Some users reported performances issues after recent compositing
scheduling changes, in particular animations being laggy.
The issue is that sometimes it may take more than a vblank interval for
a buffer swap to complete. Previously, compositing was driven by a
timer and it wasn't synchronized to vblanks. If some frame is running
late, the compositor will just start painting a new frame, i.e. the
screen will be rendered triple buffered.
This change disables the swap events code path on Intel to restore the
previous behavior. Unfortunately, that may add an extra frame of latency.
The swap events code path can be enabled explicitly on Intel by setting
the KWIN_USE_INTEL_SWAP_EVENT environment variable to 1.
Warning messages are not the kind of messages that should be ignored,
they indicate that something is off or wrong.
Also, this makes triaging bugs easier as we no longer have to ask people
to run kwin with the QT_LOGGING_RULES environment variable set.
With the new compositing scheduling, we want the screen to be redrawn as
close as possible to the next vblank. Furthermore, compositing is no
longer driven by a timer. This change removes the NoSwapEncourage swap
strategy as it doesn't make sense now, in addition to that it just does
not work on Wayland.
At the moment, our frame scheduling infrastructure is still heavily
based on Xinerama-style rendering. Specifically, we assume that painting
is driven by a single timer, etc.
This change introduces a new type - RenderLoop. Its main purpose is to
drive compositing on a specific output, or in case of X11, on the
overlay window.
With RenderLoop, compositing is synchronized to vblank events. It
exposes the last and the next estimated presentation timestamp. The
expected presentation timestamp can be used by effects to ensure that
animations are synchronized with the upcoming vblank event.
On Wayland, every outputs has its own render loop. On X11, per screen
rendering is not possible, therefore the platform exposes the render
loop for the overlay window. Ideally, the Scene has to expose the
RenderLoop, but as the first step towards better compositing scheduling
it's good as is for the time being.
The RenderLoop tries to minimize the latency by delaying compositing as
close as possible to the next vblank event. One tricky thing about it is
that if compositing is too close to the next vblank event, animations
may become a little bit choppy. However, increasing the latency reduces
the choppiness.
Given that, there is no any "silver bullet" solution for the choppiness
issue, a new option has been added in the Compositing KCM to specify the
amount of latency. By default, it's "Medium," but if a user is not
satisfied with the upstream default, they can tweak it.
EGL for X and EGL for Wayland backends are quite different. The main
motivation behind this change is to prepare the EGL backends for
monitoring vblank events. Things work quite differently depending on
if the EGL backend renders onto a toplevel window or overlay window.
With the new compositing timing, we want to start compositing some time
later after a vsync event. This doesn't go along with the video sync
based method to synchronize buffer swaps with vblank.
Since practically all drivers nowadays provide support for the swap
control extensions (GLX_EXT_swap_control, GLX_SGI_swap_control, or
GLX_MESA_swap_control), it's safe to rely on them for the purpose of
synchronizing buffer swaps to vblank.
The compositing timing algorithm assumes that glXSwapBuffers() and
eglSwapBuffers() block. While this was true long time ago with NVIDIA
drivers, nowadays, it's not the case. The NVIDIA driver queues
several buffers in advance and if the application runs out of them,
it will block. With Mesa driver, swapping buffer was never blocking.
This change makes the render backends swap buffers right after ending
a compositing cycle. This may potentially block, but it shouldn't be
an issue with modern drivers. In case it gets proven, we can move
glXSwapBuffers() and eglSwapBuffers() in a separate thread.
Note that this change breaks the compositing timing algorithm, but
it's already sort of broken with Mesa drivers.
Since the Screens class is a convenience wrapper around AbstractOutput
objects that come from the Platform, it should not be platform-specific.
By dropping createScreens(), output-related code becomes simpler.
The default implementation of Screens::displaySize() returns the
bounding rectangle of all available outputs.
In case the Xrandr extension is unavailable, there will be a fake
output whose dimensions are the same as the dimensions of all screens
combined.
These signals can be useful if you want to know what output exactly has
been disabled or enabled.
The outputEnabled signal is emitted after the outputAdded signal, and
the outputDisabled signal is emitted before the outputRemoved signal.
This change moves the XRender backend to platformsupport directory,
similar to the OpenGL and the QPainter backend. This allows to put
platform-specific logic in XRenderBackend.
At the moment, the gbm_device for the primary device is destroyed before
the EGLDisplay is destroyed. This results in a crash in Mesa.
In order to fix the crash, this change ensures that the EGLDisplay is
destroyed before the gbm device.
Currently, the OpenGLBackend and the QPainterBackend have hooks to
indicate the start and the end of compositing cycle, but in both cases,
the hooks have different names. This change fixes that inconsistency.
In order to allow per screen rendering, we need the Compositor to be
able to drive rendering on each screen. Currently, it's not possible
because Scene::paint() paints all screen.
With this change, the Compositor will be able to ask the Scene to paint
only a screen with the specific id.
At the moment, despite the protocol supporting it, we were not feeding
the EDIDs. KScreen was falling back to the output name so it didn't fail
horribly but it's still a good idea to provide all the data.
If a cursor animation is driven purely by frame callbacks and kwin
uses hardware cursors, the cpu usage may spike to 100%.
This change addresses that issue by sending frame callbacks after a
compositing cycle has been performed.
This change replaces the remaining usages of the old connect syntax with
the new connect syntax.
Unfortunately, there are still places where we have to use SIGNAL() and
SLOT() macros, for example the stuff that deals with d-bus business.
Clazy was used to create this change. There were a few cases that needed
manual intervention, the majority of those cases were about resolving
ambiguity caused by overloaded signals.
The main advantage of SPDX license identifiers over the traditional
license headers is that it's more difficult to overlook inappropriate
licenses for kwin, for example GPL 3. We also don't have to copy a
lot of boilerplate text.
In order to create this change, I ran licensedigger -r -c from the
toplevel source directory.
