Parameters
Level [in]
UINT
Identifies a level of the texture
resource. This method returns a surface for the level specified by this
parameter. The top-level surface is denoted by 0.
ppSurfaceLevel [out]
IDirect3DSurface9
Address of a pointer to an
IDirect3DSurface9 interface, representing the returned surface.
这个猜想对不对呢
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texture里面有surface这个结构
用于 mipmap 或者cubetexture
一个texture里面有很多surface 用level 来标识
得到了其中一个的指针 指定给render target我那么理解差不多是那个意思
原文：http://www.cnblogs.com/minggoddess/p/3567251.html