New GNOME Mutter Code Prepares Fractional Scaling For XWayland

A merge request was opened this week for plumbing fractional scaling support for XWayland clients running on the GNOME Mutter compositor.

Jonas Dreßler opened a merge request with a patch from Jonas Ådahl that has been working on the functionality for allowing scaling-aware XWayland clients to scale themselves using the scale-monitor-framebuffers functionality. The patch explains:

"When monitor framebuffers are scaled, this special cases Xwayland and sends output regions in a way that Xwayland think everything is N times as large as the logical region, where N is the ceil of the max monitor scale.

This is done by introducing a "stage" vs "protocol" coordinate space for X11, where the "protocol" coordinate space is "stage" multiplied by a scaling factor."

Dreßler noted in the merge request that the coordinate space conversion has been working out well. There is also a GNOME Settings Daemon MR for getting the UI scaling factor from a dedicated D-Bus API for X11 properties API exposed by Mutter rather than the display configuration API. The Mutter side of that work is still pending.

Being past the feature freeze for GNOME 46, short of it being unexpectedly allowed as a late addition, it won't be wrapped up until GNOME 47 in September. Similarly, also missing the feature freeze is the GNOME Variable Refresh Rate (VRR) functionality.

More details on other interesting GNOME development work this week can be found via the This Week in GNOME.