c#控件RichTextBox扩展之插入图片

以下是关于扩展插入图片的代码：由于其他功能和本身提供的一样故在这里就不再贴代码了，只是把其中的关于插入图片的封装贴出来。

#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 des cription (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);

                    // 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