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From: Rob Roy on 7 Dec 2006 17:33
Hello,

My Win2K/XP UNIDRV-based printer driver has a feature to allow "pausing"
(via a MessageBox) the spooler at the beginning of each PAGE of a document.
This is needed to allow a user to tear off EACH page when using roll paper. I
was able to get this to work for 2K/XP by using the OEMDLL for OEMUNI sample
code from the DDK and adding a MessageBox call in the OEMStartPage() function
of "ddihook.cpp".

On Vista, however, the MessageBox does not work properly. The "Interactive
Services" comes up, and you can get to the MessageBox this way. But,
obviously, this is undesirable behavior.

Viewing the AsyncUI.doc file available on the following MS website,
http://www.microsoft.com/whdc/device/print/asyncui.mspx

it seems that the solution is to use SplPromptUIInUsersSession() function to
display the MessageBox instead.

However, I am having problems with this.
NOTE: I am currently using the Server 2003 DDK and the XP build environment
to create the OEMDLL.

Problems:
1. SplPromptUIInUsersSession requires "hPrinter" and "jobId" as parameters.
These are seemingly not available from the params passed into OEMStartPage.

a. I was able to get access to jobId by writing the same param sent to
OEMStartDoc to a global variable.

b. So, the problem now is seemingly with hPrinter. Though it appears to be
available as "pdevobj->hPrinter", this does not seem to work.
SplPromptUIInUsersSession is returning FALSE, and GetLastError() is returning
6, i.e. ERROR_INVALID_HANDLE.

c. If I try using "pdevobj->hEngine" instead, this doesn't fail, but it
never posts the MessageBox. And, it doesn't seem to actually return. But, it
also doesn't keep the print data from getting to the printer either. So, I
don't really have any idea what happens in this case.

Questions:
1) Is it possible to get access to the hPrinter that
SplPromptUIInUsersSession needs? If so, how?
2) Is there a better approach available to posting a MessageBox to the user
at the beginning of every page? If so, what is it?

NOTE: The GPD file seems to provide a mechanism for this via the
*rcPromptMsgID Option Attribute. But, my experience with this years ago was
that it didn't work. And, even if it does work, the only options it seems to
provide is to post a message at the time the user chooses the feature on the
UI (using UISETUP for *PromptTime) or at StartDoc time (using PRTSTARTDOC).
There is no way to set this to be displayed at every page of a document as we
require.

So, I am open to suggestions.

Best regards,
Rob
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