libGDX错误地渲染PNG透明度

Sample

我已添加 BlendingAttribute 但一些(并非所有)纹理仍然渲染不正确。这些尖面应该是透明的。以下是我的片段:

private void doneLoading() {

    terrain = assets.get("xx.g3db", Model.class);
    terrainInstance = new ModelInstance(terrain);
    for(n = 2; n < terrainInstance.materials.size; n++){
        terrainInstance.materials.get(n).set(new BlendingAttribute(GL30.GL_SRC_ALPHA, GL30.GL_ONE_MINUS_SRC_ALPHA)); // this should working for all faces
    }
    instances.add(terrainInstance);
    loading = false;
}

@Override
public void render() {
    if (loading && assets.update()) {
        doneLoading();
    }
    personcam.update(Gdx.graphics.getDeltaTime());

    Gdx.gl.glViewport(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
    Gdx.gl.glTexParameteri(GL30.GL_TEXTURE_2D, GL30.GL_TEXTURE_MAG_FILTER, GL30.GL_NEAREST);
    Gdx.gl.glClearColor(1, 1, 1, 1);
    Gdx.gl.glClear(GL30.GL_COLOR_BUFFER_BIT | GL30.GL_DEPTH_BUFFER_BIT);

    modelBatch.begin(cam);
    modelBatch.render(instances, environment);
    modelBatch.end();

}

我已经检查了我的纹理文件,它们很好。我的FBX文件(我正在使用SketchUp 8)也很好。为什么有些面不能正确渲染透明度?这是臭虫吗?