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Re: [xougen] Re: [Xouvert-general] Network transparentcy and modules

From: Tyler Hall
Subject: Re: [xougen] Re: [Xouvert-general] Network transparentcy and modules
Date: Wed, 27 Aug 2003 21:33:29 -0500
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.3) Gecko/20030313

>> G-LiTe / wrote:

Tyler Hall wrote:


Now, for whatever reason I have to run down to the lab for an hour. While I'm there I realize I need access to the application already running on machine A. I go to machine B, log in as (or switch to) user1. I fire up my KDE/GNOME utility "grab window", and it can ask me for the target machine name (the one currently holding the window), or maybe it will do an X broadcast to search for valid X servers that will let me grab windows. To determine what to grab the utility connects to machine-A, authenticates me as user1, then queries the machine for all the windows it's currently hosting under sessions owned by user1, and asks the server to query each of those windows asking if it is capable of warping (ie. support the X11 warp extension). I am then presented with a list of warp-capable candidates, of which I can select one or all.


All this work can be transparent to the application. X clients using Xlib don't know what machine they're displaying on do they? Why should they be informed that they were just warped somewhere?


That is sortof what I was having in mind. It still doesn't really answer my questions though: - Where are we getting the addresses from? The gnome utility would have to know what X servers are running unless you want users to type in the address. - Would we allow the application itself to control (part) of this? Some Xlib functions for it?. The way I explained it above it's handled fully in Xlib. - How are we going to redraw the contents on the other X server? Is it possible to just send an expose event for the entire window? Or would we have to resend the current state of the window? There's two ways to do the latter, entirely on Xlib's side or the X server extension contacts the other server (in which case the other server needs an extension for it too) and sends a bitmap over.

Perhaps I shouldn't have buried my answers so deep, have a look at the paragraphs I've left from my original post. Let me clarify: Like someone else mentioned in their response, there will be few cases where you won't know the machine you want to grab windows from. But even if you didn't know it, or were too lazy to type it in, there are several solutions I can think of off the top of my head: Bookmarks, master lists (databases), or even broadcast. One of the enhancements to the Xserver could offer a "browse service", much like the samba server provides. Clients (apps) would send an X11 broadcast to the network asking for X servers. There's already a similar service for X logins, I haven't played with it much, but XDCMP (was that the acronym?) searches for valid XDM's on the network and lets you select one from the list to log into.

For the 2nd question, I don't think an application should even care about being moved to another server, for the same reason it doesn't know if it was executed to display on the local machine or a remote machine.

The 3rd response is somewhat the same, if you move a window completely off the screen (drag the title to the bottom) and bring it back up, the application has no idea what just happened, only that it was asked to redraw it's entire contents via a callback from the Xlib. Warping a window to another server should work exactly the same. The Xlib within the client opens the TCP/IP connection to the 2nd server, which DOESN'T KNOW the window is warping over because it thinks the application is just starting up and wants to display to its screen. At this point the *Xlib* in the client closes the 1st TCP/IP session (so the 1st server says good-bye and erases its window) and notes to itself to direct further draw responses to the 2nd connection. Well it just so happens that the 2nd server says "welcome to my screen, please do a full re-draw" which it considers the "initial draw". All this time the application itself has been dormant because it hasn't received any callback requests (draw requests). Finally when this 2nd Xserver says "full draw" the Xlib calls the application's callback and the application does it's normal thing.


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