function RE_GetLastVisibleLine(RichEdit: TRichEdit): Integer;
 const
  EM_EXLINEFROMCHAR = WM_USER + 54;
 var
  r: TRect;
  i: Integer;
 begin
  {
  The EM_GETRECT message retrieves the formatting rectangle
  of an edit control.
 }
  RichEdit.Perform(EM_GETRECT, 0, Longint(@r));
  r.Left := r.Left + 1;
  r. := r.Bottom - 2;
  {
  The EM_CHARFROMPOS message retrieves information about the character
  closest to a specified point in the client area of an edit control
 }
  i := RichEdit.Perform(EM_CHARFROMPOS, 0, Integer(@r.topleft));
  {
  The EM_EXLINEFROMCHAR message determines which
  line contains the specified character in a rich edit control
 }
  Result := RichEdit.Perform(EM_EXLINEFROMCHAR, 0, i);
 end;
 {
 Sending the EM_GETFIRSTVISIBLELINE message to a multi-line edit control
 finds out which line is the first line visible.
 This is the line that is currently displayed at the top of the control.
}
 function RE_GetFirstVisibleLine(RichEdit: TRichEdit): Integer;
 begin
  Result := RichEdit.Perform(EM_GETFIRSTVISIBLELINE, 0, 0);
 end;