exrichtextbox.cs

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		/// <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 ...
		/// 
		/// {\rtf1\ansi\ansicpg1252\deff0\deflang1033{\fonttbl{[FONTS]}{\colortbl ;[COLORS]}}
		/// \viewkind4\uc1\pard\cf1\f0\fs20 [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 ...
		/// 
		/// \viewkind4\uc1\pard\cf1\f0\fs20 [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(@"\b");

			// 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("\n", @"\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(@"\b0");

			// 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 ...
		/// 
		/// {\pict\wmetafile8\picw[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(@"{\pict\wmetafile8");
			_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);