C#

public class MyPlot : Control {
   private Bitmap _buffer;

   public MyPlot() {
      ClearBuffer();
   }

   private void ClearBuffer() {
      _buffer = new Bitmap(base.Size);
      this.Invalidate();
   }

   protected override OnResize(EventArgs ea) {
      //Note that resizing the control will clear its content
      //if this should not occur that copying will be required
      ClearBuffer();
   }

   protected override OnPaint(PaintEventArgs pea) {
      if (_buffer != null)
         pea.Graphics.DrawImageUnscaled(0, 0, _buffer);
   }

   public void DrawCommand(string[] commands) {
      //Getting the Graphics object is a rather heavy operation
      //so dont do it for each single command
      using (Graphics g = Graphics.FromImage(_buffer)) {
         for (int i = 0; i < command.Length; i++) {
            DrawCommand(commands[i], g);
         }
      }
   }

   private void DrawCommand(string commands, Graphics g) {
      //some magic code here to determine what to do, e.g.
      g.DrawLine(Pens.Black, 5, 5, 10, 10);
      //or
      g.FillRectangle(Brushes.Red, 8, 17, 15, 20);
   }
}