Author: Jonas Bilinkevicius

I am currently trapping the OnMouseMove event, however have run into significant 
problems converting the mouse coordinates into a line and character offset in a 
rich edit.

Answer:
1   
2   procedure TForm1.RichEdit1MouseMove(Sender: TObject; Shift: TShiftState; X, Y:
3     Integer);
4   var
5     Point: TPoint;
6     Value: LongInt;
7     LineNumber: Integer;
8     LinePos: Integer;
9     Line: string;
10  begin
11    {Get absolute position of character beneath mouse}
12    Point.x := X;
13    Point.y := Y;
14    Value := RichEdit1.Perform(EM_CHARFROMPOS, 0, LParam(@Point));
15    if Value >= 0 then
16    begin
17      {Get line number}
18      LineNumber := RichEdit1.Perform(EM_LINEFROMCHAR, Value, 0);
19      {Get line position}
20      LinePos := Value - RichEdit1.Perform(EM_LINEINDEX, LineNumber, 0);
21      {Get line}
22      Line := RichEdit1.Lines[LineNumber];
23      Label1.Caption := Format('Line: %d Column: %d: %s', [LineNumber, LinePos, 
24  Line]);
25    end
26    else
27    begin
28      Label1.Caption := EmptyStr;
29    end;
30  end;


This only works for RichEdits.