CSharp基于开源项目SkiaSharp实现图片压缩与加水印

1、首先命令行安装插件

Install-Package SkiaSharp

2、基于图片质量的压缩

       /// <summary>
        /// 压缩图片
        /// </summary>
        /// <param name="source"> 原文件位置 </param>
        /// <param name="target"> 生成目标文件位置</param>
        /// <param name="scale">  图片缩放比例：大于1放大；小于1,[0-1]缩小</param>
        /// <param name="quality">图片质量，范围0-100</param>
        public static void Compress(string source, string target, decimal scale, int quality)
        {
              using (var file = File.OpenRead(source))
              using (var fileStream = new SKManagedStream(file))
              using (var bitmap = SKBitmap.Decode(fileStream))
              {
                    var width = (decimal)bitmap.Width;
                    var height = (decimal)bitmap.Height;

                    var maxWidth = bitmap.Width*scale;
                    var newWidth = maxWidth;
                    var newHeight = height / width * maxWidth;

                    using (var resized = bitmap.Resize(new SKImageInfo((int) newWidth, (int) newHeight), SKFilterQuality.Medium))
                    { 
                          using (var image = SKImage.FromBitmap(resized))
                          using (var writeStream = File.OpenWrite(target))
                          {
                              image.Encode(GetFormat(target), quality).SaveTo(writeStream);
                          } 
                    }
              }
        }

其中，GetFormat 方法：

private static SKEncodedImageFormat GetFormat(string file)
 {
            var ext= Path.GetExtension(file).TrimStart('.').ToLower();
            SKEncodedImageFormat format= SKEncodedImageFormat.Png;
            switch (ext)
            {
                case "jpg":
                case "jpeg":
                    format = SKEncodedImageFormat.Jpeg;
                    break;
                case "png":
                    format = SKEncodedImageFormat.Png;
                    break;
                case "gif":
                    format = SKEncodedImageFormat.Gif;
                    break;
                case "webp":
                    format = SKEncodedImageFormat.Webp;
                    break;
                case "wbmp":
                    format = SKEncodedImageFormat.Wbmp;
                    break;
                case "bmp":
                    format = SKEncodedImageFormat.Bmp;
                    break;
                case "astc":
                    format = SKEncodedImageFormat.Astc;
                    break;
                case "dng":
                    format = SKEncodedImageFormat.Dng;
                    break;
                default:
                    format = SKEncodedImageFormat.Avif;
                    break;
            }
            return format;
 }

3、图片加水印

可以先定义一组描述添加水印行为的类

public record Margin(int t, int l, int r, int b);

public record MarkerFont(string font, float size, SKColor color,bool fw=true);

public record WaterMarker(string txt, MarkerFont font, Margin m);

然后将通过参数传递，添加水印

public  static  void AddWaterMarkers(string source, string target, List<WaterMarker> markers, int quality = 100)
   {
            using (var file = File.OpenRead(path: source))
            using (var fileStream = new SKManagedStream(file))
            using (var bitmap = SKBitmap.Decode(fileStream))
            {
                var width = (decimal)bitmap.Width;
                var height = (decimal)bitmap.Height;

                //加水印：
                if (markers != null)
                {
                    using (var canvas = new SKCanvas(bitmap))
                    using (SKPaint sKPaint = new SKPaint())
                    {
                        foreach (var marker in markers)
                        {
                            sKPaint.Color = marker.font.color;//字体颜色
                            sKPaint.TextSize = marker.font.size;//字体大小
                            sKPaint.FakeBoldText = true;
                            sKPaint.IsAntialias = true;//开启抗锯齿
                            sKPaint.Typeface = SkiaSharp.SKTypeface.FromFamilyName(marker.font.font ?? "微软雅黑");//字体
                            SKRect size = new SKRect();
                            sKPaint.MeasureText(marker.txt, ref size);//计算文字宽度以及高度

                            float x=0,y=0;
                            if (marker.m.b > 0)
                            {
                                y = (float) (height - marker.m.b - (decimal) size.Height);
                            }
                            else
                            {
                                y = marker.m.t;
                            }
                          
                            if (marker.m.r > 0)
                            {
                                x = (float) (width - marker.m.r - (decimal) size.Width);
                            }
                            else
                            {
                                x = marker.m.l;
                            }
                          
                            canvas.DrawText(marker.txt, x, y, sKPaint);//画文字
                        }

                    }

                }

                using (var writeStream = File.OpenWrite(target))
                {
                    bitmap.Encode(GetFormat(target), quality).SaveTo(writeStream);
                }

         }
}