.overlay

1，在引用.overlay文件中的定义的layout 或者 layoutElement的时候要注意大小写。

2， //   注释难道要写在空行里

初始化.overlay文件失败时，要注意在调用initialiseAllResourceGroups()的位置，是否在setDefaultNumMipmaps()的后面

Before we initialize the resources, we should also set the default number of mipmaps that textures use. We must set that before we initialize the resources for it to have any effect.

Add the following code to BasicTutorial6::go:

// Set default mipmap level (NB some APIs ignore this)
Ogre::TextureManager::getSingleton().setDefaultNumMipmaps(5);
// initialise all resource groups
Ogre::ResourceGroupManager::getSingleton().initialiseAllResourceGroups();

The application now has all resource groups initialized and ready to be used.