Summary:
EffectQuickView/Scene is a convenient class to render a QtQuick
scenegraph into an effect.
Current methods (such as present windows) involve creating an underlying
platform window which is expensive, causes a headache to filter out
again in the rest of the code, and only works as an overlay.
The new class exposes things more natively to an effect where we don't
mess with real windows, we can perform the painting anywhere in the view
and we don't have issues with hiding/closing.
QtQuick has both software and hardware accelerated modes, and kwin also
has 3 render backends. Every combination is supported.
* When used in OpenGL mode for both, we render into an FBO export the
texture ID then it's up to the effect to render that into a scene.
* When using software QtQuick rendering we blit into an image, upload
that into a KWinGLTexture which serves as an abstraction layer and
render that into the scene.
* When using GL for QtQuick and XRender/QPainter in kwin everything is
rendered into the internal FBO, blit and exported as an image.
* When using software rendering for both an image gets passed directly.
Mouse and keyboard events can be forwarded, only if the effect
intercepts them.
The class is meant to be generic enough that we can remove all the
QtQuick code from Aurorae.
The intention is also to replace EffectFrameImpl using this backend and
we can kill all of the EffectFrame code throughout the scenes.
The close button in present windows will also be ported to this,
simplifiying that code base.
Classes that handle the rendering and handling QML are intentionally
split so that in the future we can have a declarative effects API create
overlays from within the same context. Similar to how one can
instantiate windows from a typical QML scene.
Notes:
I don't like how I pass the kwin GL context from the backends into the
effect, but I need something that works with the library separation. It
also currently has wayland problem if I create a QOpenGLContext before
the QPA is set up with a scene - but I don't have anything better?
I know for the EffectFrame we need an API to push things through the
effects stack to handle blur/invert etc. Will deal with that when we
port the EffectFrame.
Test Plan: Used in an effect
Reviewers: #kwin, zzag
Reviewed By: #kwin, zzag
Subscribers: zzag, kwin
Tags: #kwin
Differential Revision: https://phabricator.kde.org/D24215
KWin is an easy to use, but flexible, composited Window Manager for Xorg windowing systems (Wayland, X11) on Linux. Its primary usage is in conjunction with a Desktop Shell (e.g. KDE Plasma Desktop). KWin is designed to go out of the way; users should not notice that they use a window manager at all. Nevertheless KWin provides a steep learning curve for advanced features, which are available, if they do not conflict with the primary mission. KWin does not have a dedicated targeted user group, but follows the targeted user group of the Desktop Shell using KWin as it's window manager.
KWin is not...
a standalone window manager (c.f. openbox, i3) and does not provide any functionality belonging to a Desktop Shell.
a replacement for window managers designed for use with a specific Desktop Shell (e.g. GNOME Shell)
a minimalistic window manager
designed for use without compositing or for X11 network transparency, though both are possible.
If you are an application developer having questions regarding windowing systems (either X11 or Wayland) please do not hesitate to contact us. Preferable through our mailing list. Ideally subscribe to the mailing list, so that your mail doesn't get stuck in the moderation queue.
End user
Please contact the support channels of your Linux distribution for user support. The KWin development team does not provide end user support.
Please refer to hacking documentation for how to build and start KWin. Further information about KWin's test suite can be found in TESTING.md.
Guidelines for new features
A new Feature can only be added to KWin if:
it does not violate the primary missions as stated at the start of this document
it does not introduce instabilities
it is maintained, that is bugs are fixed in a timely manner (second next minor release) if it is not a corner case.
it works together with all existing features
it supports both single and multi screen (xrandr)
it adds a significant advantage
it is feature complete, that is supports at least all useful features from competitive implementations
it is not a special case for a small user group
it does not increase code complexity significantly
it does not affect KWin's license (GPLv2+)
All new added features are under probation, that is if any of the non-functional requirements as listed above do not hold true in the next two feature releases, the added feature will be removed again.
The same non functional requirements hold true for any kind of plugins (effects, scripts, etc.). It is suggested to use scripted plugins and distribute them separately.
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