This commit assumes that cursor surfaces work in a "mailbox" fashion. If
they are painted multiple times before a successful flip, all commits
but the last get discarded, and the last commit gets presented after the
flip succeeds. This is more or less how it works in the atomic backend,
and also more or less how it works in other backends, with the exception
that the cursor painting might fail without any way of knowing. This
assumption is still better than unconditionally discarding all cursor
surface feedbacks as if the cursor painting always fails.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1484>
Regarding the sequence = 0 fallback: in some cases (moving a cursor
plane on atomic amdgpu) we get sequence = 0 in the page flip callback.
This seems like an amdgpu bug, so work around it by assuming a sequence
delta of 1 (it is equal to 1 because of the sequence != 0 check above).
Sequence can also legitimately be 0 if we're lucky during the 32-bit
overflow, in which case assuming a delta of 1 will give more or less
reasonable values on this and next presentation, after which it'll be
back to normal.
Sequence is also 0 on mode set fallback and when running nested, in
which case assuming a delta of 1 every frame is the best we can do.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1484>
The presentation-time protocol allows surfaces to get accurate
timestamps of when their contents were shown on screen.
This commit implements a stub version of the protocol which correctly
discards all presentation feedback objects (as if the surface contents
are never shown on screen). Subsequent commits will implement sending
the presented events to surfaces shown on screen.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1484>
