c++ - 双指针函数参数和 CComPtr

Question

我不确定这种在函数内部使用 CComPtr 的方式，该函数的参数表示为双指针:

HRESULT D3DPresentEngine::CreateD3DSample(
    IDirect3DSwapChain9 *pSwapChain, 
    IMFSample **ppVideoSample
    )
{
    // Caller holds the object lock.

    D3DCOLOR clrBlack = D3DCOLOR_ARGB(0xFF, 0x00, 0x00, 0x00);

    CComPtr< IDirect3DSurface9 > pSurface;
    CComPtr< IMFSample > pSample;

    // Get the back buffer surface.
    ReturnIfFail( pSwapChain->GetBackBuffer(0, D3DBACKBUFFER_TYPE_MONO, &pSurface ) );

    // Fill it with black.
    ReturnIfFail( m_pDevice->ColorFill(pSurface, NULL, clrBlack));

    // Create the sample.
    ReturnIfFail( MFCreateVideoSampleFromSurface(pSurface, &pSample));

    // Return the pointer to the caller.
    *ppVideoSample = pSample;
    (*ppVideoSample)->AddRef();

    return S_OK;
}

我对最后一次赋值 + AddRef 调用有疑问。

它们适合你吗？

提前致谢

Answer 1

没关系，但可以简化:

HRESULT D3DPresentEngine::CreateD3DSample(
    IDirect3DSwapChain9 *pSwapChain, 
    IMFSample **ppVideoSample
    )
{
    // Caller holds the object lock.

    D3DCOLOR clrBlack = D3DCOLOR_ARGB(0xFF, 0x00, 0x00, 0x00);

    CComPtr< IDirect3DSurface9 > pSurface;

    // Get the back buffer surface.
    ReturnIfFail( pSwapChain->GetBackBuffer(0, D3DBACKBUFFER_TYPE_MONO, &pSurface ) );

    // Fill it with black.
    ReturnIfFail( m_pDevice->ColorFill(pSurface, NULL, clrBlack));

    // Create the sample.
    ReturnIfFail( MFCreateVideoSampleFromSurface(pSurface, ppVideoSample));

    return S_OK;
}

在您的代码中，AddRef 是必需的，因为 pSample 在超出范围时将Release。