Called by the framework to retrieve data in the specified format.
The specified format is one previously placed in the COleDataSource object using the DelayRenderData or DelayRenderFileData member function for delayed rendering. The default implementation of this function calls OnRenderFileData or OnRenderGlobalData, respectively, if the supplied storage medium is either a file or memory. If neither of these formats is supplied, the default implementation returns 0 and does nothing.
If lpStgMedium->tymed is TYMED_NULL, the STGMEDIUM should allocated and filled as specified by lpFormatEtc->tymed. If not TYMED_NULL, the STGMEDIUM should be filled in place with the data.
This is an advanced overridable. Override this function to provide your data in the requested format and medium. Depending on your data, you may want to override one of the other versions of this function instead. If your data is small and fixed in size, override OnRenderGlobalData. If your data is in a file, or is of variable size, override OnRenderFileData.