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Implementing CEcho::FinalConstruct

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[The feature associated with this page, Windows Media Player SDK, is a legacy feature. It has been superseded by MediaPlayer. MediaPlayer has been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer instead of Windows Media Player SDK, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The CEcho::FinalConstruct method is implemented in Echo.cpp. It contains code to read the property values from the registry when Windows Media Player instantiates the DSP plug-in object. This is important because it allows the user settings to persist between instances of the object, as well as between sessions. The plug-in wizard sample code provides implementation to read a single property from the registry. You can modify this code to handle the delay time property, and then add code to read the wet mix property value.

The following example code reads each property value from the registry and stores each in the correct member variable:

CRegKey key;
LONG    lResult;
DWORD   dwValue;

lResult = key.Open(HKEY_CURRENT_USER, kszPrefsRegKey, KEY_READ);
if (ERROR_SUCCESS == lResult)
{
    // Read the delay time from the registry. 
    lResult = key.QueryValue(dwValue, kszPrefsDelayTime );
    if (ERROR_SUCCESS == lResult)
    {
        m_dwDelayTime = dwValue;
    }

    // Read the wet mix value from the registry. 
    lResult = key.QueryValue(dwValue, kszPrefsWetmix );
    if (ERROR_SUCCESS == lResult)
    {
        // Convert the DWORD to a double.
        m_fWetMix = (double)dwValue / 100;
        // Calculate the dry mix value.
        m_fDryMix = 1.0 - m_fWetMix;
    }

}

return S_OK;

Notice that the DWORD value for the wet mix is converted to a floating-point value. Also note that the code calculates the correct value for m_fDryMix.

Modifying the Echo Sample Property Page