flex Away3D 使用背景透明的贴图的教程

有时需要在舞台中添加一些背景透明的图片贴图，比如一些标志什么的。

package{
    import flash.display.Sprite;
    import flash.display.StageAlign;
    import flash.display.StageScaleMode;
    import flash.events.Event;
    import flash.events.MouseEvent;
     
    import away3d.containers.View3D;
    import away3d.controllers.HoverController;
    import away3d.entities.Mesh;
    import away3d.materials.TextureMaterial;
    import away3d.primitives.CubeGeometry;
    import away3d.primitives.PlaneGeometry;
    import away3d.utils.Cast;
     
    [SWF(frameRate="60", backgroundColor="#FFFFFF")]
    public class S5 extends Sprite {
         
        private  var _view3D:View3D;
        private var cameraController:HoverController;//360全景展示相机控制器
         
        //物体 图片（用作方块 的纹理 ）
        [Embed(source="assets/logo_f10.png")]
        private var logoClass:Class;
         
        //地板图片（用作地板的纹理 ）
        [Embed(source="assets/road.jpg")]
        private var floorClass:Class;
         
        //logo材质
        private var logoMaterial:TextureMaterial;
         
        //地板材质
        private var floorMaterial:TextureMaterial;
         
        private var _lastX:Number = 0;
        private var _lastY:Number = 0;
         
        public function S5() {
            initEngine();
            initMaterials();
            initObjects();
            initListeners();
        }
         
        /**
         * 初始化引擎
         */
        private function initEngine():void
        {
            stage.scaleMode = StageScaleMode.NO_SCALE;
            stage.align = StageAlign.TOP_LEFT;
             
            // 创建一个视口
            _view3D = new View3D();
            _view3D.antiAlias = 4; //设置抗锯齿级别
             
            //初始化摄像头
            cameraController = new HoverController(_view3D.camera);
            /*cameraController.distance = 1000;
            cameraController.minTiltAngle = 0;
            cameraController.maxTiltAngle = 90;
            cameraController.panAngle = 45;*/
            cameraController.tiltAngle = 15;
             
            addChild(_view3D);
        }
         
        /**
         * 初始化材质
         */
        private function initMaterials():void
        {
            //地板的纹理
            floorMaterial = new TextureMaterial(Cast.bitmapTexture(floorClass));
             
            //logo的纹理
            logoMaterial = new TextureMaterial(Cast.bitmapTexture(logoClass));
            logoMaterial.alpha = 1
            logoMaterial.alphaThreshold=0.5 //图片背景透明
        }
         
        /**
         * 初始化物体
         */
        private function initObjects():void
        {
            // 在三维舞台中创建一个方块（地板 ）
            var cube1:Mesh = new Mesh(new CubeGeometry(500, 20, 300), floorMaterial);
            _view3D.scene.addChild(cube1);
             
            // 在三维舞台中创建一个平面的logo           
            var logo:Mesh = new Mesh(new PlaneGeometry(128, 128), logoMaterial);
            //(logo.geometry as PlaneGeometry).doubleSided = true; //双面 贴图
            logo.y = 100;
            logo.rotationX = 90;
            logo.rotationZ = 180;
            _view3D.scene.addChild(logo);
        }
         
        /**
         * 初始化监听
         */
        private function initListeners():void
        {
            addEventListener(Event.ENTER_FRAME, _onEnterFrame);
            //鼠标事件监听
            stage.addEventListener(MouseEvent.MOUSE_DOWN, onMouseDown);
            stage.addEventListener(MouseEvent.MOUSE_UP, onMouseUp);
            stage.addEventListener(MouseEvent.MOUSE_WHEEL,onWheel);
            stage.addEventListener(Event.RESIZE, onResize);
            onResize();
        }
         
        /**
         * 渲染视图
         */
        private function _onEnterFrame(e:Event):void
        {
            //渲染视图
            _view3D.render();
        }
         
        /**
         * 使用舞台大小一直全屏
         */
        private function onResize(event:Event = null):void
        {
            _view3D.width = stage.stageWidth;
            _view3D.height = stage.stageHeight;
        }
         
        /**
         * 鼠标滚轮事件
         */
        private function onWheel(e:MouseEvent):void
        {
            if(e.delta > 0){
                if(cameraController.distance < 1000)
                    cameraController.distance += 100;
            }else{
                if(cameraController.distance > 600)
                    cameraController.distance -= 100;
            }
        }
         
        /**
         * 鼠标按下事件
         */
        private function onMouseDown(event:MouseEvent):void
        {
            _view3D.stage.addEventListener(MouseEvent.MOUSE_MOVE, mouseMoveHandler);
            _lastX = _view3D.mouseX;
            _lastY = _view3D.mouseY;
        }
         
        /**
         * 鼠标弹起事件
         */
        private function onMouseUp(event:MouseEvent):void
        {
            _view3D.stage.removeEventListener(MouseEvent.MOUSE_MOVE, mouseMoveHandler);
        }
         
        /**
         * 鼠标移动事件
         */
        private function mouseMoveHandler(event:MouseEvent):void
        {
            //移动摄像机
            var dx:Number = _view3D.mouseX - _lastX;
            var dy:Number = _view3D.mouseY - _lastY;
             
            cameraController.panAngle += dx;
            cameraController.tiltAngle += dy;
             
            _lastX = _view3D.mouseX;
            _lastY = _view3D.mouseY;
        }
    }
}