Windows Version - Blank remote user's screen

Joe Ammann joe "at"
Thu, 16 Nov 2000 18:38:10 +0000

[ 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 greyed
 > out.  It is very hardware dependent (and therefore probably difficult to
 > 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

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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