加载器 Loader

加载器Loader用来加载3D模型或其他文件，不同格式的模型使用不同的加载器。

所有加载器都继承自父类Loader

Loader的核心方法为load(url, onLoad, onProgress, onError)

• url - A string containing the path/URL of the model file.
• onLoad - (optional) A function to be called after the loading is successfully completed. The function receives the loaded Object3D as an argument.
• onProgress - (optional) A function to be called while the loading is in progress. The function receives a XMLHttpRequest instance, which contains total and loaded bytes.
• onError - (optional) A function to be called if an error occurs during loading. The function receives error as an argument.

加载管理器LoadingManager在构造加载器时被自动应用

加载管理器用于追踪和显示有关加载总体状态的信息，而不是处理已加载的数据

加载管理器的核心方法：onStart, onLoad, onProgress, onError

ThreeJS支持的加载器包括：