GNOME's Mutter Adds XWayland Full-Screen Games Workaround
The work by the prolific Red Hat desktop developer is for X11 games that rely upon XRandR to change the resolution while also using the NET_WM_STATE_FULLSCREEN window manager hint when going into full-screen mode.
The xrandr + NET_WM_STATE_FULLSCREEN combination used by some Linux games expects the full-screen window to have the size of the specified "fake" RandR resolution. This change is in-step with recent XWayland support in the X.Org Server code-base for supporting faked XRandR resolution changes and then scaling the contents to match the monitor's actual full-screen resolution.
Games making use of the SFML 2D game library and OGRE are among the titles needing this workaround support for full-screen gaming.
The Mutter change can be found here while the xorg-server/XWayland side change was merged in October and will be present in whenever the next X.Org Server release finally materializes.