tClearColor('skyblue',1)
	
	// init sprite material
	var texture	= THREE.ImageUtils.loadTexture('images/cloud10.png')
	var material	= new THREE.SpriteMaterial({
		map			: texture,
		useScreenCoordinates	: false,
	})
	material.color.set('grey')

	// spread uniform layer of cloud
	var centerClouds= new THREE.Vector3( 0, -1.0, -6)
	var rangeClouds	= new THREE.Vector3(20,  0.2, 16)
	var range	= new THREE.Vector3( 4,  0.1,  2)

	var nClusters	= 30
	var center	= new THREE.Vector3()
	for(var i = 0; i < nClusters; 