Option Explicit On 

Imports System
Imports System.Windows.Forms
Imports System.Drawing
Imports System.Runtime.InteropServices
Imports System.Drawing.Printing

Namespace RichTextBoxPrintCtrl
   Public Class RichTextBoxPrintCtrl
      Inherits RichTextBox
      ' Convert the unit that is used by the .NET framework (1/100 inch) 
      ' and the unit that is used by Win32 API calls (twips 1/1440 inch)
      Private Const AnInch As Double = 14.4

      <StructLayout(LayoutKind.Sequential)> _
       Private Structure RECT
         Public Left As Integer
         Public Top As Integer
         Public Right As Integer
         Public Bottom As Integer
      End Structure

      <StructLayout(LayoutKind.Sequential)> _
      Private Structure CHARRANGE
         Public cpMin As Integer          ' First character of range (0 for start of doc)
         Public cpMax As Integer          ' Last character of range (-1 for end of doc)
      End Structure

      <StructLayout(LayoutKind.Sequential)> _
      Private Structure FORMATRANGE
         Public hdc As IntPtr             ' Actual DC to draw on
         Public hdcTarget As IntPtr       ' Target DC for determining text formatting
         Public rc As Rect                ' Region of the DC to draw to (in twips)
         Public rcPage As Rect            ' Region of the whole DC (page size) (in twips)
         Public chrg As CHARRANGE         ' Range of text to draw (see above declaration)
      End Structure

      Private Const WM_USER As Integer = &H400
      Private Const EM_FORMATRANGE As Integer = WM_USER + 57

      Private Declare Function SendMessage Lib "USER32" Alias "SendMessageA" (ByVal hWnd As IntPtr, ByVal msg As Integer, ByVal wp As IntPtr, ByVal lp As IntPtr) As IntPtr

      ' Render the contents of the RichTextBox for printing
      '	Return the last character printed + 1 (printing start from this point for next page)
      Public Function Print(ByVal charFrom As Integer, ByVal charTo As Integer, ByVal e As PrintPageEventArgs) As Integer

         ' Mark starting and ending character 
         Dim cRange As CHARRANGE
         cRange.cpMin = charFrom
         cRange.cpMax = charTo

         ' Calculate the area to render and print
         Dim rectToPrint As RECT
         rectToPrint.Top = e.MarginBounds.Top * AnInch
         rectToPrint.Bottom = e.MarginBounds.Bottom * AnInch
         rectToPrint.Left = e.MarginBounds.Left * AnInch
         rectToPrint.Right = e.MarginBounds.Right * AnInch

         ' Calculate the size of the page
         Dim rectPage As RECT
         rectPage.Top = e.PageBounds.Top * AnInch
         rectPage.Bottom = e.PageBounds.Bottom * AnInch
         rectPage.Left = e.PageBounds.Left * AnInch
         rectPage.Right = e.PageBounds.Right * AnInch

         Dim hdc As IntPtr = e.Graphics.GetHdc()

         Dim fmtRange As FORMATRANGE
         fmtRange.chrg = cRange                 ' Indicate character from to character to 
         fmtRange.hdc = hdc                     ' Use the same DC for measuring and rendering
         fmtRange.hdcTarget = hdc               ' Point at printer hDC
         fmtRange.rc = rectToPrint              ' Indicate the area on page to print
         fmtRange.rcPage = rectPage             ' Indicate whole size of page

         Dim res As IntPtr = IntPtr.Zero          

         Dim wparam As IntPtr = IntPtr.Zero
         wparam = New IntPtr(1)

         ' Move the pointer to the FORMATRANGE structure in memory
         Dim lparam As IntPtr = IntPtr.Zero
         lparam = Marshal.AllocCoTaskMem(Marshal.SizeOf(fmtRange))
         Marshal.StructureToPtr(fmtRange, lparam, False)

         ' Send the rendered data for printing 
         res = SendMessage(Handle, EM_FORMATRANGE, wparam, lparam)

         ' Free the block of memory allocated
         Marshal.FreeCoTaskMem(lparam)

         ' Release the device context handle obtained by a previous call
         e.Graphics.ReleaseHdc(hdc)

         ' Return last + 1 character printer
         Return res.ToInt32()
      End Function

   End Class
End Namespace