O/S hooks question

[Ho-Kuo Chan]

Ahhh, yes thanks Jonathan. What you pointed out made me realize something about
VNC: although a client might request a frame buffer update, the server will not
necessarily send the update right away - it waits until there has actually been
a change to the rectangle in question, thereby saving CPU and bandwidth time.
Thanks again!

Ho-Kuo Chan
Matrox Networks

Jonathan Morton wrote:

> >Hello,
> >    I am new to this mailing list but have read the FAQ and searched the
> >archives but can't seem to find an answer to my question: why does the
> >VNC Server need hooks in the O/S (or X-Windows) to be notified of screen
> >changes? It would seem to me that the Server need only check the frame
> >buffer when the client requests a screen/framebuffer update. Am i
> >missing something? Thanks in advance for your help.
>
> Performance reasons, plain and simple.  It takes a helluva lot of CPU power
> to poll the screen for changes, and it's much easier just to get the
> graphics subsystem to notify VNC of what's happened on a need-to-know basis.
>
> In fact, the WinVNC server has problems with this, because Windoze doesn't
> tell it everything that goes on, so it still needs to poll the screen at
> regular intervals to make sure it catches everything.  It shows - WinVNC
> requires a decent Pentium to run well, whereas MacVNC works very quickly on
> a very modest PowerMac (I haven't experienced Xvnc for myself, but i guess
> it's just as quick as MacVNC).
>
> --------------------------------------------------------------
> from:     Jonathan "Chromatix" Morton
> mail:     chromi "at" cyberspace.org  (not for attachments)
> uni-mail: j.d.morton "at" lancaster.ac.uk
>
> The key to knowledge is not to rely on people to teach you it.
> --------------------------------------------------------------
> Contributing to the VNC Project - http://www.uk.research.att.com/vnc/
> Ask me for Macintosh VNCserver v3.3.2 beta2.1
> v3.3.2 beta 2.2 due out soon!
>
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