[ActionScript] AS3代码实现曝光过度效果

package 
{
    import flash.display.Loader;
    import flash.display.SimpleButton;
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.events.MouseEvent;
    import flash.geom.ColorTransform;
    import flash.net.URLRequest;
    
    /**
     * ...
     * @author FrostYen
     */
    public class ColorTransformExample extends Sprite
    {
        private var _ldr:Loader = new Loader();
        private var _sp:Sprite = new Sprite();
        private var _btn:Sprite = new Sprite();
        private var _colorTransform:ColorTransform = new ColorTransform(1, 1, 1, 1, 255, 255, 255, 0);
        private var _frame:int=15;//相当于影片剪辑动画的帧数
        public function ColorTransformExample() {
            
            _ldr.load(new URLRequest("image/farewell-to-fall.jpg"));
            _sp.transform.colorTransform = _colorTransform;
            
            _btn.graphics.beginFill(0x666666);
            _btn.graphics.drawRect(0, 0, 100, 50);
            _btn.graphics.endFill();
            _btn.buttonMode = true;
            _btn.x = 700;
            _btn.y = 100;

            this.addChild(_btn);
            this.addChild(_sp);
            _sp.addChild(_ldr);
            stage.frameRate = 36;//帧频
            
            _ldr.contentLoaderInfo.addEventListener(Event.COMPLETE, onImageLoaded);
            _btn.addEventListener(MouseEvent.CLICK, onClick);
        }
        
        private function onClick(e:MouseEvent):void 
        {
            addEventListener(Event.ENTER_FRAME, onEnter);
        }
        
        private function onEnter(e:Event):void 
        {
            if (_colorTransform.redOffset > 0) {
                _colorTransform.redOffset -= 255/_frame;
                _colorTransform.greenOffset -= 255/_frame;
                _colorTransform.blueOffset -= 255/_frame;
                _sp.transform.colorTransform = _colorTransform;
            }else {
                _colorTransform = new ColorTransform(1, 1, 1, 1, 255, 255, 255, 0);
                removeEventListener(Event.ENTER_FRAME, onEnter);
            }
        }
        
        private function onImageLoaded(e:Event):void 
        {
            
        }
    }
    
}