GetSurfaceLevel

  if( SUCCEEDED( g_pTexture->GetSurfaceLevel( 0, &pSurface) ) )
    {
        pd3dDevice->SetRenderTarget( 0, pSurfac );
        SAFE_RELEASE( pSurfac );
    }
GetSurfaceLevel这个是不是 把 一个surface和texture给关联起来了 
对那个suiface的修改 就是对texture的修改？

 SetRenderTarget 然后又把这个surface 设置到和 backbuffer关联 
所以 最后 屏幕显示的内容 被自动存进了 g_pTexture

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 mipmaps

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