有些時候,應用程序需要枚舉graph中的filter或者是枚舉filter所支持的pin。因此directshow提供了枚舉graph filter中的com組件方法。
1、枚舉filter
Filter圖表管理器支持IFilterGraph::EnumFilters方法,來枚舉graph圖中的所有的filter。他返回一個IEnumFilters接口,利用這個接口就可以遍歷graph中的所有的filter。
下面的代碼演示了,如何遍歷graph中的filter,並且顯示filter的名字。
HRESULT EnumFilters (IFilterGraph *pGraph) { IEnumFilters *pEnum = NULL; IBaseFilter *pFilter; ULONG cFetched; HRESULT hr = pGraph->EnumFilters(&pEnum); if (FAILED(hr)) return hr; while(pEnum->Next(1, &pFilter, &cFetched) == S_OK) { FILTER_INFO FilterInfo; hr = pFilter->QueryFilterInfo(&FilterInfo); if (FAILED(hr)) { MessageBox(NULL, TEXT("Could not get the filter info"),TEXT("Error"), MB_OK | MB_ICONERROR); continue; // Maybe the next one will work. } #ifdef UNICODE MessageBox(NULL, FilterInfo.achName, TEXT("Filter Name"), MB_OK); #else char szName[MAX_FILTER_NAME]; int cch = WideCharToMultiByte(CP_ACP, 0, FilterInfo.achName,MAX_FILTER_NAME, szName, MAX_FILTER_NAME, 0, 0); if (chh > 0) MessageBox(NULL, szName, TEXT("Filter Name"), MB_OK); #endif // The FILTER_INFO structure holds a pointer to the Filter Graph // Manager, with a reference count that must be released. if (FilterInfo.pGraph != NULL) { FilterInfo.pGraph->Release(); } pFilter->Release(); } pEnum->Release(); return S_OK; } |
2、枚舉pin
Filter支持IBaseFilter::EnumPins方法,這個方法可以可以枚舉filter所有的pin。它返回一個IEnumPins接口,IEnumPins::Next可以遍歷pin的接口。
下面的代碼演示瞭如何如何查找一個輸出和輸入pin。利用PIN_DIRECTION參數來制定pin的類型(輸入還是輸出)。
HRESULT GetPin(IBaseFilter *pFilter, PIN_DIRECTION PinDir, IPin **ppPin) { IEnumPins *pEnum = NULL; IPin *pPin = NULL; HRESULT hr; if (ppPin == NULL) { return E_POINTER; } hr = pFilter->EnumPins(&pEnum); if (FAILED(hr)) { return hr; } while(pEnum->Next(1, &pPin, 0) == S_OK) { PIN_DIRECTION PinDirThis; hr = pPin->QueryDirection(&PinDirThis); if (FAILED(hr)) { pPin->Release(); pEnum->Release(); return hr; } if (PinDir == PinDirThis) //如果類型符合 { // Found a match. Return the IPin pointer to the caller. **ppPin = pPin; pEnum->Release(); return S_OK; } // Release the pin for the next time through the loop. pPin->Release(); } // No more pins. We did not find a match. pEnum->Release(); return E_FAIL; } |
利用這個方法可以很容易的就查找一個pin,然後調用IPin::ConnectedTo方法確定這個pin是否被連接,可以查找一個空閒的pin。