Thank you for your response Corne.
If you make screen captures of the entire screen at small intervalls ( say 50ms), you'll use a lot of processor time on a Win32 PC.
I don't know. The major cpu usage is in the compression.
VNC apparently doesn't need a lot of processor time. That's why I gather VNC only makes screen captures of the screen areas which have changed. Unfortunately it's not clear to me how it's done. Is the screen divided in a certain number of regions ( say 10),that screens captures of each region are made, and if something new happens in some of the regionx, the server only makes screen captures of the regions where something has changed?
I'm sorry but I'm not that deep into the vnc source, definitly not on M$Winodws. I only use it and twiggle a little with the polling settings.
Since I did that because I was on a low bandwith connection, I saw the slow update.
Some (10) years ago, I was a developper and I do know how to read source code but currently I don't take the time to do so, definitly not for something I don't need to twiggle with.
If so, how does VNC know that something has changed on the screen ? If you only wait until a keyboard or mouve events occurs you can miss changes on your screen.
On M$, vnc does not know if something has changed, the comparision takes way to much resources (memory and processor power) It expects things to be changed (or not). I don't know what meganism triggers that, I do know it has some flaws, specially if tools are not written using the standard M$Windows libraries.
Could you help me ?
no.
btw: in the archives (discussed a couple of months ago) there was a little tool called rfbcounter or rfbclock or such. It just generates pictures and you can view that with a vncviewer. It was all verry basic code but nice and small to start learning the vnc concept. See if you can find that.
CBee
Thank you in advance
Serge
-----Message d'origine----- De : Corni Beerse [mailto:[EMAIL PROTECTED] Envoyi : mardi 6 janvier 2004 17:30 @ : Castelier Serge (RBFM/ASQ1) *;
[EMAIL PROTECTED] Objet : Re: How does RealVNC know when to make a screen
capture
Castelier Serge (RBFM/ASQ1) * wrote:
Hello
I downloaded the source code of VNC and had a look at it.
Apparently VNC makes screen captures for a Win32 PC by using API's such as GetDIBits(). But it's not clear to me how the server part of the
application knows that something has changed on the screen of the PC.
Furthermore ,I don't
It does not know that. That's why you can configure several polling options
in the vncserver. It just peeks at some regular interval or when it expects differences (like mouse or keyboard actions).
know if VNC makes a screen capture of the entire screen or just of the part that has been changed.
That's also one of the polling options.
I saw in the source code that regions are beeing used with API's such as GetRegionData() and I gather VNC is using regions to determine which part
of the screen has to be refreshed, but I'm not familiar with regions and I
didn't manage to understand how it works.
In the end, I expect/experienced it does just some matrix over the polled area and sends the updated rectangles. I don't know for sure.
Can anyone help me ?
Thank you in advance
Serge Castelier _______________________________________________ VNC-List
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