Insert Image at Cursor Position in Rich Text box

c#, image, richtextbox, winforms

Solution

I've prepared a fully functional example for you using the solution posted here exploiting the RTF power.

As Hans Passant wrote: the solution is quite tricky and there are some valid alternatives to achieve it.

BTW, this is your code (rewrited):

private bool CheckIfImage(string filename)
{
        var valids = new[] {".jpeg", ".jpg", ".png", ".ico", ".gif", ".bmp", ".emp", ".wmf", ".tiff"};
        return valids.Contains(System.IO.Path.GetExtension(filename));
}

private void openFileDialog2_FileOk(object sender, CancelEventArgs e)
{
    if (CheckIfImage(openFileDialog2.FileName.ToLower()) == true)
        embedImage(Image.FromFile(openFileDialog2.FileName));
    else
        MessageBox.Show("Invalid Image File Selected");
}

This is the `embedImage` method:

    private void embedImage(Image img)
    {
        var rtf = new StringBuilder();

        // Append the RTF header
        rtf.Append(@"{\rtf1\ansi\ansicpg1252\deff0\deflang1033");
        // 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(img));
        // Create the Windows Metafile and append its bytes in HEX format
        rtf.Append(getRtfImage(img));
        // Close the RTF image control string
        rtf.Append(@"}");
        richTextBox1.SelectedRtf = rtf.ToString();
    }

Here there are all the necessary methods:

    private enum EmfToWmfBitsFlags
    {
        EmfToWmfBitsFlagsDefault = 0x00000000,
        EmfToWmfBitsFlagsEmbedEmf = 0x00000001,
        EmfToWmfBitsFlagsIncludePlaceable = 0x00000002,
        EmfToWmfBitsFlagsNoXORClip = 0x00000004
    };

    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";
    }

    [DllImport("gdiplus.dll")]
    private static extern uint GdipEmfToWmfBits(IntPtr _hEmf,
      uint _bufferSize, byte[] _buffer,
      int _mappingMode, EmfToWmfBitsFlags _flags);


    private string GetFontTable(Font font)
    {
        var fontTable = new StringBuilder();
        // Append table control string
        fontTable.Append(@"{\fonttbl{\f0");
        fontTable.Append(@"\");
        var rtfFontFamily = new HybridDictionary();
        rtfFontFamily.Add(FontFamily.GenericMonospace.Name, RtfFontFamilyDef.Modern);
        rtfFontFamily.Add(FontFamily.GenericSansSerif, RtfFontFamilyDef.Swiss);
        rtfFontFamily.Add(FontFamily.GenericSerif, RtfFontFamilyDef.Roman);
        rtfFontFamily.Add("UNKNOWN", RtfFontFamilyDef.Unknown);

        // If the font's family corresponds to an RTF family, append the
        // RTF family name, else, append the RTF for unknown font family.
        fontTable.Append(rtfFontFamily.Contains(font.FontFamily.Name) ? rtfFontFamily[font.FontFamily.Name] : rtfFontFamily["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();
    }

    private string GetImagePrefix(Image _image)
    {
        float xDpi, yDpi;
        var rtf = new StringBuilder();
        using (Graphics graphics = CreateGraphics())
        {
            xDpi = graphics.DpiX;
            yDpi = graphics.DpiY;
        }
        // Calculate the current width of the image in (0.01)mm
        var picw = (int)Math.Round((_image.Width / xDpi) * 2540);
        // Calculate the current height of the image in (0.01)mm
        var pich = (int)Math.Round((_image.Height / yDpi) * 2540);
        // Calculate the target width of the image in twips
        var picwgoal = (int)Math.Round((_image.Width / xDpi) * 1440);
        // Calculate the target height of the image in twips
        var pichgoal = (int)Math.Round((_image.Height / yDpi) * 1440);
        // 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();
    }

    private string getRtfImage(Image image)
    {
        // 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;
        try
        {
            var rtf = new StringBuilder();
            stream = new MemoryStream();
            // Get a graphics context from the RichTextBox
            using (graphics = CreateGraphics())
            {
                // Get the device context from the graphics context
                IntPtr 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, 8, EmfToWmfBitsFlags.EmfToWmfBitsFlagsDefault);
            // Create an array to hold the bits
            var 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, 8, EmfToWmfBitsFlags.EmfToWmfBitsFlagsDefault);
            // Append the bits to the RTF string
            foreach (byte t in buffer)
            {
                rtf.Append(String.Format("{0:X2}", t));
            }
            return rtf.ToString();
        }
        finally
        {
            if (graphics != null)
                graphics.Dispose();
            if (metaFile != null)
                metaFile.Dispose();
            if (stream != null)
                stream.Close();
        }
    }

I suggest you to wrap this into your own `UserControl`.

Problem

Original source

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