SDL Now Supports Wayland's XDG-Shell

The SDL library that's most commonly associated with being an abstraction layer used by Linux games now has Wayland XDG-Shell support.

SDL2 has continued offering good Wayland support and the latest work on this back-end by Ryan Gordon is adding XDG-Shell support. XDG-Shell is used for managing surfaces under Wayland compositors in dealing with window dragging/resizing/stacking and other actions.

Gordon commented in the commit today:

This is meant to be the desktop-enhanced version of wl_shell. Right now we just match what the existing wl_shell code does, but there are other areas of functionality available to us now, that we can fill in later.

This uses the "unstable" API, since this is what ships in Ubuntu 17.10 (as part of Wayland 1.10), but Wayland 1.12 promotes this to stable with extremely minor changes. We will add support for the stable version when it makes sense to do so.

This improvement will be found in the eventual SDL 2.0.8 release. Other work so far for SDL 2.0.8 includes a Metal 2D render implementation on macOS, experimental WASAPI support on Windows UWP, and some API additions.