[]3D灯光阴影无效

var directionLight:DirectionLight = scene.addChild(new DirectionLight()) as DirectionLight;
directionLight.ambientColor = new Vector3(0.7, 0.6, 0.6);
directionLight.specularColor = new Vector3(1.0, 1.0, 0.9);
directionLight.diffuseColor = new Vector3(1, 1, 1);
directionLight.transform.position = new Vector3(0, 30, 0);  //这一行不管有没有，都一样没有效果
directionLight.direction = new Vector3(0, -1.0, -1.0);
directionLight.shadow = true;

var QiPanMesh:MeshSprite3D = new MeshSprite3D(Mesh.load("qipan/qipan-qipan.lm"), "qipan");
QiPanMesh.transform.position = new Vector3(0, 0, -1);
QiPanMesh.transform.rotation = new Quaternion(-1, 0, 0, 1);
QiPanMesh.layer = Layer.getLayerByNumber(5);
QiPanMesh.meshRender.castShadow = true;
QiPanMesh.meshRender.receiveShadow = true;
scene.addChild(QiPanMesh);

var gTitleMesh:MeshSprite3D = new MeshSprite3D(Mesh.load("gTitle/gTitle-Text001.lm"), "gTitle");
gTitleMesh.transform.position = new Vector3(0, 2, -60);
gTitleMesh.transform.rotation = new Quaternion(0, 0, 0, 1);
gTitleMesh.layer = Layer.getLayerByNumber(5);
gTitleMesh.meshRender.castShadow = true;
gTitleMesh.meshRender.receiveShadow = true;
scene.addChild(gTitleMesh);
 
注：其他都显示无误，就是阴影死活没有。