One of the Mir issues we had been covering the most -- and one of our biggest gripes with it -- was over performance regressions when adding Mir/XMir to the rendering stack. Fortunately with composite bypass, most of those problems are gone for affecting OpenGL-based games on Ubuntu Linux. There's also numerous other shortcomings with this Canonical display server too.
Besides the multi-monitor support for XMir not being fully primed, Matthew Garrett has conveniently listed several other shortcomings of XMir at this time. Details in full can be found on Matthew's blog but from his eyes other problems include:
- Some systems have display corruption issues due to XMir poking the X.Org (DDX) drivers in different ways than normal.
- The input driver handling still isn't fully secure for the previously-reported XMir input security issue that Canonical tried to resolve.
- XMir doesn't support color profiles.
- RandR properties aren't exposed so users can't control TV output encoding, overscan, and other display attributres.
- There's still no hardware cursor support.
- Other features are still missing.
Matthew Garrett ended his note with, "It's clear that XMir has turned into a larger project than Canonical had originally anticipated, but that's hardly surprising. There's only one developer with previous X experience working on it full-time, and the announced schedule provided no opportunity to deal with unexpected problems. As if that weren't enough, there's obvious conflict between Ubuntu Desktop and Ubuntu Phone when it comes to developer time and required functionality. The one hardware vendor who's willing to take a public stand has demonstrated that they have no interest in supporting XMir, despite Canonical assuring people that they were already engaging in productive negotiations with GPU manufacturers." Matthew additionally suggests as an option Canonical just drop XMir entirely and focus their resources on the Mir-based Unity 8 desktop.