The start phase creates the MetaDisplay object, and initializes Wayland, and
creates the main loop.
The run phase runs the main loop and handles returning an error if the
context was terminated with an error.
The terminate phase terminates the main loop, with or without an error.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1861>
Configuration is the first step of the lifetime of a context, after
creation; it's here where argc/argv is processed, and it's determined
what kind of compositor, etc, it is going to be.
The tests always run as Wayand compositors, so the configuration is
quite simple, but will involve more steps later on.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1861>
It'll be part of and owned by MetaContext, intending to replace
`meta_is_wayland_compositor()`, but place it in a new file for public
enums so that it can be used from wherever.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1861>
This introduces a MetaContext implementation aimed to be used for test
cases, with as little boiler plate as possible needed in the test.
It currently doesn't do anything, just fills out the GObject boiler
plate and sets a name.
Build it into every core test, for compilation, even though it isn't
used anywhere yet.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1861>
This type is intended to replace the scattered functions used to
configure how the Mutter compositor is run. It currently doesn't do
anything, and only has a human readable name, intended to be set to e.g.
"GNOME Shell".
It's an abstract type, and is intended to be used via either a future
`MetaContextMain` for real display server use cases, and a
`MetaContextTest` for test cases.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1861>
This job does:
1. Download the coverity bundle and untar it
2. Build mutter using clang and the coverity tool
3. Compress the coverity report
4. Upload for analysis
Things to note:
- Analysis are throttled, as per https://scan.coverity.com/faq#frequency
we qualify for 21 weekly builds, 3 daily. Mutter is sometimes a busy
project, so it seems we'd get often those consumed early in the day.
This is something we can resign to, but the times we'll try to upload
a report to have it rejected make the operation kinda pointless and
probably better throttled by ourselves.
- The task is manual, given the restrictions above.
- The task only applies on master, as the envvar holding the coverity
token is protected in gitlab.
- I had to use clang as the coverity tool doesn't seem to work ATM with
gcc as per recent Fedora.
- The coverity tarball is 1.2GB in size, which is a bit too big to have
it downloaded each time. As per their upload instructions, the tarball
gets updated twice yearly, so this is cached to minimize downloads.
- The coverity token for mutter is kept private/hidden in gitlab CI
settings.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1100>
Not sure how to update the damage or redraw clip or something; at least
this works properly when under a constantly-redrawing window, which is
ok for debugging purposes.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1762>
Max render time shows how early the frame clock needs to be dispatched
to make it to the predicted next presentation time. Before this commit
it was set to refresh interval minus 2 ms. This means Mutter would
always start compositing 14.7 ms before a display refresh on a 60 Hz
screen or 4.9 ms before a display refresh on a 144 Hz screen. However,
Mutter frequently does not need as much time to finish compositing and
submit buffer to KMS:
max render time
/------------\
---|---------------|---------------|---> presentations
D----S D--S
D - frame clock dispatch
S - buffer submission
This commit aims to automatically compute a shorter max render time to
make Mutter start compositing as late as possible (but still making it
in time for the presentation):
max render time
/-----\
---|---------------|---------------|---> presentations
D----S D--S
Why is this better? First of all, Mutter gets application contents to
draw at the time when compositing starts. If new application buffer
arrives after the compositing has started, but before the next
presentation, it won't make it on screen:
---|---------------|---------------|---> presentations
D----S D--S
A-------------X----------->
^ doesn't make it for this presentation
A - application buffer commit
X - application buffer sampled by Mutter
Here the application committed just a few ms too late and didn't make on
screen until the next presentation. If compositing starts later in the
frame cycle, applications can commit buffers closer to the presentation.
These buffers will be more up-to-date thereby reducing input latency.
---|---------------|---------------|---> presentations
D----S D--S
A----X---->
^ made it!
Moreover, applications are recommended to render their frames on frame
callbacks, which Mutter sends right after compositing is done. Since
this commit delays the compositing, it also reduces the latency for
applications drawing on frame callbacks. Compare:
---|---------------|---------------|---> presentations
D----S D--S
F--A-------X----------->
\____________________/
latency
---|---------------|---------------|---> presentations
D----S D--S
F--A-------X---->
\_____________/
less latency
F - frame callback received, application starts rendering
So how do we actually estimate max render time? We want it to be as low
as possible, but still large enough so as not to miss any frames by
accident:
max render time
/-----\
---|---------------|---------------|---> presentations
D------S------------->
oops, took a little too long
For a successful presentation, the frame needs to be submitted to KMS
and the GPU work must be completed before the vblank. This deadline can
be computed by subtracting the vblank duration (calculated from display
mode) from the predicted next presentation time.
We don't know how long compositing will take, and we also don't know how
long the GPU work will take, since clients can submit buffers with
unfinished GPU work. So we measure and estimate these values.
The frame clock dispatch can be split into two phases:
1. From start of the dispatch to all GPU commands being submitted (but
not finished)—until the call to eglSwapBuffers().
2. From eglSwapBuffers() to submitting the buffer to KMS and to GPU
work completing. These happen in parallel, and we want the latest of
the two to be done before the vblank.
We measure these three durations and store them for the last 16 frames.
The estimate for each duration is a maximum of these last 16 durations.
Usually even taking just the last frame's durations as the estimates
works well enough, but I found that screen-capturing with OBS Studio
increases duration variability enough to cause frequent missed frames
when using that method. Taking a maximum of the last 16 frames smoothes
out this variability.
The durations are naturally quite variable and the estimates aren't
perfect. To take this into account, an additional constant 2 ms is added
to the max render time.
How does it perform in practice? On my desktop with 144 Hz monitors I
get a max render time of 4–5 ms instead of the default 4.9 ms (I had
1 ms manually configured in sway) and on my laptop with a 60 Hz screen I
get a max render time of 4.8–5.5 ms instead of the default 14.7 ms (I
had 5–6 ms manually configured in sway). Weston [1] went with a 7 ms
default.
The main downside is that if there's a sudden heavy batch of work in the
compositing, which would've made it in default 14.7 ms, but doesn't make
it in reduced 6 ms, there is a delayed frame which would otherwise not
be there. Arguably, this happens rarely enough to be a good trade-off
for reduced latency. One possible solution is a "next frame is expected
to be heavy" function which manually increases max render time for the
next frame. This would avoid this single dropped frame at the start of
complex animations.
[1]: https://www.collabora.com/about-us/blog/2015/02/12/weston-repaint-scheduling/
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1762>
Scanout doesn't go through the usual path of compositing and doing
eglSwapBuffers, therefore it doesn't hit the timestamp query placed in
that path. Instead, get the timings by binding the scanout buffer to an
FBO and doing a timestamp query on the FBO.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1762>
Add utilities that allow getting the current GPU timestamp and creating
a query which completes upon completion of all operations currently
submitted on a framebuffer. Combined, these two allow measuring how long
it took the GPU to finish rendering something to a framebuffer.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1762>
