StringGrid右击选中表格（右键点击也是MouseDown）

procedure TFGLGL.StringGrid1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var
    MousePos:   TSmallPoint;
begin
    if   Button   =   mbRight   then
    begin
        MousePos.x   :=   x;
        MousePos.y   :=   y;
        SendMessage(StringGrid1.Handle, WM_LBUTTONDOWN, 0, MAKELONG(x, y));
        SendMessage(StringGrid1.Handle, WM_LBUTTONUP, 0, MAKELONG(x, y));
    end;
end;