Present extension based scheduler doesn't work well on NVIDIA drivers.
GLX_SGI_video_sync is less accurate, but is rumoured to work. See
[kwin's usage](https://invent.kde.org/plasma/kwin/-/blob/master/src/
backends/x11/standalone/x11_standalone_sgivideosyncvsyncmonitor.cpp)
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
I noticed sometimes full frame rate video is rendered at half frame rate
sometimes. That is because the damage notify is sent very close to
vblank, and since we request vblank events when we get the damage, we
miss the vblank event immediately after, despite the damage happening
before the vblank.
request next ...... next next
damage vblank vblank vblank
| | | ...... |
v v v v
---------------------->>>>>>---------
`request vblank` is triggered by `damage`, but because it's too close to
`next vblank`, that vblank is missed despite we requested before it
happening, and we only get `next next vblank`. The result is we will
drop every other frame.
The solution in this commit is that we will keep requesting vblank
events, right after we received a vblank event, even when nobody is
asking for them. We would do that for a set number of vblanks before
stopping (currently 4).
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
Factored out vblank event generation, add abstraction over how vblank
events are generated. The goal is so we can request vblank events in
different ways based on the driver we are running on.
Tried to simplify the frame scheduling logic, we will see if I succeeded
or not.
Also, the logic to exclude vblank events for vblank interval estimation
when the screen off is dropped. It's too hard to get right, we need to
find something robust.
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
Yuxuan Shui