public BlackForm(Form parentForm)
{
InitializeComponent();
_parentForm = parentForm;
// set location & size to primary screen to reduce flicker while starting
this.Location = new Point(Screen.PrimaryScreen.Bounds.X, Screen.PrimaryScreen.Bounds.Y);
this.Size = new Size(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
}