Created attachment 137332 [details]
A recording of the symptom.
This is likely related to kwin but kate is the most common one that I noticed, whenever I press Ctrl+S, the line number column has a big chance of producing a flash. Fast flashing images really makes me uncomfortable so this makes kate very difficult use for me.
STEPS TO REPRODUCE
1. Launch kate in a plasma wayland session
2. Press Ctrl+S
3. If you don't see it, press Ctrl+S again and again (but do not hold it down)
The line number column sometimes flashes.
There should be no graphical glitches.
Linux/KDE Plasma: Fedora 34, kernel 5.11.11
(available in About System)
KDE Plasma Version: 5.21.3
KDE Frameworks Version: 5.80.0
Qt Version: 5.5.2
Changing compositor rendering backends does not help with this situation, and this does not happen in x11 sessions.
I am using an RX550 with the amdgpu driver.
>Qt Version: 5.5.2
Apologies, I meant 5.15.2.
Interesting, cannot reproduce myself.
I highly suspect this is an issue with the graphics driver/graphics card but I do not have enough supporting evidence to prove it. Never had this kind of issues with i915. I don't see any error messages unfortunately.
*** Bug 436576 has been marked as a duplicate of this bug. ***
I am on Intel HD Graphics 4000 and am experiencing this bug, too.
It sounds rather unlikely to me that it would be related to the graphics card/driver, however.
This looks like a client buffer or damage related issue in kate or qtwayland. If you run kwin with KWIN_USE_BUFFER_AGE=0, for example by putting it in /etc/environment, is the issue still reproducible?
Software versions have since changed so here are the new versions:
Linux/KDE Plasma: Fedora 34, kernel 5.12.8
KDE Plasma Version: 5.21.5
KDE Frameworks Version: 5.82.0
Qt Version: 5.15.2
KWIN_USE_BUFFER_AGE=0 was placed into /etc/environment, computer was rebooted and I confirmed this variable has been set, but it's still very much reproducible just like the video showed.
Another curious thing is that having Firefox running (doesn't matter if it's xwayland or wayland native) makes this issue significantly more difficult to reproduce with keyboard presses, but I can confirm it is still present.
Additionally, I found another more effective way to reproduce this, it's holding Ctrl and keep scrolling up and down with the mouse wheel to repeatedly zoom in and out. This way I was able to reproduce this problem even with Firefox running, where it's incredibly difficult to reproduce the issue with F5 or Ctrl + S.
I confirm Alice McLafferty's statement that setting KWIN_USE_BUFFER_AGE=0 does not eliminate the visual glitches.
I can't endorse that Firefox would affect the behaviour in any way, though. It sounds rather esoteric to me.
Indeed, I have no idea why having Firefox open would affect this behavior, but it is something I have noticed on my computer. I had about four windows open in Firefox, not sure if it's reproducible with only one window open.
>This looks like a client buffer or damage related issue in kate or qtwayland.
Does to me too, moving.
Created attachment 143039 [details]
screen recording on neon unstable
I also see this bug on neon unstable. I have recorded a video showing what
happens to line number column while I create/remove lines.
I can reproduce the flashing, it occurs on resize of the widget.
The reason is the update() for the size change we trigger in the paint function after updateGeometry().
A possibly relevant merge request was started @ https://invent.kde.org/frameworks/ktexteditor/-/merge_requests/272
Git commit 61a1bee1ac286ee9e5293fd8faeb7e6162ce043a by Christoph Cullmann.
Committed on 29/01/2022 at 20:07.
Pushed by cullmann into branch 'master'.
avoid flicker for border on size changes
if you type and e.g. the line count crosses the X -> XX
border without this, a short flicker will occur
M +13 -6 src/view/kateviewhelpers.cpp
M +1 -0 src/view/kateviewhelpers.h