Javascript 脸没有背

我有这样的密码：

var roofGeometry = new THREE.Geometry();

roofGeometry.vertices.push(
    new THREE.Vector3(-0.5, 0, 0.5),
    new THREE.Vector3(0.5, 0, 0.5),
    new THREE.Vector3(0, 1, 0.5),
    new THREE.Vector3(0.5, 0, -0.5),
    new THREE.Vector3(0, 1, -0.5),
    new THREE.Vector3(-0.5, 0, -0.5)
);
roofGeometry.faces.push(
    new THREE.Face3(0, 1, 2),
    //new THREE.Face4(1, 3, 4, 2),
    new THREE.Face3(5, 3, 4)/*,
    new THREE.Face4(0, 5, 4, 2)*/
);
//...

---

为什么旋转三角形时三角形消失了？

在材质中使用

侧面：三。双面

可能的重复：