如何使用DirectShow API捕获除捕获应用程序之外的桌面位图？

CoInitialize(NULL);
IGraphBuilder* pGraphBuilder = NULL;
CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void**)&pGraphBuilder);

ISampleGrabber* pSampleGrabber = NULL;
CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER, IID_ISampleGrabber, (void**)&pSampleGrabber);

pGraphBuilder->AddFilter(pSampleGrabber, L"Sample Grabber");

AM_MEDIA_TYPE mt;
ZeroMemory(&mt, sizeof(AM_MEDIA_TYPE));
mt.majortype = MEDIATYPE_Video;
mt.subtype = MEDIASUBTYPE_RGB24;
pSampleGrabber->SetMediaType(&mt);
pSampleGrabber->SetCallback(new SampleGrabberCallback(), 1);

ICreateDevEnum* pDevEnum = NULL;
CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER, IID_ICreateDevEnum, (void**)&pDevEnum);

IEnumMoniker* pEnumMoniker = NULL;
pDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory, &pEnumMoniker, 0);

IMoniker* pMoniker = NULL;
pEnumMoniker->Next(1, &pMoniker, NULL);

IBaseFilter* pVideoSource = NULL;
pMoniker->BindToObject(NULL, NULL, IID_IBaseFilter, (void**)&pVideoSource);

pGraphBuilder->AddFilter(pVideoSource, L"Video Source");

pGraphBuilder->ConnectDirect(GetPin(pVideoSource, PINDIR_OUTPUT), GetPin(pSampleGrabber, PINDIR_INPUT));
pGraphBuilder->ConnectDirect(GetPin(pSampleGrabber, PINDIR_OUTPUT), GetPin(pRenderer, PINDIR_INPUT));

IMediaControl* pMediaControl = NULL;
pGraphBuilder->QueryInterface(IID_IMediaControl, (void**)&pMediaControl);
pMediaControl->Run();

class SampleGrabberCallback : public ISampleGrabberCB
{
public:
    STDMETHODIMP_(ULONG) AddRef() { return 1; }
    STDMETHODIMP_(ULONG) Release() { return 2; }
    STDMETHODIMP QueryInterface(REFIID riid, void** ppv)
    {
        if (riid == IID_ISampleGrabberCB || riid == IID_IUnknown)
        {
            *ppv = (void*)this;
            return NOERROR;
        }
        return E_NOINTERFACE;
    }

    STDMETHODIMP SampleCB(double SampleTime, IMediaSample* pSample)
    {
        // 处理捕获到的位图数据
        return S_OK;
    }

    STDMETHODIMP BufferCB(double SampleTime, BYTE* pBuffer, long BufferLen)
    {
        // 处理捕获到的位图数据
        return S_OK;
    }
};