GLTF模型太暗

Question

尝试将此汽车模型加载到我的场景中，这是它在glTF Viewer中的外观：

我遵循了这个例子。使用这种更新的加载方法，模型仍然很暗，如果我尝试缩放或定位它，它会完全消失。

这是它的加载方式：

 const loader = new THREE.GLTFLoader();
const roughnessMipmapper = new RoughnessMipmapper( renderer );
loader.load( 'models/car_datsun/scene.gltf', function ( gltf ) { 
    gltf.scene.traverse( function (child) {
        if (child.isMesh) {
            roughnessMipmapper.generateMipmaps(child.material);
        }
        child.scale.set(0.5,0.5,0.5); //must comment this line out to appear 
        child.position.y += 10; //must comment this line out to appear
        child.position.z += 20; //must comment this line out to appear
    });
    scene.add(gltf.scene);
}, undefined, function ( error ) {
    console.error(error);
});
roughnessMipmapper.dispose();

我还有一盏灯，用来模拟太阳：

 const light = new THREE.DirectionalLight(0xffffff, 0.5);
 light.position.set(500,200,500); //looking at 0,0,0
 scene.add(light);

渲染器设置为使用sRGB：

renderer.outputEncoding = THREE.sRGBEncoding;