之前一篇给图片加水印的功能，加出来水印的图片位置有一点问题，并且如果图片分辨率有变动的话，水印会有层次不齐的问题。
目前只能优化到增加一条居中显示的斜水印，在不同分辨率不同大小的图片中，都能保证文字水印的字体大小从左下至右上能撑满整张图片。
思路是：先生成一张文字水印图片的PNG图片。
在你需要添加水印的图片上，把之前加的水印图片贴上去就可以了。
核心代码：
1 //新建原始普通大小的bmp 2 Bitmap bmCanvas = new Bitmap(imgSrc.Width, imgSrc.Height, PixelFormat.Format24bppRgb); 3 Graphics gCanvas = Graphics.FromImage(bmCanvas); 4 gCanvas.Clear(Color.White); 5 gCanvas.SmoothingMode = SmoothingMode.HighQuality; 6 gCanvas.InterpolationMode = InterpolationMode.High; 7 //将原始图片加载入画布 8 gCanvas.DrawImage(imgSrc, 0, 0, imgSrc.Width, imgSrc.Height); 9 //计算图片对角线长度 10 double diagonal = Math.Sqrt(Math.Pow(width, 2) + Math.Pow(height, 2)); 11 12 //计算对角线倾角 13 double angle = Math.Asin(height / Math.Sqrt(Math.Pow(width, 2) + Math.Pow(height, 2))) / Math.PI * 180; 14 15 // 确定水印文字的字体大小 16 int[] sizes = new int[] 17 { 18 280, 276, 272, 268, 264, 260, 256, 252, 248, 244, 240, 236, 232, 228, 224, 220, 216, 212, 208, 19 204, 200, 196, 192, 188, 184, 180, 176, 172, 168, 164, 160, 156, 152, 148, 144, 140, 136, 132, 20 128, 124, 120, 116, 112, 108, 104, 100, 96, 92, 88, 84, 80, 76, 72, 68, 64, 60, 56, 52, 48, 44, 21 40, 36, 32, 28, 24, 20, 16, 12, 8, 4 22 }; 23 Font crFont = null; 24 SizeF crSize = new SizeF(); 25 26 for (int i = 0; i < sizes.Length; i++) 27 { 28 crFont = new Font("微软雅黑", sizes[i], FontStyle.Bold); 29 crSize = gCanvas.MeasureString(watermarkText, crFont); 30 if ((int)crSize.Width < (int)diagonal * 0.9) 31 { 32 break; 33 } 34 } 35 // 生成水印图片（将文字写到图片中） 36 //Bitmap bmWaterMark = new Bitmap((int)crSize.Width + 3, (int)crSize.Height + 3, PixelFormat.Format32bppArgb); 37 Bitmap bmWaterMark = new Bitmap(width, height, PixelFormat.Format32bppArgb); 38 Graphics gWaterMark = Graphics.FromImage(bmWaterMark); 39 40 gWaterMark.TranslateTransform(width / 2, height / 2); 41 gWaterMark.RotateTransform(-(int)angle); 42 gWaterMark.TranslateTransform(-crSize.Width / 2, -crSize.Height / 2); 43 44 PointF pt = new PointF(0, 0); 45 // 画阴影文字 46 Brush transparentBrush0 = new SolidBrush(Color.FromArgb(255, Color.Black)); 47 Brush transparentBrush1 = new SolidBrush(Color.FromArgb(255, Color.Black)); 48 gWaterMark.DrawString(watermarkText, crFont, transparentBrush0, pt.X, pt.Y + 1); 49 gWaterMark.DrawString(watermarkText, crFont, transparentBrush0, pt.X + 1, pt.Y); 50 gWaterMark.DrawString(watermarkText, crFont, transparentBrush1, pt.X + 1, pt.Y + 1); 51 gWaterMark.DrawString(watermarkText, crFont, transparentBrush1, pt.X, pt.Y + 2); 52 gWaterMark.DrawString(watermarkText, crFont, transparentBrush1, pt.X + 2, pt.Y); 53 transparentBrush0.Dispose(); 54 transparentBrush1.Dispose(); 55 56 // 画文字 57 gWaterMark.SmoothingMode = SmoothingMode.HighQuality; 58 //Brush SolidBrush3 = new SolidBrush(Color.White); 59 Brush solidBrush3 = new SolidBrush(Color.FromArgb(255, Color.White)); 60 gWaterMark.DrawString(watermarkText, crFont, solidBrush3, pt.X, pt.Y, StringFormat.GenericDefault); 61 solidBrush3.Dispose(); 62 63 // 保存刚才的操作 64 gWaterMark.Save(); 65 gWaterMark.Dispose(); 66 bmWaterMark.Save(_wmImgSavePath, ImageFormat.Jpeg); 67 68 //// 将水印图片加到原图中 69 //AddWatermarkImage(gCanvas, new Bitmap(bmWaterMark), "WM_TOP_LEFT", width, height); 70 71 using (var imageAttr = new ImageAttributes()) 72 { 73 ColorMap colorMap = new ColorMap(); 74 colorMap.OldColor = Color.FromArgb(255, 0, 255, 0); 75 colorMap.NewColor = Color.FromArgb(0, 0, 0, 0); 76 ColorMap[] remapTable = { colorMap }; 77 imageAttr.SetRemapTable(remapTable, ColorAdjustType.Bitmap); 78 float[][] colorMatrixElements = 79 { 80 new float[] {1.0f, 0.0f, 0.0f, 0.0f, 0.0f}, 81 new float[] {0.0f, 1.0f, 0.0f, 0.0f, 0.0f}, 82 new float[] {0.0f, 0.0f, 1.0f, 0.0f, 0.0f}, 83 new float[] {0.0f, 0.0f, 0.0f, 0.3f, 0.0f}, 84 new float[] {0.0f, 0.0f, 0.0f, 0.0f, 1.0f} 85 }; 86 ColorMatrix colorMatrix = new ColorMatrix(colorMatrixElements); 87 imageAttr.SetColorMatrix(colorMatrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap); 88 gCanvas.DrawImage(bmWaterMark, new Rectangle(10, 10, bmWaterMark.Width, bmWaterMark.Height), 0, 0, 89 bmWaterMark.Width, bmWaterMark.Height, GraphicsUnit.Pixel, imageAttr); 90 gCanvas.Dispose(); 91 } 92 bmWaterMark.Dispose();
代码已上传至GitHub，地址：https://github.com/hano7758/WaterMark