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A thousand things I never wanted to know about X

In the last few days, I have replaced the two 20 inch CRT monitors that I have hardly used the last years with two 20 inch TFT displays, and my company (finally) gave me a 19 inch TFT display to accompany my notebook display at work. Maybe I should take that as a hint that they want to see me in the office more frequently rather than in my home office which I generously use these days. At home, I built a "new" computer from mainly used parts to drive the two 20 inchers.

I have learned a lot about X in the last days, but spent too much time with it.

I have been running my Desktop with older X and two CRTs for quite some time, but I hardly ever used it due to the setup of my now ex-flat. Back then, I learned that the "two monitors, one display, one screen, one desktop" option of X was called Xinerama and statically configured: You write down your display layout in xorg.conf and it uses it. Configuration changes mean restarting the X server.

KDE notices Xinerama automatically, designates one monitor the "main monitor" and displays its panel there. You can move windows from one monitor to the other one, but changing virtual desktops always changes what both monitors display. This is not really what I want, since I often have "static" contents (news reader, mail reader, chat windows, help screens etc) on one monitor while I do my normal work on the other monitor, which involves changing virtual desktops.

So I was rather happy when I learned upon the arrival of the external TFT display for the notebook that you can work without Xinerama. In that case, the X server comes up with one display and two screens, which KDE uses to display two independent desktops which can be independently configured, but can both be accessed with one mouse and one keyboard.

For me, this means that I finally can independently change virtual desktops on both monitors, but pay the price that I cannot display a certain virtual desktop on monitor 1 now, and on monitor 2 in five minutes, and that a window opened on monitor 1 is never going to be shown on monitor 2 without serious interference. This looked ok for me. Additionally, you can use different font sizes on the different monitors as defaults, which comes in handy if both monitors are blatantly different in size (which is the case with the notebook and its external monitor).

However, with that setup, KDE seems to be challenged when it comes to saving the configuration. Some things (such as desktop background and panel config) seem to save fine, desktop independent, other things (such as open windows and their position) are lost when the session exitst. My daily visit to Kevin&Kell (which used to be in a browser window that was saved with my session) has badly suffered since then.

Then, a few weeks ago, somebody talked me into trying the X server from experimental. Which is when my dual-desktop setup ceased working.

The nice people on #debian-x told me that Xinerama is a thing of the past, and is currently in the process of being replaced by Xrandr 1.2. The removal of "my" two monitor, two screens, two desktop setup is collateral damage, and if I still want that behavior, the upstream considers this an issue to be handled by the Window Manager / Desktop Environment now. Gee, thanks. That's what I call a regression.

After spending half a day cursing and ranting, and even considering to go back to lenny's (or even etch's), I finally settled on going with the "new" way as I was going to lose my independent desktops sooner or later anyway. Again, with the friendly help of the people on #debian-x, I found out about a lot of advantages of the latest X servers.

In most basic cases, the latest X server does not need a configuration file any more. It autodetects your hardware and chooses whatever modes it finds optimal. It does a pretty decent job in doing so. If one wants to influence how the X system comes up, once can always write an Xorg.conf file - the configfileless server even writes the "virtual config file" it uses to the log as a starting point.

Additionally, almost everything regarding screen layout can be reconfigured at run time using the xrandr binary from a command line. Even a hardware change (such a new monitor plugged into the powered on notebook) is correctly detected. Cute. This allows me to reconfigure my notebook depending on where it currently is and which external monitor (or projector) is connected.

This can be perfected if I find out whether X offers a hook to plug a reconfiguration script into that is called when the X server starts or when the system is waking up from standby or hibernation with the X server running. A lot to do, and great potential for elegant stuff.

However, while I am talking about hibernation, this is a downside of the new driver: When the system wakes up from hibernation, the X server sometimes confuses itself enough to become nearly unuseable: I had it become psychotic when plugging in the external monitor (which can do 1600x1200 points) after waking it up from hibernation at the office. The internal display can only do 1400x1050, and the box thought that the external monitor only had 1050 y axis pixels, displaying bit garbage in the lower part of the big monitor, and showing a useable, but unintelligible panel. When opening any browser or any other application with considerable text amounts in the window, all fonts become unreadable once one scrolls down. Restarting the X server helps and everyting is fine. But I do not use hibernation to force myself to log out of X after waking up. After going back to the "one monitor mode", the X server now thinks that my virtual desktop is 1600x1200 and only shows 1400x1050, with dead space at the right and lower side of the virtual desktop. xrandr does not allow me to reisize the FB below 1600x1200. No idea what's going on here.

In most of the cases, calling xrandr --auto for each output will fix the issues at run time, but sometimes a session restart is needed. Code needs to stabilize quite a bit before becoming useable in production.

There are a few disadvantages that will remain: Both monitors will change their contents when the virtual desktop is changed, and both displays will use the same default font size (which might be inappropriate if both displays are of different size). But I think, when the issues are cleared up, that I can live with these disadvantages.

The "new" desktop system that I built has a Matrox G450 dual head graphics card, and unfortunately, the Xrandr 1.2 enabled X server from experiemental has shown to be unuseable: Upon some mode changes, the X server goes into an endless loop and proves itself to be unkillable short of SIGKILL. And if it dies, it sometimes pulls the entire system with it. There is a corresponding bug in the upstream BTS, but it hasn't received any noticeable attention by the upstream developers.

So I might find myself configuring one last Xinerama config before I can finally completly migrate to Xrandr 1.2 on the desktop as well.

Then I'll probably need to bug the KDE upstream people to implement a two-desktops-on-a-single-screen feature in one of their future versions so that I can get my independent-desktop-things back. But that's a far far away future.


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Simon on :

You might be able to get devilspie to automatically make everything on the second screen automatically appear on every virtual desktop - I don't know whether it has the appropriate matchers, but I'm sure Ross Burton would include them in the next version if he knew they were wanted.

Marc 'Zugschlus' Haber on :

How well does devilspie (a program that probably is GNOME-related) integrate with KDE?

Jason D. Clinton on :

Drivers? I suspect that most of your lockup issues are related to the Matrox drivers. I'm using the new "modeless Intel" graphics driver in the manner you describe on both a desktop and a laptop and everything is stable.

Björn Schließmann on :

Hello Marc,

at EBD, we are using quad-head Matrox G450 with Xorg from Etch and Xinerama (for ESTW computers, amongst others). A problem I couldn't fix yet is comparably low performance because using Xinerama excludes HW acceleration. :-( I'm not sure to what extent you have this problem with two screens, but could you please let me know if you manage to enable HW acceleration in some way with your configuration?



P.S.: Bist du am 10.11. zufällig in Gotha? :-)

Will Thompson on :

xmonad's workspace model matches what you want pretty well. But if you don't want a minimalistic window manager configured in Haskell, xmonad may not be for you. :-)

Danny on :

There's always Xnest :-)

Marc 'Zugschlus' Haber on :

Yeah, sure, the ati driver is just fine as well. It's the matrox stuff that is not quite stable at the moment.

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