTempFile(
                    UploadAccess.generateFileName(),  /* prefix */
                    ".jpg",         /* suffix */
                    storageDir      /* directory */
            );

            FileOutputStream out = new FileOutputStream(file);
            mBitmap.compress(Bitmap.CompressFormat.JPEG, 20, out);
            out.flush();
            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return file;
    }
    //计算图片压缩尺寸，按宽高比进行压缩
    private static void calcuateCompressSize(String filePath) {
        Bitmap bitmap = BitmapFactory.decodeFile(filePath);
        float h = bitmap.getHeight();
        float w = bitmap.getWidth();
        float expactH = 1920;
        float expactW = 1080;
        float ratioH;
        float ratioW;
       

        if (h < expactH && w < expactW){
          compressH = (int) h;
          compressW = (int) w;
        }else {
            ratioH = h/expactH;
            ratioW = w/expactW;
            if (ratioH > ratioW){
                compressH = (int) expactH;
                compressW = (int) (w / ratioH);
            }else {
                compressW = (int) expactW;
                compressH = (int) (h / ratioW);
            }

        }
    }
}