System.Drawing.Drawing2D.GraphicsPath shape = new System.Drawing.Drawing2D.GraphicsPath(); shape.AddEllipse(0,0,this.Height, this.Width); this.Region = new Region(shape); 

class BitmapRegion {   public BitmapRegion()   { }     /// <summary>    /// Create and apply the region on the supplied control   /// 創建支持位圖區域的控件（目前有button和form）   /// </summary>    /// <param name="control">The Control object to apply the region to控件</param>    /// <param name="bitmap">The Bitmap object to create the region from位圖</param>    public static void CreateControlRegion(Control control, Bitmap bitmap)   {     // Return if control and bitmap are null     //判斷是否存在控件和位圖     if (control == null || bitmap == null)       return;      // Set our control''s size to be the same as the bitmap     //設置控件大小為位圖大小     control.Width = bitmap.Width;     control.Height = bitmap.Height;     // Check if we are dealing with Form here      //當控件是form時     if (control is System.Windows.Forms.Form)     {       // Cast to a Form object       //強制轉換為FORM       Form form = (Form)control;       // Set our form''s size to be a little larger that the bitmap just        // in case the form''s border style is not set to none in the first place        //當FORM的邊界FormBorderStyle不為NONE時，應將FORM的大小設置成比位圖大小稍大一點       form.Width = control.Width;       form.Height = control.Height;       // No border        //沒有邊界       form.FormBorderStyle = FormBorderStyle.None;       // Set bitmap as the background image        //將位圖設置成窗體背景圖片       form.BackgroundImage = bitmap;       // Calculate the graphics path based on the bitmap supplied        //計算位圖中不透明部分的邊界       GraphicsPath graphicsPath = CalculateControlGraphicsPath(bitmap);       // Apply new region        //應用新的區域       form.Region = new Region(graphicsPath);     }     // Check if we are dealing with Button here      //當控件是button時     else if (control is System.Windows.Forms.Button)     {       // Cast to a button object        //強制轉換為 button       Button button = (Button)control;       // Do not show button text        //不顯示button text       button.Text = "";        // Change cursor to hand when over button        //改變 cursor的style       button.Cursor = Cursors.Hand;       // Set background image of button        //設置button的背景圖片       button.BackgroundImage = bitmap;        // Calculate the graphics path based on the bitmap supplied        //計算位圖中不透明部分的邊界       GraphicsPath graphicsPath = CalculateControlGraphicsPath(bitmap);       // Apply new region        //應用新的區域       button.Region = new Region(graphicsPath);     }   }   /// <summary>    /// Calculate the graphics path that representing the figure in the bitmap    /// excluding the transparent color which is the top left pixel.    /// //計算位圖中不透明部分的邊界   /// </summary>  /// <param name="bitmap">The Bitmap object to calculate our graphics path from</param>    /// <returns>Calculated graphics path</returns>    private static GraphicsPath CalculateControlGraphicsPath(Bitmap bitmap)   {     // Create GraphicsPath for our bitmap calculation      //創建 GraphicsPath     GraphicsPath graphicsPath = new GraphicsPath();     // Use the top left pixel as our transparent color      //使用左上角的一點的顏色作為我們透明色     Color colorTransparent = bitmap.GetPixel(0, 0);     // This is to store the column value where an opaque pixel is first found.    // This value will determine where we start scanning for trailing opaque pixels.     //第一個找到點的X     int colOpaquePixel = 0;     // Go through all rows (Y axis)      // 偏歷所有行（Y方向）     for (int row = 0; row < bitmap.Height; row++)     {       // Reset value        //重設       colOpaquePixel = 0;       // Go through all columns (X axis)        //偏歷所有列（X方向）       for (int col = 0; col < bitmap.Width; col++)       {     // If this is an opaque pixel, mark it and search for anymore trailing behind          //如果是不需要透明處理的點則標記，然后繼續偏歷         if (bitmap.GetPixel(col, row) != colorTransparent)         {           // Opaque pixel found, mark current position           //記錄當前           colOpaquePixel = col;        // Create another variable to set the current pixel position            //建立新變量來記錄當前點           int colNext = col;         // Starting from current found opaque pixel, search for anymore opaque pixels        // trailing behind, until a transparent  pixel is found or minimum width is reached            ///從找到的不透明點開始，繼續尋找不透明點,一直到找到或則達到圖片寬度          for (colNext = colOpaquePixel; colNext < bitmap.Width; colNext++)             if (bitmap.GetPixel(colNext, row) == colorTransparent)               break;       // Form a rectangle for line of opaque  pixels found and add it to our graphics path            //將不透明點加到graphics path       graphicsPath.AddRectangle(new Rectangle(colOpaquePixel, row, colNext - colOpaquePixel, 1));           // No need to scan the line of opaque pixels just found            col = colNext;         }       }     }     // Return calculated graphics path      return graphicsPath;   } } 

public Form3()     {       InitializeComponent();       //創建不規則窗體       POINTAPI[] poin;       poin = new POINTAPI[5];       poin[0].x = 90;       poin[0].y = 90;       poin[1].x = this.Width;       poin[1].y = 0;       poin[2].x = Width;       poin[2].y = this.Height / 2;       poin[3].x = Width / 2;       poin[3].y = Height / 2;       poin[4].x = 0;       poin[4].y = Width;       Boolean flag = true;       IntPtr hRgn = CreatePolygonRgn(ref poin[0], 8, 1);       SetWindowRgn(this.Handle, hRgn, ref flag);       this.BackColor = Color.BurlyWood;     }     [StructLayout(LayoutKind.Sequential)]     private struct POINTAPI     {       internal int x;       internal int y;     }     [DllImport("gdi32.dll")]  private static extern IntPtr CreatePolygonRgn(ref POINTAPI lpPoint,int nCount,int nPolyFillMode);     [DllImport("user32.dll")]  private static extern IntPtr SetWindowRgn(IntPtr hWnd,IntPtr hRgn, ref Boolean bRedraw);     //設置窗體顯示狀態     [DllImport("user32.dll")] private static extern int SetWindowPos(IntPtr hwnd,int hWndInsertAfter,int x,int y,int cx,int cy,int wFlags);     private void Start_Btn_Click(object sender, EventArgs e)     {//始終顯示在前面       SetWindowPos(this.Handle, -1, 0, 0, 0, 0, 1);     }     private void button1_Click(object sender, EventArgs e)     {       //最小化始終顯示在前面       SetWindowPos(this.Handle, -1, 0, 0, 0, 0, 0);     }