See https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/8

This protocol should help us with buffer modifier decisions, especially regarding direct scanout, overlay planes and also multi-gpu cases.

See https://gitlab.freedesktop.org/wayland/weston/-/blob/main/clients/simple-dmabuf-feedback.c for a code example.

We just merged feedback support for Mutter 42, see https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1959. There's still some follow up work necessary to make it work for subsurfaces, but I have a local patch already applied and working.

With this in place, it's becoming interesting for Firefox: if we manage to implement it right, it should allow us to scan out WR tiles directly. For (hardware decoded) video this means we'll only do one copy (while also running the YUV -> RGB shader), which is already pretty good. The final step then is bug 1711461, which in some cases should allow us to scanout YUV buffers directly. But that is very hardware and decoder specific, in many cases we'll still need to do format conversion, i.e. do one copy (either in Firefox or the Wayland compositor).