function addLine( a, b, hex ) {

		addPoint( a, hex );
		addPoint( b, hex );

	}
@author alteredq / http://alteredqualia.com/

	- shows frustum, line of sight and up of the camera
	- suitable for fast updates
	- based on frustum visualization in lightgl.js shadowmap example
		http://evanw.github.com/lightgl.js/tests/shadowmap.html