xOf(callback),1)
				return;	
			}
			// make it grow
			mesh.scale.set(1,1,1).multiplyScalar( age2Scale(age) )
			// handle opacity
			material.opacity= age2Opacity(age)
		})
	}
	this.update	= function(delta, now){
		updateFcts.forEach(function(updateFct){
			updateFct(delta, now)
		})
	}
	function createTweenMidi(maxAge, attackTime, releaseTime){
		return function(age){
			if( age < attackTime ){
				return age / attackTime
			}else if( age < maxAge - releaseTime ){
				return 1;
			}else{
				return (max