flex怎么实现百叶窗特效

package effects
{
    
    import effects.effectClasses.BlindsInstance;
    
    import mx.controls.scrollClasses.ScrollBarDirection;
    import mx.effects.IEffectInstance;
    import mx.effects.TweenEffect;
    
    public class Blinds extends TweenEffect
    {
        
        private static var AFFECTED_PROPERTIES:Array = ["mask"];
        
        public function Blinds(target:Object=null)
        {
            super(target);
            instanceClass = BlindsInstance;
        }
        
        public var direction:String = ScrollBarDirection.VERTICAL;
        
        public var blindsFrom:Number;
        
        public var blindsTo:Number;
        
        public var gapFrom:Number;
        
        public var gapTo:Number;
        
        override public function getAffectedProperties():Array
        {
            return AFFECTED_PROPERTIES;
        }
        
        override protected function initInstance(instance:IEffectInstance):void
        {
            super.initInstance(instance);
            var blindsInstance:BlindsInstance = BlindsInstance(instance);
            blindsInstance.direction = direction;
            blindsInstance.blindsFrom = blindsFrom;
            blindsInstance.blindsTo = blindsTo;
            blindsInstance.gapFrom = gapFrom;
            blindsInstance.gapTo = gapTo;
        }
        
    }
    
}