VNC speed and compression

James [Wez] Weatherall jnw "at"
Thu, 23 Jul 1998 15:58:01 +0000

On Thu, 23 Jul 1998, Simon Byles wrote:

> James [Wez] Weatherall [mailto:jnw "at"] wrote on Thursday, July
> 23, 1998 2:50 PM:
> > I would tend to agree with this.  If WinVNC is sluggish on a 
> > P200 machine
> > then this suggests that either WinVNC has been misconfigured or that
> > something else in the system is taking up most of the 
> > available CPU time
> > and leaving too little for WinVNC to use. One obvious possibility is
> > that the Poll Full Screen option has been enabled by mistake 
> > for WinVNC,
> > which will cause a serious performance hit.
> This reminds me, I was a bit confused over the meaning and difference
> between these polling options. Is the general idea to have none on if
> you can and switch on an option or two if you need them? 

Yes.  The Polling options are there for use when a problem application is

> I'm running VNC server on an NT Server box (P200Pro) and Viewer on a
> P133 Win95 box across standard Ethernet (no switching). I did have Poll
> Window Under Cursor on and I put the sluggishness down to the busy
> network. But seeing this thread prompted me to look at the Task Manager
> and there I saw VNC's processor usage at 17-21% idle and 65% when I
> moved the mouse, 80%+ when I dragged a window about. So I switched off
> the polling and it now idles at 1%, going to only 21% dragging. The
> display updates slower (it "pauses") but I can live with that.

Really?  There is a special optimisation in WinVNC to allow windows to be
dragged properly.  This is coded in such a way that moving windows take
precendence over other updates, to give better feeback.  The result is
that when dragging windows around the screen in 'solid' mode, shadows of
the window get left on the screen and are only cleared up after you stop

> But do I need any of the polling on? Perhaps Poll Console Windows? Is
> there a known best compromise in this situation or do I just suck it and
> see?

The defaults are usually about right - Poll Foreground Window and Poll
Console Windows Only.  You might prefer Poll Window Under Cursor and Poll
Console Windows Only, though.


James "Wez" Weatherall
Olivetti & Oracle Research Laboratory, Cambridge, UK.
Tel : Work - 343000

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