如何打印 RichTextBox

// 与 Win32接口通信 [DllImport("USER32.dll")]private static extern Int32 SendMessage(IntPtr hWnd, int msg, int wParam, IntPtr lParam);private const int WM_USER = 0x400;private const int EM_FORMATRANGE = WM_USER + 57;private const double inch = 14.4; // 与象素的换算。 // 再是所需要的结构体的定义： [StructLayout(LayoutKind.Sequential)]private struct RECT{    public int Left;    public int Top;    public int Right;    public int Bottom;}// 望文生义吧 [StructLayout(LayoutKind.Sequential)]private struct CHARRANGE{    public int cpMin;    public int cpMax;}[StructLayout(LayoutKind.Sequential)]private struct FORMATRANGE{    public IntPtr hdc;    public IntPtr hdcTarget;    public RECT rc;    public RECT rcPage;    public CHARRANGE chrg;}// 将RTB上的内容格式化后画出来 public static Bitmap RtbToBitmap(RichTextBox rtb){    // 这个地方是可打印的大小    return RtbToBitmap(rtb, rtb.Bounds.Width, rtb.Bounds.Height * 2);}public static Bitmap RtbToBitmap(RichTextBox rtb, int width, int height){    Bitmap bmp = new Bitmap(width, height);    for (int i = 0; i < width; i++)    {        for (int j = 0; j < height; j++)        {            bmp.SetPixel(i, j, Color.White);        }    }    using (Graphics gr = Graphics.FromImage(bmp))    {        System.IntPtr hDC = gr.GetHdc(); // 屏幕做为画源         FORMATRANGE fmtRange;        RECT rect;        int fromAPI;        rect.Top = 0; rect.Left = 0;        rect.Bottom = (int)(bmp.Height + (bmp.Height * (bmp.HorizontalResolution / 100)) * inch);        rect.Right = (int)(bmp.Width + (bmp.Width * (bmp.VerticalResolution / 100)) * inch);        fmtRange.chrg.cpMin = 0;        fmtRange.chrg.cpMax = -1;        fmtRange.hdc = hDC;        fmtRange.hdcTarget = hDC;        fmtRange.rc = rect;        fmtRange.rcPage = rect;        int wParam = 1;        System.IntPtr lParam = System.Runtime.InteropServices.Marshal.AllocCoTaskMem(Marshal.SizeOf(fmtRange));        System.Runtime.InteropServices.Marshal.StructureToPtr(fmtRange, lParam, false);        fromAPI = SendMessage(rtb.Handle, EM_FORMATRANGE, wParam, lParam);        System.Runtime.InteropServices.Marshal.FreeCoTaskMem(lParam);        fromAPI = SendMessage(rtb.Handle, EM_FORMATRANGE, wParam, new IntPtr(0));        gr.ReleaseHdc(hDC);    }    return bmp;}