private void opend3dcube_Click(object sender, EventArgs e)
{
if (!form_3DcuboidA.Visible)
{
//form_3DcuboidA = null;
form_3DcuboidA.Refresh();
form_3DcuboidA.Text += " A";
BackgroundWorker backgroundWorkerA = new BackgroundWorker();
backgroundWorkerA.DoWork += new DoWorkEventHandler(delegate { form_3DcuboidA.ShowDialog(); });
backgroundWorkerA.RunWorkerAsync();
}
}