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COM interface classes in DirectShow fall into two groups: object creation and interface implementation. Class factory classes are provided for object creation, and other classes are provided to implement existing COM interfaces.
The COM utility classes include the following:
The following illustration shows the relationship between the COM classes and the interfaces they implement.
CClassFactoryand CFactoryTemplateare implemented by the base classes to handle automatic instantiation of filters, pins, and other DirectShow COM objects. These classes provide a scaffolding for object construction which wraps the actual COM elements required to construct an object.
CClassFactory, located in dllentry.cpp, inherits from CBaseObjectand implements the COM IClassFactoryinterface. This interface is used by CoCreateInstance, which instantiates a COM object by calling IClassFactory::CreateInstance, which, in turn, calls the static CreateInstancemember function in your derived class.
The base classes use CFactoryTemplateto provide CClassFactorywith a template containing the CLSID of your object and a pointer to the static CreateInstancefunction for your object class.
Last updated on Tuesday, May 18, 2004