1 public class Watermark   2 {   3     private string text;   4     private int gap;   5     private Font font = new Font("微软雅黑", 16, FontStyle.Regular);   6     private Color color = Color.FromArgb(255, 0, 0, 0);   7    8     private Form form = new Form();   9   10     public Watermark(Form ownerForm, string text = "Watermark", int gap = 75, double opacity = 0.1, Font font = null, Color? color = null)  11     {  12         this.text = text;  13         this.gap = gap;  14         if (font != null)  15         {  16             this.font = font;  17         }  18         if (color.HasValue)  19         {  20             this.color = color.Value;  21         }  22         form.Size = ownerForm.Size;  23         ownerForm.SizeChanged += OwnerForm_SizeChanged;  24         ownerForm.Move += OwnerForm_Move;  25   26         form.Owner = ownerForm;  27         form.FormBorderStyle = FormBorderStyle.None;  28         form.Opacity = opacity;  29         form.ShowInTaskbar = false;  30         form.TransparencyKey = Color.White;  31         form.BackColor = Color.White;  32   33         form.Paint += Form_Paint;  34         form.Show();  35   36   37         GetWindowLong(form.Handle, GWL_EXSTYLE);  38         SetWindowLong(form.Handle, GWL_EXSTYLE, WS_EX_TRANSPARENT | WS_EX_LAYERED);  39     }  40   41     private void OwnerForm_Move(object sender, EventArgs e)  42     {  43         form.Location = ((Form)sender).Location;  44     }  45   46     private void OwnerForm_SizeChanged(object sender, EventArgs e)  47     {  48         form.Size = ((Form)sender).Size;  49     }  50     private void Form_Paint(object sender, PaintEventArgs e)  51     {  52         const float cos30 = 0.866f;  53         const float sin30 = 0.5f;  54         var g = e.Graphics;  55         g.SmoothingMode = SmoothingMode.AntiAlias;  56         g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;  57         //平移画布到需要画印章的位置  58         g.TranslateTransform(0, gap);  59         //逆时针旋转30度  60         g.RotateTransform(-30);  61         // 绘制画布区域  62         //g.FillRectangle(new SolidBrush(Color.FromArgb(50, 100, 100, 100)), 0, 0, frm.Width, frm.Height);  63         for (int x = 5; x < e.ClipRectangle.Right + gap; x += gap * 2)  64         {  65             for (int y = 5; y < e.ClipRectangle.Bottom + gap; y += gap * 2)  66             {  67                 // 计算文字起点位置  68                 float x1 = cos30 * x - sin30 * y;  69                 float y1 = sin30 * x + cos30 * y;  70                 //画上文字  71                 g.DrawString(text, font, new SolidBrush(color), x1, y1);  72             }  73         }  74     }  75   76     #region 在窗口结构中为指定的窗口设置信息  77     /// <summary>  78     /// 在窗口结构中为指定的窗口设置信息  79     /// </summary>  80     /// <param name="hwnd">欲为其取得信息的窗口的句柄</param>  81     /// <param name="nIndex">欲取回的信息</param>  82     /// <param name="dwNewLong">由nIndex指定的窗口信息的新值</param>  83     /// <returns></returns>  84     [DllImport("user32", EntryPoint = "SetWindowLong")]  85     private static extern uint SetWindowLong(IntPtr hwnd, int nIndex, uint dwNewLong);  86     #endregion  87   88     #region 从指定窗口的结构中取得信息  89     /// <summary>  90     /// 从指定窗口的结构中取得信息  91     /// </summary>  92     /// <param name="hwnd">欲为其获取信息的窗口的句柄</param>  93     /// <param name="nIndex">欲取回的信息</param>  94     /// <returns></returns>  95     [DllImport("user32", EntryPoint = "GetWindowLong")]  96     private static extern uint GetWindowLong(IntPtr hwnd, int nIndex);  97     #endregion  98   99     private const uint WS_EX_LAYERED = 0x80000; 100     private const int WS_EX_TRANSPARENT = 0x20; 101     private const int GWL_EXSTYLE = (-20); 102 }

1 public Form1() 2 { 3     InitializeComponent(); 4     new Watermark(this); 5 }