RichTextBoxEx

using System;
using System.Collections.Specialized;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;
using System.Windows.Forms;
namespace RichTextBoxEx.Controls
{
    #region Public Enums
    //可能的RTF颜色枚举
    public enum RtfColor
    {
        Black, Maroon, Green, Olive, Navy, Purple, Teal, Gray, Silver,
        Red, Lime, Yellow, Blue, Fuchsia, Aqua, White
    }
    #endregion
    /// <summary>
    /// This class adds the following functionality to RichTextBox:
    /// 
    /// 1. Allows plain text to be inserted or appended programmatically to RTF
    ///  content.
    /// 2. Allows the font, text color, and highlight color of plain text to be
    ///  specified when inserting or appending text as RTF.
    /// 3. Allows images to be inserted programmatically, or with interaction from
    ///  the user.
    /// </summary>
    /// <remarks>
    /// Many solutions to the problem of programmatically inserting images
    /// into a RichTextBox use the clipboard or hard code the RTF for
    /// the image in the program.  This class is an attempt to make the process of
    /// inserting images at runtime more flexible without the overhead of maintaining
    /// the clipboard or the use of huge, cumbersome strings.
    /// 
    /// RTF Specification v1.6 was used and is referred to many times in this document.
    /// http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnrtfspec/html/rtfspec.asp
    /// 
    /// For information about the RichEdit (Unmanaged RichTextBox) ...
    /// http://msdn.microsoft.com/library/default.asp?url=/library/en-us/shellcc/platform/commctls/richedit/richeditcontrols/aboutricheditcontrols.asp
    /// </remarks>
    public class ExRichTextBox : System.Windows.Forms.RichTextBox
    {
        #region My Enums
        // Specifies the flags/options for the unmanaged call to the GDI+ method
        // Metafile.EmfToWmfBits().
        private enum EmfToWmfBitsFlags
        {
            // Use the default conversion
            EmfToWmfBitsFlagsDefault = 0x00000000,
            // Embedded the source of the EMF metafiel within the resulting WMF
            // metafile
            EmfToWmfBitsFlagsEmbedEmf = 0x00000001,
            // Place a 22-byte header in the resulting WMF file.  The header is
            // required for the metafile to be considered placeable.
            EmfToWmfBitsFlagsIncludePlaceable = 0x00000002,
            // Don't simulate clipping by using the XOR operator.
            EmfToWmfBitsFlagsNoXORClip = 0x00000004
        };
        #endregion
        #region My Structs
        // Definitions for colors in an RTF document
        private struct RtfColorDef
        {
            public const string Black = @"
ed0green0lue0";
            public const string Maroon = @"
ed128green0lue0";
            public const string Green = @"
ed0green128lue0";
            public const string Olive = @"
ed128green128lue0";
            public const string Navy = @"
ed0green0lue128";
            public const string Purple = @"
ed128green0lue128";
            public const string Teal = @"
ed0green128lue128";
            public const string Gray = @"
ed128green128lue128";
            public const string Silver = @"
ed192green192lue192";
            public const string Red = @"
ed255green0lue0";
            public const string Lime = @"
ed0green255lue0";
            public const string Yellow = @"
ed255green255lue0";
            public const string Blue = @"
ed0green0lue255";
            public const string Fuchsia = @"
ed255green0lue255";
            public const string Aqua = @"
ed0green255lue255";
            public const string White = @"
ed255green255lue255";
        }
        // Control words for RTF font families
        private struct RtfFontFamilyDef
        {
            public const string Unknown = @"fnil";
            public const string Roman = @"froman";
            public const string Swiss = @"fswiss";
            public const string Modern = @"fmodern";
            public const string Script = @"fscript";
            public const string Decor = @"fdecor";
            public const string Technical = @"ftech";
            public const string BiDirect = @"fbidi";
        }
        #endregion
        #region My Constants
        // Not used in this application.  Descriptions can be found with documentation
        // of Windows GDI function SetMapMode
        private const int MM_TEXT = 1;
        private const int MM_LOMETRIC = 2;
        private const int MM_HIMETRIC = 3;
        private const int MM_LOENGLISH = 4;
        private const int MM_HIENGLISH = 5;
        private const int MM_TWIPS = 6;
        // Ensures that the metafile maintains a 1:1 aspect ratio
        private const int MM_ISOTROPIC = 7;
        // Allows the x-coordinates and y-coordinates of the metafile to be adjusted
        // independently
        private const int MM_ANISOTROPIC = 8;
        // Represents an unknown font family
        private const string FF_UNKNOWN = "UNKNOWN";
        // The number of hundredths of millimeters (0.01 mm) in an inch
        // For more information, see GetImagePrefix() method.
        private const int HMM_PER_INCH = 2540;
        // The number of twips in an inch
        // For more information, see GetImagePrefix() method.
        private const int TWIPS_PER_INCH = 1440;
        #endregion
        #region My Privates
        // The default text color
        private RtfColor textColor;
        // The default text background color
        private RtfColor highlightColor;
        // Dictionary that maps color enums to RTF color codes
        private HybridDictionary rtfColor;
        // Dictionary that mapas Framework font families to RTF font families
        private HybridDictionary rtfFontFamily;
        // The horizontal resolution at which the control is being displayed
        private float xDpi;
        // The vertical resolution at which the control is being displayed
        private float yDpi;
        #endregion
        #region Elements required to create an RTF document
        /* RTF HEADER
   * ----------
   * 
   * 
tf[N]  - For text to be considered to be RTF, it must be enclosed in this tag.
   *      rtf1 is used because the RichTextBox conforms to RTF Specification
   *      version 1.
   * ansi  - The character set.
   * ansicpg[N] - Specifies that unicode characters might be embedded. ansicpg1252
   *      is the default used by Windows.
   * deff[N]  - The default font. deff0 means the default font is the first font
   *      found.
   * deflang[N] - The default language. deflang1033 specifies US English.
   * */
        private const string RTF_HEADER = @"{
tf1ansiansicpg1252deff0deflang1033";
        /* RTF DOCUMENT AREA
         * -----------------
         * 
         * viewkind[N] - The type of view or zoom level.  viewkind4 specifies normal view.
         * uc[N]  - The number of bytes corresponding to a Unicode character.
         * pard  - Resets to default paragraph properties
         * cf[N]  - Foreground color.  cf1 refers to the color at index 1 in
         *      the color table
         * f[N]  - Font number. f0 refers to the font at index 0 in the font
         *      table.
         * fs[N]  - Font size in half-points.
         * */
        private const string RTF_DOCUMENT_PRE = @"viewkind4uc1pardcf1f0fs20";
        private const string RTF_DOCUMENT_POST = @"cf0fs17}";
        private string RTF_IMAGE_POST = @"}";
        #endregion
        #region Accessors
        // TODO: This can be ommitted along with RemoveBadCharacters
        // Overrides the default implementation of RTF.  This is done because the control
        // was originally developed to run in an instant messenger that uses the
        // Jabber XML-based protocol.  The framework would throw an exception when the
        // XML contained the null character, so I filtered out.
        public new string Rtf
        {
            get { return RemoveBadChars(base.Rtf); }
            set { base.Rtf = value; }
        }
        // The color of the text
        public RtfColor TextColor
        {
            get { return textColor; }
            set { textColor = value; }
        }
        // The color of the highlight
        public RtfColor HiglightColor
        {
            get { return highlightColor; }
            set { highlightColor = value; }
        }
        #endregion
        #region Constructors
        /// <summary>
        /// Initializes the text colors, creates dictionaries for RTF colors and
        /// font families, and stores the horizontal and vertical resolution of
        /// the RichTextBox's graphics context.
        /// </summary>
        public ExRichTextBox()
            : base()
        {
            // Initialize default text and background colors
            textColor = RtfColor.Black;
            highlightColor = RtfColor.White;
            // Initialize the dictionary mapping color codes to definitions
            rtfColor = new HybridDictionary();
            rtfColor.Add(RtfColor.Aqua, RtfColorDef.Aqua);
            rtfColor.Add(RtfColor.Black, RtfColorDef.Black);
            rtfColor.Add(RtfColor.Blue, RtfColorDef.Blue);
            rtfColor.Add(RtfColor.Fuchsia, RtfColorDef.Fuchsia);
            rtfColor.Add(RtfColor.Gray, RtfColorDef.Gray);
            rtfColor.Add(RtfColor.Green, RtfColorDef.Green);
            rtfColor.Add(RtfColor.Lime, RtfColorDef.Lime);
            rtfColor.Add(RtfColor.Maroon, RtfColorDef.Maroon);
            rtfColor.Add(RtfColor.Navy, RtfColorDef.Navy);
            rtfColor.Add(RtfColor.Olive, RtfColorDef.Olive);
            rtfColor.Add(RtfColor.Purple, RtfColorDef.Purple);
            rtfColor.Add(RtfColor.Red, RtfColorDef.Red);
            rtfColor.Add(RtfColor.Silver, RtfColorDef.Silver);
            rtfColor.Add(RtfColor.Teal, RtfColorDef.Teal);
            rtfColor.Add(RtfColor.White, RtfColorDef.White);
            rtfColor.Add(RtfColor.Yellow, RtfColorDef.Yellow);
            // Initialize the dictionary mapping default Framework font families to
            // RTF font families
            rtfFontFamily = new HybridDictionary();
            rtfFontFamily.Add(FontFamily.GenericMonospace.Name, RtfFontFamilyDef.Modern);
            rtfFontFamily.Add(FontFamily.GenericSansSerif, RtfFontFamilyDef.Swiss);
            rtfFontFamily.Add(FontFamily.GenericSerif, RtfFontFamilyDef.Roman);
            rtfFontFamily.Add(FF_UNKNOWN, RtfFontFamilyDef.Unknown);
            // Get the horizontal and vertical resolutions at which the object is
            // being displayed
            using (Graphics _graphics = this.CreateGraphics())
            {
                xDpi = _graphics.DpiX;
                yDpi = _graphics.DpiY;
            }
        }
        /// <summary>
        /// Calls the default constructor then sets the text color.
        /// </summary>
        /// <param name="_textColor"></param>
        public ExRichTextBox(RtfColor _textColor)
            : this()
        {
            textColor = _textColor;
        }
        /// <summary>
        /// Calls the default constructor then sets te text and highlight colors.
        /// </summary>
        /// <param name="_textColor"></param>
        /// <param name="_highlightColor"></param>
        public ExRichTextBox(RtfColor _textColor, RtfColor _highlightColor)
            : this()
        {
            textColor = _textColor;
            highlightColor = _highlightColor;
        }
        #endregion
        #region Append RTF or Text to RichTextBox Contents
        /// <summary>
        /// Assumes the string passed as a paramter is valid RTF text and attempts
        /// to append it as RTF to the content of the control.
        /// </summary>
        /// <param name="_rtf"></param>
        public void AppendRtf(string _rtf)
        {
            // Move caret to the end of the text
            this.Select(this.TextLength, 0);
            // Since SelectedRtf is null, this will append the string to the
            // end of the existing RTF
            this.SelectedRtf = _rtf;
        }
        /// <summary>
        /// Assumes that the string passed as a parameter is valid RTF text and
        /// attempts to insert it as RTF into the content of the control.
        /// </summary>
        /// <remarks>
        /// NOTE: The text is inserted wherever the caret is at the time of the call,
        /// and if any text is selected, that text is replaced.
        /// </remarks>
        /// <param name="_rtf"></param>
        public void InsertRtf(string _rtf)
        {
            this.SelectedRtf = _rtf;
        }
        /// <summary>
        /// Appends the text using the current font, text, and highlight colors.
        /// </summary>
        /// <param name="_text"></param>
        public void AppendTextAsRtf(string _text)
        {
            AppendTextAsRtf(_text, this.Font);
        }

        /// <summary>
        /// Appends the text using the given font, and current text and highlight
        /// colors.
        /// </summary>
        /// <param name="_text"></param>
        /// <param name="_font"></param>
        public void AppendTextAsRtf(string _text, Font _font)
        {
            AppendTextAsRtf(_text, _font, textColor);
        }
        /// <summary>
        /// Appends the text using the given font and text color, and the current
        /// highlight color.
        /// </summary>
        /// <param name="_text"></param>
        /// <param name="_font"></param>
        /// <param name="_color"></param>
        public void AppendTextAsRtf(string _text, Font _font, RtfColor _textColor)
        {
            AppendTextAsRtf(_text, _font, _textColor, highlightColor);
        }
        /// <summary>
        /// Appends the text using the given font, text, and highlight colors.  Simply
        /// moves the caret to the end of the RichTextBox's text and makes a call to
        /// insert.
        /// </summary>
        /// <param name="_text"></param>
        /// <param name="_font"></param>
        /// <param name="_textColor"></param>
        /// <param name="_backColor"></param>
        public void AppendTextAsRtf(string _text, Font _font, RtfColor _textColor, RtfColor _backColor)
        {
            // Move carret to the end of the text
            this.Select(this.TextLength, 0);
            InsertTextAsRtf(_text, _font, _textColor, _backColor);
        }
        #endregion
        #region Insert Plain Text
        /// <summary>
        /// Inserts the text using the current font, text, and highlight colors.
        /// </summary>
        /// <param name="_text"></param>
        public void InsertTextAsRtf(string _text)
        {
            InsertTextAsRtf(_text, this.Font);
        }

        /// <summary>
        /// Inserts the text using the given font, and current text and highlight
        /// colors.
        /// </summary>
        /// <param name="_text"></param>
        /// <param name="_font"></param>
        public void InsertTextAsRtf(string _text, Font _font)
        {
            InsertTextAsRtf(_text, _font, textColor);
        }
        /// <summary>
        /// Inserts the text using the given font and text color, and the current
        /// highlight color.
        /// </summary>
        /// <param name="_text"></param>
        /// <param name="_font"></param>
        /// <param name="_color"></param>
        public void InsertTextAsRtf(string _text, Font _font, RtfColor _textColor)
        {
            InsertTextAsRtf(_text, _font, _textColor, highlightColor);
        }
        /// <summary>
        /// Inserts the text using the given font, text, and highlight colors.  The
        /// text is wrapped in RTF codes so that the specified formatting is kept.
        /// You can only assign valid RTF to the RichTextBox.Rtf property, else
        /// an exception is thrown.  The RTF string should follow this format ...
        /// 
        /// {
tf1ansiansicpg1252deff0deflang1033{fonttbl{[FONTS]}{colortbl ;[COLORS]}}
        /// viewkind4uc1pardcf1f0fs20 [DOCUMENT AREA] }
        /// 
        /// </summary>
        /// <remarks>
        /// NOTE: The text is inserted wherever the caret is at the time of the call,
        /// and if any text is selected, that text is replaced.
        /// </remarks>
        /// <param name="_text"></param>
        /// <param name="_font"></param>
        /// <param name="_color"></param>
        /// <param name="_color"></param>
        public void InsertTextAsRtf(string _text, Font _font, RtfColor _textColor, RtfColor _backColor)
        {
            StringBuilder _rtf = new StringBuilder();
            // Append the RTF header
            _rtf.Append(RTF_HEADER);
            // Create the font table from the font passed in and append it to the
            // RTF string
            _rtf.Append(GetFontTable(_font));
            // Create the color table from the colors passed in and append it to the
            // RTF string
            _rtf.Append(GetColorTable(_textColor, _backColor));
            // Create the document area from the text to be added as RTF and append
            // it to the RTF string.
            _rtf.Append(GetDocumentArea(_text, _font));
            this.SelectedRtf = _rtf.ToString();
        }
        /// <summary>
        /// Creates the Document Area of the RTF being inserted. The document area
        /// (in this case) consists of the text being added as RTF and all the
        /// formatting specified in the Font object passed in. This should have the
        /// form ...
        /// 
        /// viewkind4uc1pardcf1f0fs20 [DOCUMENT AREA] }
        ///
        /// </summary>
        /// <param name="_text"></param>
        /// <param name="_font"></param>
        /// <returns>
        /// The document area as a string.
        /// </returns>
        private string GetDocumentArea(string _text, Font _font)
        {
            StringBuilder _doc = new StringBuilder();
            // Append the standard RTF document area control string
            _doc.Append(RTF_DOCUMENT_PRE);
            // Set the highlight color (the color behind the text) to the
            // third color in the color table.  See GetColorTable for more details.
            _doc.Append(@"highlight2");
            // If the font is bold, attach corresponding tag
            if (_font.Bold)
                _doc.Append(@"");
            // If the font is italic, attach corresponding tag
            if (_font.Italic)
                _doc.Append(@"i");
            // If the font is strikeout, attach corresponding tag
            if (_font.Strikeout)
                _doc.Append(@"strike");
            // If the font is underlined, attach corresponding tag
            if (_font.Underline)
                _doc.Append(@"ul");
            // Set the font to the first font in the font table.
            // See GetFontTable for more details.
            _doc.Append(@"f0");
            // Set the size of the font.  In RTF, font size is measured in
            // half-points, so the font size is twice the value obtained from
            // Font.SizeInPoints
            _doc.Append(@"fs");
            _doc.Append((int)Math.Round((2 * _font.SizeInPoints)));
            // Apppend a space before starting actual text (for clarity)
            _doc.Append(@" ");
            // Append actual text, however, replace newlines with RTF par.
            // Any other special text should be handled here (e.g.) tabs, etc.
            _doc.Append(_text.Replace("
", @"par "));
            // RTF isn't strict when it comes to closing control words, but what the
            // heck ...
            // Remove the highlight
            _doc.Append(@"highlight0");
            // If font is bold, close tag
            if (_font.Bold)
                _doc.Append(@"0");
            // If font is italic, close tag
            if (_font.Italic)
                _doc.Append(@"i0");
            // If font is strikeout, close tag
            if (_font.Strikeout)
                _doc.Append(@"strike0");
            // If font is underlined, cloes tag
            if (_font.Underline)
                _doc.Append(@"ulnone");
            // Revert back to default font and size
            _doc.Append(@"f0");
            _doc.Append(@"fs20");
            // Close the document area control string
            _doc.Append(RTF_DOCUMENT_POST);
            return _doc.ToString();
        }
        #endregion
        #region Insert Image
        /// <summary>
        /// Inserts an image into the RichTextBox.  The image is wrapped in a Windows
        /// Format Metafile, because although Microsoft discourages the use of a WMF,
        /// the RichTextBox (and even MS Word), wraps an image in a WMF before inserting
        /// the image into a document.  The WMF is attached in HEX format (a string of
        /// HEX numbers).
        /// 
        /// The RTF Specification v1.6 says that you should be able to insert bitmaps,
        /// .jpegs, .gifs, .pngs, and Enhanced Metafiles (.emf) directly into an RTF
        /// document without the WMF wrapper. This works fine with MS Word,
        /// however, when you don't wrap images in a WMF, WordPad and
        /// RichTextBoxes simply ignore them.  Both use the riched20.dll or msfted.dll.
        /// </summary>
        /// <remarks>
        /// NOTE: The image is inserted wherever the caret is at the time of the call,
        /// and if any text is selected, that text is replaced.
        /// </remarks>
        /// <param name="_image"></param>
        public void InsertImage(Image _image)
        {
            StringBuilder _rtf = new StringBuilder();
            // Append the RTF header
            _rtf.Append(RTF_HEADER);
            // Create the font table using the RichTextBox's current font and append
            // it to the RTF string
            _rtf.Append(GetFontTable(this.Font));
            // Create the image control string and append it to the RTF string
            _rtf.Append(GetImagePrefix(_image));
            // Create the Windows Metafile and append its bytes in HEX format
            _rtf.Append(GetRtfImage(_image));
            // Close the RTF image control string
            _rtf.Append(RTF_IMAGE_POST);
            this.SelectedRtf = _rtf.ToString();
        }
        /// <summary>
        /// Creates the RTF control string that describes the image being inserted.
        /// This description (in this case) specifies that the image is an
        /// MM_ANISOTROPIC metafile, meaning that both X and Y axes can be scaled
        /// independently.  The control string also gives the images current dimensions,
        /// and its target dimensions, so if you want to control the size of the
        /// image being inserted, this would be the place to do it. The prefix should
        /// have the form ...
        /// 
        /// {pictwmetafile8picw[A]pich[B]picwgoal[C]pichgoal[D]
        /// 
        /// where ...
        /// 
        /// A = current width of the metafile in hundredths of millimeters (0.01mm)
        ///  = Image Width in Inches * Number of (0.01mm) per inch
        ///  = (Image Width in Pixels / Graphics Context's Horizontal Resolution) * 2540
        ///  = (Image Width in Pixels / Graphics.DpiX) * 2540
        /// 
        /// B = current height of the metafile in hundredths of millimeters (0.01mm)
        ///  = Image Height in Inches * Number of (0.01mm) per inch
        ///  = (Image Height in Pixels / Graphics Context's Vertical Resolution) * 2540
        ///  = (Image Height in Pixels / Graphics.DpiX) * 2540
        /// 
        /// C = target width of the metafile in twips
        ///  = Image Width in Inches * Number of twips per inch
        ///  = (Image Width in Pixels / Graphics Context's Horizontal Resolution) * 1440
        ///  = (Image Width in Pixels / Graphics.DpiX) * 1440
        /// 
        /// D = target height of the metafile in twips
        ///  = Image Height in Inches * Number of twips per inch
        ///  = (Image Height in Pixels / Graphics Context's Horizontal Resolution) * 1440
        ///  = (Image Height in Pixels / Graphics.DpiX) * 1440
        /// 
        /// </summary>
        /// <remarks>
        /// The Graphics Context's resolution is simply the current resolution at which
        /// windows is being displayed.  Normally it's 96 dpi, but instead of assuming
        /// I just added the code.
        /// 
        /// According to Ken Howe at pbdr.com, "Twips are screen-independent units
        /// used to ensure that the placement and proportion of screen elements in
        /// your screen application are the same on all display systems."
        /// 
        /// Units Used
        /// ----------
        /// 1 Twip = 1/20 Point
        /// 1 Point = 1/72 Inch
        /// 1 Twip = 1/1440 Inch
        /// 
        /// 1 Inch = 2.54 cm
        /// 1 Inch = 25.4 mm
        /// 1 Inch = 2540 (0.01)mm
        /// </remarks>
        /// <param name="_image"></param>
        /// <returns></returns>
        private string GetImagePrefix(Image _image)
        {
            StringBuilder _rtf = new StringBuilder();
            // Calculate the current width of the image in (0.01)mm
            int picw = (int)Math.Round((_image.Width / xDpi) * HMM_PER_INCH);
            // Calculate the current height of the image in (0.01)mm
            int pich = (int)Math.Round((_image.Height / yDpi) * HMM_PER_INCH);
            // Calculate the target width of the image in twips
            int picwgoal = (int)Math.Round((_image.Width / xDpi) * TWIPS_PER_INCH);
            // Calculate the target height of the image in twips
            int pichgoal = (int)Math.Round((_image.Height / yDpi) * TWIPS_PER_INCH);
            // Append values to RTF string
            _rtf.Append(@"{pictwmetafile8");
            _rtf.Append(@"picw");
            _rtf.Append(picw);
            _rtf.Append(@"pich");
            _rtf.Append(pich);
            _rtf.Append(@"picwgoal");
            _rtf.Append(picwgoal);
            _rtf.Append(@"pichgoal");
            _rtf.Append(pichgoal);
            _rtf.Append(" ");
            return _rtf.ToString();
        }
        /// <summary>
        /// Use the EmfToWmfBits function in the GDI+ specification to convert a 
        /// Enhanced Metafile to a Windows Metafile
        /// </summary>
        /// <param name="_hEmf">
        /// A handle to the Enhanced Metafile to be converted
        /// </param>
        /// <param name="_bufferSize">
        /// The size of the buffer used to store the Windows Metafile bits returned
        /// </param>
        /// <param name="_buffer">
        /// An array of bytes used to hold the Windows Metafile bits returned
        /// </param>
        /// <param name="_mappingMode">
        /// The mapping mode of the image.  This control uses MM_ANISOTROPIC.
        /// </param>
        /// <param name="_flags">
        /// Flags used to specify the format of the Windows Metafile returned
        /// </param>
        [DllImportAttribute("gdiplus.dll")]
        private static extern uint GdipEmfToWmfBits(IntPtr _hEmf, uint _bufferSize,
            byte[] _buffer, int _mappingMode, EmfToWmfBitsFlags _flags);

        /// <summary>
        /// Wraps the image in an Enhanced Metafile by drawing the image onto the
        /// graphics context, then converts the Enhanced Metafile to a Windows
        /// Metafile, and finally appends the bits of the Windows Metafile in HEX
        /// to a string and returns the string.
        /// </summary>
        /// <param name="_image"></param>
        /// <returns>
        /// A string containing the bits of a Windows Metafile in HEX
        /// </returns>
        private string GetRtfImage(Image _image)
        {
            StringBuilder _rtf = null;
            // Used to store the enhanced metafile
            MemoryStream _stream = null;
            // Used to create the metafile and draw the image
            Graphics _graphics = null;
            // The enhanced metafile
            Metafile _metaFile = null;
            // Handle to the device context used to create the metafile
            IntPtr _hdc;
            try
            {
                _rtf = new StringBuilder();
                _stream = new MemoryStream();
                // Get a graphics context from the RichTextBox
                using (_graphics = this.CreateGraphics())
                {
                    // Get the device context from the graphics context
                    _hdc = _graphics.GetHdc();
                    // Create a new Enhanced Metafile from the device context
                    _metaFile = new Metafile(_stream, _hdc);
                    // Release the device context
                    _graphics.ReleaseHdc(_hdc);
                }
                // Get a graphics context from the Enhanced Metafile
                using (_graphics = Graphics.FromImage(_metaFile))
                {
                    // Draw the image on the Enhanced Metafile
                    _graphics.DrawImage(_image, new Rectangle(0, 0, _image.Width, _image.Height));
                }
                // Get the handle of the Enhanced Metafile
                IntPtr _hEmf = _metaFile.GetHenhmetafile();
                // A call to EmfToWmfBits with a null buffer return the size of the
                // buffer need to store the WMF bits.  Use this to get the buffer
                // size.
                uint _bufferSize = GdipEmfToWmfBits(_hEmf, 0, null, MM_ANISOTROPIC,
                    EmfToWmfBitsFlags.EmfToWmfBitsFlagsDefault);
                // Create an array to hold the bits
                byte[] _buffer = new byte[_bufferSize];
                // A call to EmfToWmfBits with a valid buffer copies the bits into the
                // buffer an returns the number of bits in the WMF.  
                uint _convertedSize = GdipEmfToWmfBits(_hEmf, _bufferSize, _buffer, MM_ANISOTROPIC,
                    EmfToWmfBitsFlags.EmfToWmfBitsFlagsDefault);
                // Append the bits to the RTF string
                for (int i = 0; i < _buffer.Length; ++i)
                {
                    _rtf.Append(String.Format("{0:X2}", _buffer[i]));
                }
                return _rtf.ToString();
            }
            finally
            {
                if (_graphics != null)
                    _graphics.Dispose();
                if (_metaFile != null)
                    _metaFile.Dispose();
                if (_stream != null)
                    _stream.Close();
            }
        }
        #endregion
        #region RTF Helpers
        /// <summary>
        /// Creates a font table from a font object.  When an Insert or Append 
        /// operation is performed a font is either specified or the default font
        /// is used.  In any case, on any Insert or Append, only one font is used,
        /// thus the font table will always contain a single font.  The font table
        /// should have the form ...
        /// 
        /// {fonttbl{f0[FAMILY]fcharset0 [FONT_NAME];}
        /// </summary>
        /// <param name="_font"></param>
        /// <returns></returns>
        private string GetFontTable(Font _font)
        {
            StringBuilder _fontTable = new StringBuilder();
            // Append table control string
            _fontTable.Append(@"{fonttbl{f0");
            _fontTable.Append(@"");
            // If the font's family corresponds to an RTF family, append the
            // RTF family name, else, append the RTF for unknown font family.
            if (rtfFontFamily.Contains(_font.FontFamily.Name))
                _fontTable.Append(rtfFontFamily[_font.FontFamily.Name]);
            else
                _fontTable.Append(rtfFontFamily[FF_UNKNOWN]);
            // fcharset specifies the character set of a font in the font table.
            // 0 is for ANSI.
            _fontTable.Append(@"fcharset0 ");
            // Append the name of the font
            _fontTable.Append(_font.Name);
            // Close control string
            _fontTable.Append(@";}}");
            return _fontTable.ToString();
        }
        /// <summary>
        /// Creates a font table from the RtfColor structure.  When an Insert or Append
        /// operation is performed, _textColor and _backColor are either specified
        /// or the default is used.  In any case, on any Insert or Append, only three
        /// colors are used.  The default color of the RichTextBox (signified by a
        /// semicolon (;) without a definition), is always the first color (index 0) in
        /// the color table.  The second color is always the text color, and the third
        /// is always the highlight color (color behind the text).  The color table
        /// should have the form ...
        /// 
        /// {colortbl ;[TEXT_COLOR];[HIGHLIGHT_COLOR];}
        /// 
        /// </summary>
        /// <param name="_textColor"></param>
        /// <param name="_backColor"></param>
        /// <returns></returns>
        private string GetColorTable(RtfColor _textColor, RtfColor _backColor)
        {
            StringBuilder _colorTable = new StringBuilder();
            // Append color table control string and default font (;)
            _colorTable.Append(@"{colortbl ;");
            // Append the text color
            _colorTable.Append(rtfColor[_textColor]);
            _colorTable.Append(@";");
            // Append the highlight color
            _colorTable.Append(rtfColor[_backColor]);
            _colorTable.Append(@";}
");
            return _colorTable.ToString();
        }
        /// <summary>
        /// Called by overrided RichTextBox.Rtf accessor.
        /// Removes the null character from the RTF.  This is residue from developing
        /// the control for a specific instant messaging protocol and can be ommitted.
        /// </summary>
        /// <param name="_originalRtf"></param>
        /// <returns>RTF without null character</returns>
        private string RemoveBadChars(string _originalRtf)
        {
            return _originalRtf.Replace("", "");
        }
        #endregion
    }
}