The GSoC wrap-up

And so, another Summer of Code has ended. During the past three months, I was working on Mutter, a GNOME's Compositor. My main goal was to make Mutter, which was written as an X11 Window Manager more than a decade ago and recently ported to also be a Wayland compositor, start Wayland session without requiring X server (Xwayland) to be present. That goal was accomplished, and Mutter is now able to start without Xwayland being started. Other goals included making Wayland clients start without X11 being present, which wasn't accomplished (or even started), because after main goal was finished, there was only a week left before this evaluation, and nothing could be accomplished in that time, given the complexity of the task.

So, lets sum what needed to be done during these past three months:

- First task that I worked on was splitting X11 specific part from main display object, MetaDisplay. That code was moved into a new object, MetaX11Display, which is owned by MetaDisplay and is either created or not created at startup, depending on how Mutter was started. A more detailed explanation can be found at [1].

- Second task involved getting rid of MetaScreen object, an object which previously had more than one instance, that nowadays has only one. MetaScreen contained both X11 and non-X11 specific parts, so it was split between MetaDisplay and MetaX11Display, accordingly. A more detailed explanation can be found at [1] and [2].

- Third set of tasks (yes, set of tasks) involved getting X11 specific functionality out of objects managed by MetaDisplay. These include workspace management, startup notification, stack tracker and bell (visual/sound notification). A more detailed explanation can be found at [3] and [4].

- Final task involved getting rid of GDK usage early in the code, and moving control of GDK X11 display to MetaX11Display itself. This also involved (sadly) getting rid of some GtkSettings usage which was used to change some properties when it gets changed in GTK. A more detailed explanation can be found at [4].

- After the final task was done, a --no-x11 switch was added to Mutter command line, which can be used to start Mutter without starting Xwayland.

- Bonus tasks, which did not really need to be done in order for Mutter to be able to work without X11 included renaming and improving X11 error management code (x11 trap code), moving workspace management code from MetaDisplay (previously MetaScreen) into new object - MetaWorkspaceManagement, and getting rid of screen size tracking in MetaDisplay (again, previously MetaScreen), and utilizing MetaMonitorManager directly. A more detailed explanation can be found at [3] and [4].

During this effort, a lot of functions were removed or replaced by functions with different names/parameters. Any compositor using libmutter library (gnome-shell is its most known user) cannot be compiled against my Mutter branch. However, I did create an API changelog which can be found at [5], for those that want to make use of my work, which can now be found at [6], and is rebased against current git master, as of moment of writing. Instructions to try out the compositor code can be found at [4], as well.

This summarizes my work done over these past three months. I'd like to thank both of my mentors, Jonas and Carlos, for helping me when I got stuck, providing feedback whenever it was necessary, or answering calmly and kindly at any of my questions, however simple or stupid they might sound. Also, I'd like to thank Google and GNOME Foundation for accepting me as student developer and allowing me to participate in this year's Summer of Code.


Update 2017-08-27:

Since the original blog post, Jonas has found some time to do a review of my work. I have implemented most of his feedback into a new branch [7]. The changes were mostly cosmetical, with no functional changes related to previous reports.



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