function optionalParameter ( value, defaultValue ) {

		return value !== undefined ? value : defaultValue;

	}
@author jbouny / https://github.com/jbouny

Work based on :
@author Slayvin / http://slayvin.net : Flat mirror for three.js
@author Stemkoski / http://www.adelphi.edu/~stemkoski : An implementation of water shader based on the flat mirror
@author Jonas Wagner / http://29a.ch/ && http://29a.ch/slides/2012/webglwater/ : Water shader explanations in WebGL