Bug 348455

Summary:	Blur & contrast shaders cause flicker on intel i915
Product:	[Plasma] kwin	Reporter:	Pierre Ducroquet <pinaraf>
Component:	effects-various	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED WORKSFORME
Severity:	normal	CC:	arojas
Priority:	NOR	Flags:	thomas.luebking: Intel+
Version First Reported In:	5.3.0
Target Milestone:	---
Platform:	Fedora RPMs
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Pierre Ducroquet 2015-05-30 14:26:15 UTC

GPU : IGP from Atom N270 platform, so old i915 GPU
In most situations, the compositing works perfectly, but in some specific cases like the logout screen and its fading background animation (sometimes overlapping windows seem to be enough, but not always…), there is heavy flickering on the screen.
Compositing is done with the OpenGL 2 mode. Switching to XRender solves the issue.
If needed, I can send a video of the issue.

Comment 1 Thomas Lübking 2015-05-30 18:42:46 UTC

Smells like the blur shader being the ultimate trigger.

Could you add/override

[Effect-Logout]
UseBlur=false

in ~/.config/kwinrc

and disable the blur (and likely the "contrast") effect in the dialog spawned by "kcmshell5 kwineffects" and check the result?

Comment 2 Pierre Ducroquet 2015-05-31 14:16:26 UTC

Indeed, this "fixes" the issue. And the contrast effect creates flickering when switching between windows using alt-tab.

By the way, if you need the OpenGL renderer and version strings to identify the GPU :
renderer : Mesa DRI Intel(R) 945GME
version : 2.1 Mesa 10.5.4

Comment 3 Thomas Lübking 2015-05-31 14:56:40 UTC

For a wild shot, re-enable the effect(s) and run

export KWIN_USE_INTEL_SWAP_EVENT=0 # should be disabled anyway
export KWIN_USE_BUFFER_AGE=0
kwin_x11 --replace &


Does this also happen with the EGL backend?

Comment 4 Antonio Rojas 2015-09-04 09:04:16 UTC

This has gotten much worse with linux 4.2. With linux <4.2 this happened for me after almost every restart, but restarting kwin was enough to fix it for the entire session. Now restarting kwin only fixes it for a shot time (less than 1 minute). 

Still happens with
export KWIN_USE_INTEL_SWAP_EVENT=0
export KWIN_USE_BUFFER_AGE=0

Comment 5 Thomas Lübking 2015-09-04 13:09:33 UTC

Try https://wiki.archlinux.org/index.php/Intel_graphics#SNA_issues
Also please attach the output of "qdbus org.kde.KWin /KWin supportInformation"

This very bug was caused by the blur shader (in the logout effect) which doesn't really fit your description - however, I assume this is due to the blur & contrast shaders?

Comment 6 Vlad Zahorodnii 2018-10-21 19:57:22 UTC

Works fine for me.

If you're still able to reproduce the bug, please reopen this bug report.