[Pkg-xfce-devel] Bug#564694: Bug#564694: xfdesktop4: Crash when moving desktop icons on secondary screen

[S. Raase]

Hello,

>>>> For your information, I do not use the TwinView feature for DualHead of
>>>> the nvidia driver (which essentially implements some Xinerama), but
>>>> instead the basic way of X11 using one server and one x-screen per real
>>>> screen. These screens are completely separate.
>>> Then I fail to see how it can't be reproducible with another driver.
>> Tell me of a driver which can product two X screens on one server and
>> I'll try. I've just never seen some other driver for hardware I posess.
> 
> Well, if it's not a specific feature of nvidia driver, all. If it's a
> specific feature of the nvidia driver and we have no way to debug it,
> end of the story.
> 
An X-Server may control an arbitrary number of screens, which appear to 
the system as completely different. Like every hardware output may 
appear as a screen (like in my case). There are referred to as ":0.0", 
":0.1", ":0.2", and so on. This is a standard feature of X11 since dawn 
of time.

Or I may start a new X-Server for every output, each containing just a 
single screen. These are then called ":0.0", ":1.0", ":2.0" and so on. 
In recent times, both concepts for multiheading are dying, because X11 
does not allow moving windows from one screen or server to another.

I do not know of many X11-drivers which make use of screens, they might 
have existed in XF86_3-times. Multimonitoring was not important back 
then. If a driver does not make use of this concept at all, it is still 
a standard X11 feature...

> So could you explain what exactly is the “two X screens on one server”,
> how do you configure it (I guess your previously attached Xorg.conf
> might help) and what exactly do you run and how. Something like a bug
> report. Something with which I can work to try to reproduce the problem.

Multimonitoring on NVidia graphics cards is possible in three ways:
(a) binary nvidia driver using nvidia TwinView (ati has something 
similar but called differently), which in essence is a Xinerama 
extension, and as Xinerama is deprecated in favour of XRandR 1.2+ and 
applications have to be Xinerama-aware, I don't like it. (3D 
acceleration does work with binary nvidia drivers.)

(b) binary nvidia driver using the standard X Screen approach, which 
means that one server controls the graphics hardware and provides two 
separate X Screens (:0.0 and :0.1). This is the way I use it, as 3D 
works on both monitors and as they are completely separated applications 
have no idea where they are displayed. XFCE4 does know about this 
approach, otherwise I would have to run a window manager on every screen.

(c) the modern approach with XRandR 1.2+ which is using a huge virtual 
framebuffer and providing different "views" onto it, while at the same 
time providing video signals in a specific resolution and without 
panning. This is the preferred way in the future, but NVidia will not 
implement it in their drivers.

Take a look at my Xorg.conf and you see how I set up the separate 
X-Screen approach; I tell the server I want multimonitoring but no 
Xinerama and then the binary driver sets it up accordingly.

> I was more interested about X stuff.

Nothing. But the bug might have slipped my attention completely, as I 
seldomly shuffle my icons around to the places where they already are.

> Well it doesn't look really usable. Try to kill xfdesktop first, then
> run it directly from gdb so you are able to break on gdk_x_error.

If I kill xfdesktop it is started again automatically. Anyway, there are 
a lot more small caveats with XFCE4 on a separate X-Screen. (Like after 
clicking into the task list the pointer has to leave the task bar before 
any other clicks will be accepted; they are silently ignored instead.)

> But, as said before, I'm not really interested with debugging on a
> binary driver.

Then I would propose that you close the bug and mark it with "I'm not 
interested and I won't fix it."

I can live with this bug although it is a somewhat nasty one. As is the 
case with most bugs - if they are known they are not dangerous.
Anyway, if the multihead support (or separate x-screen support) in XFCE4 
is largely untested and people are unwilling to take care of it, then 
they should drop it completely. This way one can run whatever 
environment on any screen, which is one advantage of this approach; 
think about XFCE4 on your monitor and wm2/icewm/whatever on a TV screen.

Best Regards