Extrascreen drawing

1. You can perform off-screen rendering using a Framebuffer Object.
2. You can save to a file by reading back the contents of the framebuffer with GL.ReadPixels, storing them to a System.Drawing.Bitmap and calling its Save() method. Check the source code for GLControl.GrabScreenshot() to find out how to do this - I have used this method to record 720p/30Hz video in realtime.

Edit: I have added documentation on how to save an OpenGL rendering to disk.

This is a video card limitation. Check MaxTextureSize with GL.GetInteger().