procedure TForm1.RichEdit1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
var
RE: TRichEdit;
Col, Row: Integer;
begin
RE := TRichEdit(Sender);
Row := RE.Perform(EM_LINEFROMCHAR, RE.SelStart, 0);
Col := RE.SelStart - RE.Perform(EM_LINEINDEX, Row, 0);
ShowMessage(Format('Linea: %d, Columna: %d',[Row, Col]));
end;