[META] Wayland

Tasks

Here are some things I've been thinking about regarding wayland, I may add more if they occur to me.

• Don't destroy wl_display and wl_surface until quit
  Currently gfx drivers are destroyed on core launch and fullscreen transitions.
  This would allow the splash screen to be displayed on launch rather than on fullscreen and core transitions.
  Currently the android keeps it's surface as a single surface is provided on application launch. It does this will a global if I recall correctly. Maybe window management should be split out of the gfx driver.

• Remove the splashscreen.

• xdg_toplevel configure events should stored until the xdg_surface configure at which point they're applied and acked
  I think is handled correctly by libdecor but without libdecor currently RetroArch just acks the configure.
  https://github.com/libretro/RetroArch/blob/3e6486db2be523829bc22841c4a30b674978e9bf/input/common/wayland_common.c#L664-L669

• Bumb protocol versions
  This can require implementing new event handlers, some of which are okay to ignore. However it can also require larger changes.

• Use wl_event_queue to decouple display and input threads
  When threaded video is enabled the wayland fd is read from the video and input threads.

  • Take more care with queue and dispatch, use libdecor_dispatch where appropriate.

• Drag and drop https://github.com/libretro/RetroArch/pull/16443
  My attempt at implementing this crashes RetroArch and depends on glib for URI decoding.

• wp_presentation

• wp_color_manager

• Rewrite wl_output structs

• xdg_toplevel_icon

• Stop dynamically loading libdecor?

• Version gate libdecor features

• Use XDG_TOPLEVEL_STATE_RESIZING to rate limit framebuffer allocation

Links

Wayland Vulkan WSI docs
mesa Wayland Vulkan WSI implementation
Wayland protocols

Testing strategy

Run nested kwin (env WAYLAND_DISPLAY=wayland-1):

kwin_wayland --xwayland --no-lockscreen  --width 1920 --height 1080 --output-count 2

--output-count 2 will cause retroarch to show a splash screen. --output-count 1 will forego the splash screen.

Run nested mutter (env WAYLAND_DISPLAY=wayland-1):

MUTTER_DEBUG_DUMMY_MODE_SPECS=1920x1080 dbus-run-session -- mutter --nested --wayland

Run with limited CPU, useful for debugging race conditions:

systemd-run --user --pty --same-dir -p CPUQuota=1% --setenv=WAYLAND_DISPLAY=wayland-1 ./retroarch

Build without libdecor for testing raw xdg-toplevel implementation:

./configure --enable-debug --disable-libdecor

This is a broad Wayland task list rather than a single scoped change. Start with input/common/wayland_common.c for the configure-event item, or choose another unchecked task and trace its relevant entry point. Use the nested kwin or mutter commands in the issue, and consider the selected task done when its behavior is implemented and tested in the described environment.