unity-2d on multi-monitor system has many problems

[Joshua R. Poulson]

1) the launcher did not appear on either monitor

2) top panel appeared on the left-most monitor instead of the primary display

3) launched applications did not have their menus appear properly at the top of the screen

[Florian Boucault (fboucault)]

Thanks for the bug report Josh.
Would it be possible for you to attach a screenshot? (especially for point 3)

[Ugo Riboni (uriboni)]

FYI, issue 2 seems to be a problem in Unity too. Quoting from code in unity/targets/mutter/plugin.vala :

      /* FIXME: This needs to always be monitor 0 right now as it doesn't
       * seem possible to have panels on a vertical edge of a monitor unless
       * it's the first or last monitor :(
       */
      screen.get_monitor_geometry (0, // Should be screen.get_primary_monitor()
                                   out primary_monitor);

[Florian Boucault (fboucault)]

An interesting read we may be inspired by:

https://bugs.launchpad.net/ayatana-design/+bug/683084

[Mark Shuttleworth (sabdfl)]

Yes, we should definitely only have one approach to the problem :-)

[Olivier Tilloy (osomon)]

I can reliably reproduce points 1 and 2 in the bug description.

Note that regarding the first issue, the launcher is running, but it’s not visible on any monitor. If one launches manually another instance of unity-qt-launcher, it appears at the left of the leftmost monitor instead of the primary display.

As to points 2 and 3, according to the specification (https://wiki.ubuntu.com/MenuBar#Presence), the panel (aka the "menu bar") should appear at the top of every screen, except those screens where a window is currently in full-screen mode.

[Florian Boucault (fboucault)]

Unity related metabug: https://bugs.launchpad.net/unity/+bug/661450 "Support for multiple monitors broken"

[Florian Boucault (fboucault)]

Fixes for panel and launcher placement are going to land soon in trunk. Mostly it's about having the same code path used in both cases and cleaning it up a little bit. It does not take into account the multi monitor case mostly because the struts are badly set.

"Struts MUST be specified in root window coordinates, that is, they are not relative to the edges of any view port or Xinerama monitor.
[...]
 Another example is a panel on a screen using the Xinerama extension. Assume that the set up uses two monitors, one running at 1280x1024 and the other to the right running at 1024x768, with the top edge of the two physical displays aligned. If the panel wants to fill the entire bottom edge of the smaller display with a panel 50 pixels tall, it should set a bottom strut of 306, with bottom_start_x of 1280, and bottom_end_x of 2303. Note that the strut is relative to the screen edge, and not the edge of the xinerama monitor.
"
from http://standards.freedesktop.org/wm-spec/1.3/ar01s05.html paragraph _NET_WM_STRUT_PARTIAL

[Florian Boucault (fboucault)]

https://bugs.launchpad.net/bugs/726680 is a new addition to the multi monitor problem.

[Olivier Tilloy (osomon)]

Also see bug #735937.

[Bill Filler (bfiller)]

based on discussion with Olivier today, the goal is the following:
1) get mirroring working first (i.e. all screens showing exact same thing launcher/panel, etc.). This is a must have.

2) analyze effort to get extended mode working (i.e. external monitor just displays blank desktop where you can drag windows to)

[Olivier Tilloy (osomon)]

I just tested a live CD of the latest version of Unity. When I plug in an external monitor, the default behaviour is *not* mirroring, it extends the desktop to the second monitor. The launcher is present only on the primary screen. Each screen displays an instance of the panel. The applications menus will be displayed in the panel of the screen that contains the largest part of the corresponding window. The dash always shows up on the primary screen, regardless of where the mouse cursor is when invoked.

Now testing Unity-2d, when I plug in an external monitor, the default behaviour is consistent with Unity: the desktop extends to the second monitor. However the second screen doesn’t have a second instance of the panel. This is the only discrepancy I can observe. The other components behave the same.

Now for the mirroring use case: it just works out of the box, as it’s handled lower down the stack.

To sum things up: at the moment the only discrepancy we have with Unity is the lack of a panel on each screen when in "extended desktop" mode.

[Florian Boucault (fboucault)]

The problems reported in the description of this bug are actually fixed.

The last issue we want to tackle (displaying one panel per monitor) is tracked by bug #683084