/// <summary>
/// Calculate or render the contents of our RichTextBox for printing
/// </summary>
/// <param name="e">The PrintPageEventArgs object from the PrintPage event</param>
/// <param name="posIniChar">Index of first character to be printed</param>
/// <param name="posEndChar">Index of last character to be printed</param>
/// <returns>Index of last character that fitted on the page, plus 1</returns>
public int DoPrint(int posIniChar, int posEndChar, PrintPageEventArgs e)
{
// Fill in the FORMATRANGE struct
var fr = FORMATRANGE.Set(e, posIniChar, posEndChar);
// Allocate memory for the FORMATRANGE struct and copy this to the memory
IntPtr lParam = Marshal.AllocCoTaskMem(Marshal.SizeOf(fr));
Marshal.StructureToPtr(fr, lParam, false);
// Zero wParam means measure, non-zero wParam means render
Int32 wParam = (MeasureOnly ? 0 : 1);
// Measure to get end char index needed for call delegate before print
if (beforePagePrintDelegate != null && !MeasureOnly)
{
int nextIndex = SendMessage(richTextBox.Handle, EM_FORMATRANGE, 0, lParam);
beforePagePrintDelegate(posIniChar, nextIndex - 1, e);
}
// Send the Win32 message for printing
int res = SendMessage(richTextBox.Handle, EM_FORMATRANGE, wParam, lParam);
// Free allocated memory
Marshal.FreeCoTaskMem(lParam);
// Release the device context handle obtained by a previous call
e.Graphics.ReleaseHdc(fr.hdc);
return(res);
}
