版本为2.7.1，无法背景透明，永远是黑色
export default class GameUI extends Laya.Scene {
    constructor() {
        super();

        Config.isAlpha = true;
       Laya.init(480, 900);
       Laya.stage.bgColor = null;

        //加载场景文件
        this.loadScene("test/TestScene.scene");

        //添加3D场景
        var scene = Laya.stage.addChild(new Laya.Scene3D());

        //添加照相机
        var camera = (scene.addChild(new Laya.Camera(0, 0.1, 100)));
        camera.transform.translate(new Laya.Vector3(0, 3, 3));
        camera.transform.rotate(new Laya.Vector3(-30, 0, 0), true, false);
        camera.clearColor=null; 

        //添加方向光
        var directionLight = scene.addChild(new Laya.DirectionLight());
        directionLight.color = new Laya.Vector3(0.6, 0.6, 0.6);
        directionLight.transform.worldMatrix.setForward(new Laya.Vector3(1, -1, 0));

        //添加自定义模型
        var box = scene.addChild(new Laya.MeshSprite3D(Laya.PrimitiveMesh.createBox(1, 1, 1)));
        box.transform.rotate(new Laya.Vector3(0, 45, 0), false, false);
        var material = new Laya.BlinnPhongMaterial();
		Laya.Texture2D.load("res/layabox.png", Laya.Handler.create(null, function(tex) {
				material.albedoTexture = tex;
		}));
        box.meshRenderer.material = material;
    }
}
附件：
laya1.rar
laya1.rar