Find an Unconnected Pin on a Filter

    在典型的DirectShow图形构建场景中，您需要一个与特定引脚方向（输入或输出）匹配的未连接引脚。 例如，当连接两个滤波器时，可以将一个滤波器的输出引脚连接到另一个滤波器的输入引脚。 在连接它们之前，两个引脚必须断开。
   首先，我们需要一个测试引脚是否连接到另一个引脚的函数。 该函数调用IPin :: ConnectedTo方法来测试引脚是否连接到另一个引脚。// Query whether a pin is connected to another pin.
//
// Note: This function does not return a pointer to the connected pin.

HRESULT IsPinConnected(IPin *pPin, BOOL *pResult)
{
IPin *pTmp = NULL;
HRESULT hr = pPin->ConnectedTo(&pTmp);
if (SUCCEEDED(hr))
{
*pResult = TRUE;
}
else if (hr == VFW_E_NOT_CONNECTED)
{
// The pin is not connected. This is not an error for our purposes.
*pResult = FALSE;
hr = S_OK;
}

SafeRelease(&pTmp);
return hr;
}   接下来，我们需要一个测试引脚是否与指定引脚方向匹配的函数。 该函数调用IPin :: QueryDirection方法来获取引脚方向。// Query whether a pin has a specified direction (input / output)
HRESULT IsPinDirection(IPin *pPin, PIN_DIRECTION dir, BOOL *pResult)
{
PIN_DIRECTION pinDir;
HRESULT hr = pPin->QueryDirection(&pinDir);
if (SUCCEEDED(hr))
{
*pResult = (pinDir == dir);
}
return hr;
}   下一个功能通过两个标准（引脚方向和连接状态）来匹配引脚。// Match a pin by pin direction and connection state.
HRESULT MatchPin(IPin *pPin, PIN_DIRECTION direction, BOOL bShouldBeConnected, BOOL *pResult)
{
assert(pResult != NULL);

BOOL bMatch = FALSE;
BOOL bIsConnected = FALSE;

HRESULT hr = IsPinConnected(pPin, &bIsConnected);
if (SUCCEEDED(hr))
{
if (bIsConnected == bShouldBeConnected)
{
hr = IsPinDirection(pPin, direction, &bMatch);
}
}

if (SUCCEEDED(hr))
{
*pResult = bMatch;
}
return hr;
}   最后，下面的函数使用IEnumPins接口来遍历过滤器上的引脚。 调用者指定所需的引脚方向。 对于每个引脚，函数调用MatchPin来测试引脚是否匹配。 如果方向匹配并且引脚未连接，则该函数返回指向ppPin参数中匹配引脚的指针。// Return the first unconnected input pin or output pin.
HRESULT FindUnconnectedPin(IBaseFilter *pFilter, PIN_DIRECTION PinDir, IPin **ppPin)
{
IEnumPins *pEnum = NULL;
IPin *pPin = NULL;
BOOL bFound = FALSE;

HRESULT hr = pFilter->EnumPins(&pEnum);
if (FAILED(hr))
{
goto done;
}

while (S_OK == pEnum->Next(1, &pPin, NULL))
{
hr = MatchPin(pPin, PinDir, FALSE, &bFound);
if (FAILED(hr))
{
goto done;
}
if (bFound)
{
*ppPin = pPin;
(*ppPin)->AddRef();
break;
}
SafeRelease(&pPin);
}

if (!bFound)
{
hr = VFW_E_NOT_FOUND;
}

done:
SafeRelease(&pPin);
SafeRelease(&pEnum);
return hr;
}