When switching windows with Alt+Tab with no tabbox activated or a tabbox mode that involves the window highlight effect I can often see that parts of the inactive windows (which are half-transparent at the time) are blinking as if a couple of frames from the fade out animation are stuck in a loop. This affects only the window decoration (i.e. the decoration is blinking but not the window contents). Sometimes only portion of the decoration is blinking, but at other times the whole decoration is affected. Reproducible: Always Steps to Reproduce: 1. Disable the tabbox effect at System Settings -> Window Management -> Task Switcher. Alternatively, you can enable one of the effects that still involve the highlight effect ("Thumbnails", "Text only", "Informative", etc.). 2. Have a few open windows on the desktop. Some maximized, others not maximized at different positions and sizes. 3. Press Alt+Tab and hold Alt. Keep pressing Tab to switch between windows and look at the inactive half-transparent windows. Actual Results: The decorations of the inactive windows are blinking. Expected Results: The blinking should not be present, the window decorations should be drawn correctly for every frame. Kubuntu 15.10, x86_64, Nvidia drivers 355.11, Core i7 2600K, 980GTX, 16 GiB RAM, no swap.
I can add that the blinking can be worked around by adding "KWIN_USE_BUFFER_AGE=0" to /etc/environment, although in this case I can sometimes see some other effects on the inactive window decorations. It looks like some portions of the decorations become less transparent and maybe filled with color (I can't tell for sure as in my case the decorations are grey and the effect looks like grey rectangles on the decorations). The effect depends on the position and size of the windows - in some cases it may not appear at all.
Created attachment 95326 [details] An example of the decoration artefact You can see on the screenshot that a little right of the active KCalc window there's a grey rectangle on the underlying inactive window decoration. This sort of artefacts appear at different places as you cycle through windows.
Looks like "air-oxygen", can you reproduce either effect with the breeze decoration? Does the flicker happen *while* the highlight effect is active or afterwards (ie. when having finished tabbox selection and all windows should be opaque again)?
(In reply to Thomas Lübking from comment #3) > Looks like "air-oxygen", Yes, that's the decoration I'm using. > can you reproduce either effect with the breeze > decoration? No, it doesn't show with org.kde.breeze or org.kde.oxygen. Both these decorations are opaque, though. > Does the flicker happen *while* the highlight effect is active or afterwards > (ie. when having finished tabbox selection and all windows should be opaque > again)? I haven't seen any flickering or corruption while the windows are normal (i.e. when they are just open on the desktop or when a window is selected in the tabbox, fully opaque). I'm only seeing the effect when windows are half-transparent. The effect may appear immediately when I press and hold Alt+Tab or when I keep pressing Tab while holding Alt in the tabbox (in the latter case the set of affected windows changes when I press Tab). The effect may affect decorations of multiple windows at once - whether they have been selected previously in the tabbox or not.
kcmshell5 kwineffects disable blur and contrast effect and see whether the issue remains. if not, reenable blur and disable caching in its config - still an issue?
(In reply to Thomas Lübking from comment #5) > kcmshell5 kwineffects > disable blur and contrast effect and see whether the issue remains. > if not, reenable blur and disable caching in its config - still an issue? The flickering happens only when both Blur and the "Save intermediate rendering results" option in its settings are enabled. In all other cases there's no flickering. The "Background contrast" effect does not affect flickering.
Then we have a dupe. *** This bug has been marked as a duplicate of bug 307112 ***
(In reply to Thomas Lübking from comment #7) > Then we have a dupe. > > *** This bug has been marked as a duplicate of bug 307112 *** It says it was fixed in 5.2.0, and I'm using 5.4.2. Clearly it's not fixed yet.
No, it's not. Marting likely wanted to CCBUG and accidentally BUG'd the commit message. There's just a workaround for a particular case, but cached blurring is definitively still broken (nobody fixed it) *** This bug has been marked as a duplicate of bug 307112 ***