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Step 3. Support QueryInterface

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[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

To expose the filter's new interfaces to clients, do the following:

  • Include the DECLARE_IUNKNOWN macro in the public declaration section of your filter:

    public:
    DECLARE_IUNKNOWN;

  • Override CUnknown::NonDelegatingQueryInterface to check for the IIDs of the two interfaces:

    STDMETHODIMP CGrayFilter::NonDelegatingQueryInterface(REFIID riid, void **ppv)
{
    if (riid == IID_ISpecifyPropertyPages)
    {
        return GetInterface(
           static_cast<ISpecifyPropertyPages*>(this),
           ppv);
    }
    else if (riid == IID_ISaturation)
    {
        return GetInterface(static_cast<ISaturation*>(this), ppv);
    }
    else
    {
        // Call the parent class.
        return CBaseFilter::NonDelegatingQueryInterface(riid, ppv);

        // NOTE: This example assumes that the filter inherits directly
        // from CBaseFilter. If your filter inherits from another class,
        // call the NonDelegatingQueryInterface method of that class.
    }
}

Next: Step 4. Create the Property Page.

Creating a Filter Property Page

How to Implement IUnknown