How To Pass Context Data With TWAIN Callback Routine

[xiaoyuan]

I register a callback routine to the TWAIN event as follows:
TW_CALLBACK callback = {0};
callback.CallBackProc = (TW_MEMREF)TwainCallback;
TW_UINT16 ret = DSM_Entry( DG_CONTROL,
DAT_CALLBACK,
MSG_REGISTER_CALLBACK,
(TW_MEMREF)&callback );

Inside the TwainCallback routine, I need to access some user context data. How do I pass such user data (an object) here with calling register so that it can be retrieved inside the callback function?

Thanks.

[Author]

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