Bug 512663

Summary:	Flickering on the episode info page
Product:	[Applications] kasts	Reporter:	fabinho17
Component:	general	Assignee:	bart
Status:	REPORTED ---
Severity:	normal
Priority:	NOR
Version First Reported In:	25.08.3
Target Milestone:	---
Platform:	Flatpak
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	Video showing the episode details view in kasts flickering

Description fabinho17 2025-11-27 06:11:34 UTC

Created attachment 187202 [details]
Video showing the episode details view in kasts flickering

SUMMARY
The Episode Details view continuously flickers for certain podcasts when the window is in the maximized state.

STEPS TO REPRODUCE
1. Open episode detials for a recent episode from the "Linux Matters" podcast (https://linuxmatters.sh/episode/index.xml)
2. Maximize the window

OBSERVED RESULT
UI within the episode detials view continuously flickers, scrollbar disapears which is possibly related

EXPECTED RESULT
UI should be displayed stably

SOFTWARE/OS VERSIONS
Using the flatpak on GNOME Wayland
mutter, gnome-shell: 49.2
KDE Plasma Version: KDE flatpak runtime v6.10
KDE Frameworks Version: 6.19.0
Qt Version: 6.10.0

ADDITIONAL INFORMATION
Attaching video. The window is being maximized even though the size remains the same as the video is scaled to the window size.

Comment 1 fabinho17 2025-11-27 06:30:24 UTC

Sorry, I completely forgot that I had set the env variable "QT_SCALE_FACTOR=1.15" through flatpak. The glitch doesn't happen if I unset it. Please close the issue if this is unsupported. Also, if there is a proper way to scale the UI in a flatpak then that would be good to know.

Comment 2 bart 2025-11-27 08:52:45 UTC

I honestly also don't know what to expect with those settings inside a flatpak.
I know that the fractional scaling seems to work relatively well with e.g. 1.25 or 1.5 (not inside flatpak). I haven't tried 1.15, though.
But, regardless, there is not much that apps can do about this; this is built-in functionality of the toolkit (i.e. qt).

If you can reproduce the issue (perhaps also on other qt apps), you could always file a bug report against Qt upstream.

Thanks for reporting anyway. It's good to know what is broken, even if it's upstream and out of our hands.

Comment 3 fabinho17 2025-11-27 11:19:57 UTC

(In reply to bart from comment #2)
> I know that the fractional scaling seems to work relatively well with e.g.
> 1.25 or 1.5 (not inside flatpak). I haven't tried 1.15, though.
Thanks for replying promptly. I tried 1.25 and the flickering went away. I guess sticking to factors of 0.25 should be fine.
> If you can reproduce the issue (perhaps also on other qt apps), you could
> always file a bug report against Qt upstream.
Unfortunately, Kasts is the only qt app I use regularly. I tried 1.15 with the qpwgraph flatpak and that's working fine on a quick glance. Its hard to replicate the exact bug in other apps as even with Kasts the bug only happens with the episode details view on certain podcasts only.
> Thanks for reporting anyway. It's good to know what is broken, even if it's
> upstream and out of our hands.
Happy to help in any way. I'll leave the decision to close this to you. I'm comfortable with using 1.25 scaling.