Bitmap bmp;
		Graphics g;

		public MainForm()
		{
			InitializeComponent();

			this.DoubleBuffered = true;

			this.MouseMove += new MouseEventHandler(mouseMove);
			bmp = new Bitmap(this.Width, this.Height);
			g = Graphics.FromImage(bmp);
		}

		protected override void OnPaint(PaintEventArgs e)
		{
			Point p = PointToClient(Cursor.Position);
			g.FillRectangle(Brushes.Black, new Rectangle(p.X,p.Y, 40, 40));
			e.Graphics.DrawImage(bmp, Point.Empty);
			g.Clear(Color.Transparent);
		}

		private void mouseMove(object sender, MouseEventArgs e)
		{
			this.Invalidate();
		}