[libkwineffects] Introduce API to easily show a QtQuick scene in an effect

Authored by davidedmundson on Sep 25 2019, 10:32 AM.



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.

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

Diff Detail

R108 KWin
Automatic diff as part of commit; lint not applicable.
Automatic diff as part of commit; unit tests not applicable.
Restricted Application added a project: KWin. · View Herald TranscriptSep 25 2019, 10:32 AM
Restricted Application added a subscriber: kwin. · View Herald Transcript
davidedmundson requested review of this revision.Sep 25 2019, 10:32 AM
zzag added a subscriber: zzag.EditedSep 25 2019, 11:01 AM

Bump API version in kwineffects.h

I didn't test this patch, however I think Invert effect won't be able to "invert" EffectQuickView's.

EDIT: Sorry, I just saw the last paragraph in the summary.


Mark as const


Use qCDebug.


You don't need to put whitespace after colon.


Use static_cast


stray semicolon


Style: wrong alignment of *

davidedmundson marked 5 inline comments as done.


davidedmundson marked an inline comment as done.Sep 25 2019, 11:35 AM

Tidy-up destructor

Minor documentation changes.
Add show/hide helper methods

Remove some implicit scene update calls, leave that to the responsibility of the caller

Set correct internal texture format

Probably doesn't change anything but is more technically correct

zzag accepted this revision.Sep 27 2019, 10:54 AM
zzag added inline comments.

Document this method please.

This revision is now accepted and ready to land.Sep 27 2019, 10:54 AM
This revision was automatically updated to reflect the committed changes.