Criar Check Box na Grid

procedure TForm1.DBGrid1DrawColumnCell(Sender: TObject; const Rect: TRect; DataCol: Integer; Column: TColumn; State: TGridDrawState);
var
Check: Integer;
R: TRect;
begin
//Desenha um checkbox no dbgrid
if Column.FieldName = ATIVO then begin
DBGrid1.Canvas.FillRect(Rect);
Check := 0;
if ClientDataSet1Ativo.AsString = X then
Check := DFCS_CHECKED
else Check := 0;
R:=Rect;
InflateRect(R,-2,-2); {Diminue o tamanho do CheckBox}
DrawFrameControl(DBGrid1.Canvas.Handle,R,DFC_BUTTON, DFCS_BUTTONCHECK or Check);
end;
end;