Connecting Xmir to USC fails [std::exception::what: An output ID must be specified from src/server/shell/system_compositor_window_manager.cpp(66)]

[Josh Arenson]

As seen here https://unity.ubuntu.com/mir/using_mir_on_pc.html

I should be able to install ubuntu-desktop-mir and run unity7, but instead I receive the following error:

failed to create a surface: Error processing request: An output ID must be specified
Internal error details: /build/mir-1tnxlh/mir-0.18.1+16.04.20160115/src/server/shell/system_compositor_window_manager.cpp(66): Throw in function virtual mir::frontend::SurfaceId mir::shell::SystemCompositorWindowManager::add_surface(const std::shared_ptr<mir::scene::Session>&, const mir::scene::SurfaceCreationParameters&, const std::function<mir::IntWrapper<mir::frontend::detail::SessionsSurfaceIdTag>(const std::shared_ptr<mir::scene::Session>&, const mir::scene::SurfaceCreationParameters&)>&)
Dynamic exception type: boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<std::runtime_error> >
std::exception::what: An output ID must be specified

[Daniel van Vugt (vanvugt)]

A weird proposal. I guess this will crash. But it's really an enhancement request to ask for XMir (with Unity7 or anything inside it) to run under Unity System Compositor.

[Daniel van Vugt (vanvugt)]

OK, here's a quick workaround for Xmir to get things going:
https://git.launchpad.net/~xmir-team/xorg-server/+git/xmir/commit/?id=18ee4ec59c1ab47c857205d6abbcdc5881ec2f9b

It's a workaround and not a fix because a proper fix will have to occur in Mir itself. Mir's "system compositor" mode needs to be enhanced to not reject surfaces that don't select and fit a physical display. So this will only work with a single monitor. And it will only work after we figure out this USC issue: bug 1548210

Once Mir gets fixed, the workaround in Xmir should be reverted. And theoretically we could then have multi-monitor Xmir inside Mir.

[Daniel van Vugt (vanvugt)]

Reverted. I changed my mind; that approach might break Unity8 and others that want a root window in a window.

We need a proper solution. Either:
  (a) Mir understand and accept client windows can be bigger than one output; or
  (b) Xmir chop up the root window and display it as separate surfaces (difficult, lots of work).

[Reinhard (rkalx93)]

I'm getting this issue on the stable 16.04 Ubuntu. Does this mean Mir should not (cannot) be used in this combination on Xenial ? I merely like to have a test system with similar behaviour as the mobile one as development on PC is much easier than on tablet/phone alone.

[Daniel van Vugt (vanvugt)]

The same behaviour as on mobile is:
   Xmir -> Unity8 -> USC
which works.

This bug however is about:
   Xmir -> USC
without any Unity8.

[Michał Sawicz (saviq)]

Syncing task from Mir.