c# - Printing content of RichTextBox to image in WYSIWYG mode

[Vincent]

Dear all,

I have implemented a class to export the content of RichTextBox to
image in WYSISYG mode so that line breaks on the screen are the same as
exported.
C# Code:
[ StructLayout( LayoutKind.Sequential )]
public struct STRUCT_RECT
{
public Int32 left;
public Int32 top;
public Int32 right;
public Int32 bottom;
}

[ StructLayout( LayoutKind.Sequential )]
public struct STRUCT_CHARRANGE
{
public Int32 cpMin;
public Int32 cpMax;
}

[ StructLayout( LayoutKind.Sequential )]
public struct STRUCT_FORMATRANGE
{
public IntPtr hdc;
public IntPtr hdcTarget;
public STRUCT_RECT rc;
public STRUCT_RECT rcPage;
public STRUCT_CHARRANGE chrg;
}
/// <summary>
/// Summary description for RtfToPicture2.
/// </summary>
public class RtfToPicture2
{
public RtfToPicture2()
{
//
// TODO: Add constructor logic here
//
}

[DllImport("user32.dll")]
private static extern Int32 SendMessage(IntPtr hWnd, Int32 msg, Int32
wParam, IntPtr lParam);

private const Int32 WM_USER = 0x400;
private const Int32 EM_FORMATRANGE = WM_USER+57;


private int m_nFirstCharOnPage;

// C#
/// <summary>
/// Calculate or render the contents of our RichTextBox for printing
/// </summary>
/// <param name="measureOnly">If true, only the calculation is
performed,
/// otherwise the text is rendered as well</param>
/// <param name="e">The PrintPageEventArgs object from the
/// PrintPage event</param>
/// <param name="charFrom">Index of first character to be
printed</param>
/// <param name="charTo">Index of last character to be
printed</param>
/// <returns>(Index of last character that fitted on the
/// page) + 1</returns>
//public int FormatRange(bool measureOnly, PrintPageEventArgs e, int
charFrom, int charTo)
public int FormatRange(bool measureOnly, ref RichTextBox RTB,
PictureBox pb, int charFrom, int charTo)
{
// Specify which characters to print
STRUCT_CHARRANGE cr;
cr.cpMin = charFrom;
cr.cpMax = charTo;

// Specify the area inside page margins
STRUCT_RECT rc;
rc.top = HundredthInchToTwips(0);
rc.bottom = HundredthInchToTwips(pb.Height);
rc.left = HundredthInchToTwips(0);
rc.right = HundredthInchToTwips(pb.Width);

// Specify the page area
STRUCT_RECT rcPage;
rcPage.top = HundredthInchToTwips(0);
rcPage.bottom = HundredthInchToTwips(pb.Height);
rcPage.left = HundredthInchToTwips(0);
rcPage.right = HundredthInchToTwips(pb.Width);

// Get device context of output device
Graphics g = pb.CreateGraphics();
IntPtr hdc = g.GetHdc();

// Fill in the FORMATRANGE struct
STRUCT_FORMATRANGE fr;
fr.chrg = cr;
fr.hdc = hdc;
fr.hdcTarget = hdc;
fr.rc = rc;
fr.rcPage = rcPage;

// Non-Zero wParam means render, Zero means measure
Int32 wParam = (measureOnly ? 0 : 1);

// Allocate memory for the FORMATRANGE struct and
// copy the contents of our struct to this memory
IntPtr lParam = Marshal.AllocCoTaskMem( Marshal.SizeOf( fr ) );
Marshal.StructureToPtr(fr, lParam, false);

// Send the actual Win32 message
int res = SendMessage(RTB.Handle, EM_FORMATRANGE, wParam, lParam);

// Free allocated memory
Marshal.FreeCoTaskMem(lParam);

// and release the device context
g.ReleaseHdc(hdc);

g.Dispose();

return res;
}

public int FormatRange(bool measureOnly, ref RichTextBox RTB, ref
Bitmap b, int charFrom, int charTo)
{
// Specify which characters to print
STRUCT_CHARRANGE cr;
cr.cpMin = charFrom;
cr.cpMax = charTo;

// Specify the area inside page margins
STRUCT_RECT rc;
rc.top = HundredthInchToTwips(0);
rc.bottom = HundredthInchToTwips(b.Height);
rc.left = HundredthInchToTwips(0);
rc.right = HundredthInchToTwips(b.Width);

// Specify the page area
STRUCT_RECT rcPage;
rcPage.top = HundredthInchToTwips(0);
rcPage.bottom = HundredthInchToTwips(b.Height);
rcPage.left = HundredthInchToTwips(0);
rcPage.right = HundredthInchToTwips(b.Width);

// Get device context of output device
Graphics g = Graphics.FromImage(b);
IntPtr hdc = g.GetHdc();

// Fill in the FORMATRANGE struct
STRUCT_FORMATRANGE fr;
fr.chrg = cr;
fr.hdc = hdc;
fr.hdcTarget = hdc;
fr.rc = rc;
fr.rcPage = rcPage;

// Non-Zero wParam means render, Zero means measure
Int32 wParam = (measureOnly ? 0 : 1);

// Allocate memory for the FORMATRANGE struct and
// copy the contents of our struct to this memory
IntPtr lParam = Marshal.AllocCoTaskMem( Marshal.SizeOf( fr ) );
Marshal.StructureToPtr(fr, lParam, false);

// Send the actual Win32 message
int res = SendMessage(RTB.Handle, EM_FORMATRANGE, wParam, lParam);

// Free allocated memory
Marshal.FreeCoTaskMem(lParam);

// and release the device context
g.ReleaseHdc(hdc);

g.Dispose();

return res;
}

// C#
/// <summary>
/// Convert between 1/100 inch (unit used by the .NET framework)
/// and twips (1/1440 inch, used by Win32 API calls)
/// </summary>
/// <param name="n">Value in 1/100 inch</param>
/// <returns>Value in twips</returns>
private Int32 HundredthInchToTwips(int n)
{
return (Int32)(n*14.4);
}
// C#
/// <summary>
/// Free cached data from rich edit control after printing
/// </summary>
public void FormatRangeDone(ref RichTextBox RTB)
{
IntPtr lParam = new IntPtr(0);
SendMessage(RTB.Handle, EM_FORMATRANGE, 0, lParam);
}

public void RTFtoPictureBox(ref RichTextBox RTB, ref PictureBox PB)
{
this.m_nFirstCharOnPage = 0;

do
{
this.m_nFirstCharOnPage = this.FormatRange(false, ref RTB, PB,
this.m_nFirstCharOnPage, RTB.Text.Length);
if(this.m_nFirstCharOnPage!= RTB.Text.Length)
{
PB.Height +=1;
this.m_nFirstCharOnPage = 0;
}
}
while(this.m_nFirstCharOnPage < RTB.Text.Length);

this.FormatRangeDone(ref RTB);

}

public void RTFtoBitmap(ref RichTextBox RTB, ref Bitmap b)
{
this.m_nFirstCharOnPage = 0;

do
{
this.m_nFirstCharOnPage = this.FormatRange(false, ref RTB, ref b,
this.m_nFirstCharOnPage, RTB.Text.Length);
if(this.m_nFirstCharOnPage!= RTB.Text.Length)
{
b = new Bitmap(b.Width, b.Height+1);
this.m_nFirstCharOnPage = 0;
}
}
while(this.m_nFirstCharOnPage < RTB.Text.Length);

this.FormatRangeDone(ref RTB);

}

}

By using ContentsResizedEventArgs of ContentsResized function, I can
obtain the content size of RichTextBox content and create a new bitmap.
The RTFtoBitmap method of RtfToPicture2 class is then called to export
the content of RichTextBox in WYSIWYG mode to the bitmap created
before.

The class works at most of the time but I find that sometimes the line
break in the bitmap is not exactly the same as that in the richtextbox.

Does anyone have idea how to fix the above problem?

Many Thanks,
Vincent