C#动态生成水印图片的类

1、可以指定文字字体、大小和颜色（注:指定的文字在WEB服务器上需要有该字库）；
2、可以加文字阴影；
3、可以指定文字的透明度；
4、可以指定背景图片或背景颜色；
5、可以指定生成的图片大小（宽度与高度）；
6、可以指定文字的位置（左边距和上边距）；
7、当用户设定的文字字号太大，能自动调整文字大小使之能适应生成图片的大小。

    using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
namespace Ycweb.Controls.Utility
{
	 /**/
	 /// <summary>
	 /// WaterMark
	 /// </summary>
	 public class Watermark
	 {
		  private int _width;
		  private int _height;
		  private string _fontFamily;
		  private int _fontSize;
		  private bool _adaptable;
		  private FontStyle _fontStyle;
		  private bool _shadow;
		  private string _backgroundImage;
		  private Color _bgColor;
		  private int _left;
		  private string _resultImage;
		  private string _text;
		  private int _top;
		  private int _alpha;
		  private int _red;
		  private int _green;
		  private int _blue;
		  private long _quality;
		  public Watermark()
		  {
				//
				// TODO: Add constructor logic here
				//
				_width = 460;
				_height = 30;
				_fontFamily = "华文行楷";
				_fontSize = 20;
				_fontStyle = FontStyle.Regular;
				_adaptable = true;
				_shadow = false;
				_left = 0;
				_top = 0;
				_alpha = 255;
				_red = 0;
				_green = 0;
				_blue = 0;
				_backgroundImage = "";
				_quality = 100;
				_bgColor = Color.FromArgb(255, 229, 229, 229);
		  }
		  /**/
		  /// <summary>
		  /// 字体
		  /// </summary>
		  public string FontFamily
		  {
				set { this._fontFamily = value; }
		  }
		  /**/
		  /// <summary>
		  /// 文字大小
		  /// </summary>
		  public int FontSize
		  {
				set { this._fontSize = value; }
		  }
		  /**/
		  /// <summary>
		  /// 文字风格
		  /// </summary>
		  public FontStyle FontStyle
		  {
				get { return _fontStyle; }
				set { _fontStyle = value; }
		  }
		  /**/
		  /// <summary>
		  /// 透明度0-255,255表示不透明
		  /// </summary>
		  public int Alpha
		  {
				get { return _alpha; }
				set { _alpha = value; }
		  }
		  /**/
		  /// <summary>
		  /// 水印文字是否使用阴影
		  /// </summary>
		  public bool Shadow
		  {
				get { return _shadow; }
				set { _shadow = value; }
		  }
		  public int Red
		  {
				get { return _red; }
				set { _red = value; }
		  }
		  public int Green
		  {
				get { return _green; }
				set { _green = value; }
		  }
		  public int Blue
		  {
				get { return _blue; }
				set { _blue = value; }
		  }
		  /**/
		  /// <summary>
		  /// 底图
		  /// </summary>
		  public string BackgroundImage
		  {
				set { this._backgroundImage = value; }
		  }
		  /**/
		  /// <summary>
		  /// 水印文字的左边距
		  /// </summary>
		  public int Left
		  {
				set { this._left = value; }
		  }
		  /**/
		  /// <summary>
		  /// 水印文字的顶边距
		  /// </summary>
		  public int Top
		  {
				set { this._top = value; }
		  }
		  /**/
		  /// <summary>
		  /// 生成后的图片
		  /// </summary>
		  public string ResultImage
		  {
				set { this._resultImage = value; }
		  }
		  /**/
		  /// <summary>
		  /// 水印文本
		  /// </summary>
		  public string Text
		  {
				set { this._text = value; }
		  }
		  /**/
		  /// <summary>
		  /// 生成图片的宽度
		  /// </summary>
		  public int Width
		  {
				get { return _width; }
				set { _width = value; }
		  }
		  /**/
		  /// <summary>
		  /// 生成图片的高度
		  /// </summary>
		  public int Height
		  {
				get { return _height; }
				set { _height = value; }
		  }
		  /**/
		  /// <summary>
		  /// 若文字太大，是否根据背景图来调整文字大小，默认为适应
		  /// </summary>
		  public bool Adaptable
		  {
				get { return _adaptable; }
				set { _adaptable = value; }
		  }
		  public Color BgColor
		  {
				get { return _bgColor; }
				set { _bgColor = value; }
		  }
		  /**/
		  /// <summary>
		  /// 输出图片质量，质量范围0-100,类型为long
		  /// </summary>
		  public long Quality
		  {
				get { return _quality; }
				set { _quality = value; }
		  }
		  /**/
		  /// <summary>
		  /// 立即生成水印效果图
		  /// </summary>
		  /// <returns>生成成功返回true,否则返回false</returns>
		  public bool Create()
		  {
				try
				{
					 Bitmap bitmap;
					 Graphics g;
					 //使用纯背景色
					 if (this._backgroundImage.Trim() == "")
					 {
						  bitmap = new Bitmap(this._width, this._height, PixelFormat.Format64bppArgb);
						  g = Graphics.FromImage(bitmap);
						  g.Clear(this._bgColor);
					 }
					 else
					 {
						  bitmap = new Bitmap(Image.FromFile(this._backgroundImage));
						  g = Graphics.FromImage(bitmap);
					 }
					 g.SmoothingMode = SmoothingMode.HighQuality;
					 g.InterpolationMode = InterpolationMode.HighQualityBicubic;
					 g.CompositingQuality = CompositingQuality.HighQuality;
					 Font f = new Font(_fontFamily, _fontSize, _fontStyle);
					 SizeF size = g.MeasureString(_text, f);
					 // 调整文字大小直到能适应图片尺寸
					 while (_adaptable == true && size.Width > bitmap.Width)
					 {
						  _fontSize--;
						  f = new Font(_fontFamily, _fontSize, _fontStyle);
						  size = g.MeasureString(_text, f);
					 }
					 Brush b = new SolidBrush(Color.FromArgb(_alpha, _red, _green, _blue));
					 StringFormat StrFormat = new StringFormat();
					 StrFormat.Alignment = StringAlignment.Near;
					 if (this._shadow)
					 {
						  Brush b2 = new SolidBrush(Color.FromArgb(90, 0, 0, 0));
						  g.DrawString(_text, f, b2, _left + 2, _top + 1);
					 }
					 g.DrawString(_text, f, b, new PointF(_left, _top), StrFormat);
					 bitmap.Save(this._resultImage, ImageFormat.Jpeg);
					 bitmap.Dispose();
					 g.Dispose();
					 return true;
				}
				catch
				{
					 return false;
				}
		  }
	 }
}