Windows Version - Blank remote user's screen

Eric Swarthout eswarthout "at"
Thu, 16 Nov 2000 18:56:03 +0000

I had posted to the list probably six months back about wanting to do this,
but instead of going to a blank screen have a full screen image appear that
said something like "System Service in process".  My company puts
Information Kiosk in public locations, so if we blank the screen it looks
broken, but there are sometime where i need to do so maintance.  Has anyone
given this any thought?  I know last time someone suggested doing something
in DirectDraw to write to the screen.

----- Original Message -----
From: Joe Ammann <joe "at">
To: <vnc-list "at">
Sent: Thursday, November 16, 2000 1:32 PM
Subject: Re: Windows Version - Blank remote user's screen

> [ On Wednesday, November 15, 2000 at 10:17:36 (-0600), Dan Fulbright
wrote: ]
> > Subject: Re: Windows Version - Blank remote user's screen
> >
>  > > This is something I thought about doing at one point, but never
>  > > actually got round to it.  The way I was considering was to make
>  > > use of the monitors power saving features to disable it, rather
>  > > than to actually "black-out" a screen.  Some problems with this
>  > > one might be:
>  >
>  > FWIW, PCAnywhere cannot always blank the server's screen.  After my
>  > department all got new monitors, the option to blank the screen was
>  > out.  It is very hardware dependent (and therefore probably difficult
>  > implement in WinVNC).
> I have done this "black-out" in WinVNC, and can confirm that it really
> is hardware dependent as hell! Being more of a Unix than a Windows
> hacker, I got in contact with a company specialised in doing graphics
> drivers in Windows.
> I ended up getting a DLL as an interface to a device driver, with
> basically 2 functions, let's call them TurnOffScreen() and
> TurnOnScreen(). It will activate the power saving feature of the
> graphics card by twiddling with the registers on the card, so you
> _really_ are hardware dependent!
> It works well for me, but as one of the previous replies suggested, it
> is quite hard to keep the screen black. Moving the mouse is not a big
> problem, because stock-WinVNC has the option of disabling the
> mouse. The problem is hitting Ctrl-Alt-Del! I could only work around
> that by having another background thread in WinVNC that monitors the
> registers in a rather tight loop and turns the screen off again when
> it becomes active. Takes about 0.1% of CPU time, so not a huge
> problem.
> Now the bad news: The graphics driver and DLL is not OpenSource. If
> you're still interested, drop me a note and I'll get you into contact
> with the vendor. You can then easily have my changes to WinVNC to make
> it work.
> HTH, Joe
> BTW: This works in many cases where PCAnywhere fails.
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