Bug 497378

Summary:	"Selection rectangle" on desktop lagging behind mouse cursor, and very glitchy desktop icons when moved
Product:	[Plasma] plasmashell	Reporter:	John <sigmund.haydin>
Component:	Desktop icons & Folder View widget	Assignee:	Plasma Bugs List <plasma-bugs>
Status:	CLOSED DUPLICATE
Severity:	minor	CC:	hein, kdedev, nate
Priority:	NOR
Version First Reported In:	master
Target Milestone:	1.0
Platform:	Debian stable
OS:	Linux
See Also:	https://bugs.kde.org/show_bug.cgi?id=403653
Latest Commit:		Version Fixed In:
Sentry Crash Report:

Description John 2024-12-12 16:34:39 UTC

Ever since switching to Linux and settling for KDE Plasma as the DE, I've experienced two frustrating and persistent performance bugs on the desktop, most likely closely related:

1. When clicking on the desktop and making a "selection rectangle", it very noticeably "lags behind" the mouse cursor's position (in a smooth animation -- the actual drawing of the rectangle does not itself lag).
2. When moving icons around on the desktop, they are very "heavy", unresponsive and glitchy. Unless I carefully place the mouse cursor over an icon, click and then slowly move it to the new location, the mouse cursor and the icon get "detached" from each other.

This happens even with a completely fresh installation, right away, with no system load, on both Debian 12 (Plasma 5) and their "Debian Live" environment which has Plasma 6 and updated drivers.

It has happened on two separate (powerful) PCs, with three different GPU architectures: NVIDIA (earliest attempts), AMD and (the new one) Intel GPU.

The only way for me to be able to use the system at all is to run `kcmshell5 kcm_qtquicksettings` and switch the "Rendering backend" option from "Auto" to "software" and reboot. If I do that, it's possible to use the desktop, but it's still far from working correctly. The selection rectangle still isn't fully following the mouse cursor even in this mode and the icons still act up in the same manner randomly.

On both machines, all other parts of the Plasma GUI work correctly. Nothing about the window management or applications menu etc. strikes me as being laggy or glitchy. This issue seems fully contained to the "desktop" area, which unfortunately is a "main workspace" for me and (I would assume) most other users. I cannot understand how this is technically possible.

I have tried many things suggested by many people over an extended period of time. Some fresh attempts from today:

* The note on https://wiki.debian.org/GraphicsCard#Intel which says to remove the xserver-xorg-video-intel package doesn't help. The issue remains even after doing that, turning the "Rendering backend" back to "Auto" and rebooting.
* Trying out Fedora-KDE-Live-x86_64-41-1.4.iso reveals that the selection rectangle lag still happens on that different distro, although to a lesser degree. The icons, however, seem much snappier/responsive here, so it does seem to in some way be related to something that Debian does differently?

It's not an option for me to switch to a different Linux distro. I don't understand how it can depend on the distro, when it's the same KDE Plasma software and OS. It would be very interesting to learn what is causing this.

The new computer's CPU (with built-in GPU) is an Intel Core I9 14900. If that's "too new" to be fully supported by Linux, it still doesn't explain how the same problems happen on the 5+ year old HP workstation. I was prepared to believe that the old one was simply broken somehow on a hardware level, until I experienced the same issues on the new one.

Hopefully I've managed to include all relevant information.

Comment 1 TraceyC 2024-12-12 17:06:38 UTC

Thanks for the bug report. Can you please let us know: are you seeing this in a Wayland session or X11 session or both?

Comment 2 Nate Graham 2024-12-12 17:25:50 UTC

The icon glitching is a GPU driver issue of some sort, not a bug in our code, so let's focus on the selection rectangle issue.

Comment 3 Nate Graham 2024-12-12 17:26:41 UTC

And that's already tracked by Bug 388808. I thought I remembered an existing bug report for it.

*** This bug has been marked as a duplicate of bug 388808 ***

Comment 4 John 2024-12-12 20:56:56 UTC

(In reply to TraceyC from comment #1)
> Thanks for the bug report. Can you please let us know: are you seeing this
> in a Wayland session or X11 session or both?

I knew I forgot something important!

X11.

(When I tried Wayland on the Debian Live environment, it resulted in a black screen with just the mouse cursor moving. But I don't need Wayland to work for my use for the foreseeable future -- just mentioning it.)

Comment 5 John 2024-12-12 20:58:25 UTC

(In reply to Nate Graham from comment #2)
> The icon glitching is a GPU driver issue of some sort, not a bug in our
> code, so let's focus on the selection rectangle issue.

A GPU driver issue in both NVIDIA, AMD and Intel GPU drivers on two separate machines? That's literally all the "brands" of GPUs in existence for the consumer market. (Known to me at least.)

Comment 6 John 2024-12-12 20:59:52 UTC

(In reply to Nate Graham from comment #3)
> And that's already tracked by Bug 388808. I thought I remembered an existing
> bug report for it.
> 
> *** This bug has been marked as a duplicate of bug 388808 ***

Why did you mark this as "resolved" when it hasn't been resolved at all? Nor is it a duplicate of that other bug, which also hasn't been resolved.

I also notice that my report has been downgraded to "minor". What's going on here?

Comment 7 Nate Graham 2024-12-12 21:02:27 UTC

(In reply to John from comment #6)
> Why did you mark this as "resolved" when it hasn't been resolved at all? Nor
> is it a duplicate of that other bug, which also hasn't been resolved.

Please read https://community.kde.org/Get_Involved/Issue_Reporting#Understand_what_the_resolution_statuses_mean

> I also notice that my report has been downgraded to "minor". What's going on
> here?

Because the selection rectangle *is* a minor issue; it's cosmetic only.

The icon issue is something else, like I said probably a graphics issue of some sort, but regardless, it's inappropriate to bring it up in this specific bug report since bug reports need to be about only one issue, not multiple issues.

Comment 8 John 2024-12-12 21:06:39 UTC

(In reply to Nate Graham from comment #7)
> (In reply to John from comment #6)
> > Why did you mark this as "resolved" when it hasn't been resolved at all? Nor
> > is it a duplicate of that other bug, which also hasn't been resolved.
> 
> Please read
> https://community.kde.org/Get_Involved/
> Issue_Reporting#Understand_what_the_resolution_statuses_mean
> 
> > I also notice that my report has been downgraded to "minor". What's going on
> > here?
> 
> Because the selection rectangle *is* a minor issue; it's cosmetic only.
> 
> The icon issue is something else, like I said probably a graphics issue of
> some sort, but regardless, it's inappropriate to bring it up in this
> specific bug report since bug reports need to be about only one issue, not
> multiple issues.

The two things seem very much related, which is why I made them into one report. Otherwise I'd have complaints about "making too many reports" or something.

But what exactly does it mean that it's a "graphics issue"? Or rather, if Plasma's code isn't wrong after all, where lies the problem?

Comment 9 John 2024-12-12 21:08:03 UTC

(In reply to Nate Graham from comment #7)
> Because the selection rectangle *is* a minor issue; it's cosmetic only.

The cosmetic-only, minor issue which has prevented me from using my computer properly for many, long months of trying to hunt down the cause of this problem.

Comment 10 TraceyC 2024-12-13 15:39:05 UTC

The selection rectangle issue has been fixed in Plasma 6.3.0. You will see this improvement on your system when it updates to that version. If you still see the issue when your system has updated to 6.3.0, feel free to reopen this issue.

For any other outstanding issues, please open a new bug report. Thanks for your understanding.

*** This bug has been marked as a duplicate of bug 388808 ***