OnDrawColumnCell: Centralizar

procedure TFrm1.DBGridDrawColumnCell(Sender: TObject; const Rect: TRect; 
  DataCol: Integer; Column: TColumn; State: TGridDrawState); 
var 
  S: string; 
  R: TRect; 
begin 
  if (VAlor < 0)then 
  begin 
    with DBGrid.Canvas do 
    begin 
      Font.Color  := clRed; 
      FillRect(Rect); 

      S := Column.Field.AsString; 
      R := Rect; 
      DrawText(Handle, PChar(S), Length(S), R, DT_CENTER or DT_VCENTER); 
    end; 
  end; 
end;