IDirect3DDevice9::GetBackBuffer参数如何使用

DirectX初学

HRESULT GetBackBuffer(UINT iSwapChain,
    UINT BackBuffer,
    D3DBACKBUFFER_TYPE Type,
    IDirect3DSurface9 **ppBackBuffer
);


第一个参数以什么值来传递？

iSwapChain
[in] An unsigned integer specifying the swap chain

BackBuffer
[in] Index of the back buffer object to return. Back buffers are numbered from 0 to the total number of back buffers minus one. A value of 0 returns the first back buffer, not the front buffer. The front buffer is not accessible through this method. Use IDirect3DDevice9::GetFrontBufferData to retrieve a copy of the front buffer.

Type
[in] Stereo view is not supported in Microsoft DirectX 9.0, so the only valid value for this parameter is D3DBACKBUFFER_TYPE_MONO

第一个参数文档没说明
第二个参数说的很不详细
Back buffers are numbered from 0 to the total number of back buffers minus one.到底有几个BackBuffer?

hr = g_pDevice->GetBackBuffer(怎么写,怎么写,D3DBACKBUFFER_TYPE_MONO,&g_pBackBuffer);

DirectX初学

我刚才用0来传送，结果调用成功，
于是我再:

hr = g_pDevice->GetBackBuffer(0,0,D3DBACKBUFFER_TYPE_MONO,&g_pBackBuffer);
        if(hr == D3D_OK)
                MessageBox(hwnd,L"OK",0,0);
hr = g_pDevice->GetBackBuffer(0,1,D3DBACKBUFFER_TYPE_MONO,&g_pBackBuffer2);
        if(hr == D3D_OK)
                MessageBox(hwnd,L"OK",0,0);
hr = g_pDevice->GetBackBuffer(0,2,D3DBACKBUFFER_TYPE_MONO,&g_pBackBuffer3);
        if(hr == D3D_OK)
                MessageBox(hwnd,L"OK",0,0);

hr = g_pDevice->GetBackBuffer(0,3,D3DBACKBUFFER_TYPE_MONO,&g_pBackBuffer4);
           if(hr == D3D_OK)
                MessageBox(hwnd,L"OK",0,0);

它打印了三次对话框，。。这是怎么回事？怎么有三个BackBuffer,我初学者。实在不理解。
请高手指点

DirectX初学

唉呀！头搞晕了。
上面我说怎么出现了三个对话框出来呢？
原来是这行 ddp.BackBufferCount = 3；
初初学Direct3D。一时出来许多问题。而一时又解决不了。搞到最后头乱乱的。
大家多多指点！！！