When a screencast is started we do a roundtrip on get the offered
formats from wlr_screencopy. This roundtrip can fail [1]. In this case
the formats won't be initialized and we will just error out of the
screencast session.
[1] https://github.com/emersion/xdg-desktop-portal-wlr/issues/214
We teardown all existing screencast_instances using the removed output
by destroying the frame, removing all timers and then marking the
instance as ready for teardown so we can destroy it after the last connected
session is closed.
Any wlr_screencopy_frame_v1 has to be destroyed before the connected
output can be removed. Otherwise wlr_screencopy_frame_v1_destroy
segfaults the whole program. To ensure this we will make all frame
callbacks safe to be triggered for a previous destroyed frame.
wl_array is a better fit than wl_list. It's less intensive on memory and
fits nicely with the flow of dmabuf_feedback announcing all format
modifier pairs at once and reseting them on change.
The compositor can announce it's default rendering device via
linux_dmabuf_feedback as the main_device [1]. We should use this device
whenever possible. If aquiring this device fails we are adviced to use
force linear layout on buffers allocated with the implicit api.
With linux_dmabuf_v1 the modifier event is deprecated. Instead the
format_table event in combination with the tranches of
linux_dmabuf_feedback_v1 has to be used.
[1] https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/main/unstable/linux-dmabuf/feedback.rst
