Bug 458758

Summary:	Cursor duplicates in LibreOffice when global scaling is 200% or more
Product:	[Plasma] kwin	Reporter:	Jackson <bugs>
Component:	general	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED DOWNSTREAM
Severity:	normal	CC:	nate
Priority:	NOR
Version First Reported In:	5.25.4
Target Milestone:	---
Platform:	Other
OS:	Linux
URL:	https://bugs.documentfoundation.org/show_bug.cgi?id=145816#c10
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	Screenshot showing multiple cursors. Screen recording of duplicate cursors appearing.

Description Jackson 2022-09-05 18:42:17 UTC

Created attachment 151854 [details]
Screenshot showing multiple cursors.

SUMMARY
When KDE's global scaling is set to 200% or more (but not less), duplicate cursors appear in LibreOffice (Writer, Calc, etc.). 

Apologies if this is not filed in the correct place. I'm not sure of the components that would affect this, and I'm unsure if this is a KDE or a LibreOffice bug (see additional information for why).

STEPS TO REPRODUCE
1. Set global scale (Settings -> Display Configuration) to 200% or more.
2. Open a document in LibreOffice Writer (or spreadsheet in Calc, etc.).
3. Type and make some new lines.
4. Click repeatedly on the other lines.

OBSERVED RESULT
The cursor moves where the mouse is clicked, but at times leaves an image of the cursor where it was (not always, but frequently). Multiple cursors can therefore be visible on screen at once.

At times the "ghost" cursor can be seen when the cursor is just sitting there blinking (i.e., the cursor is always displayed and does not blink on and off). This makes editing documents very frustrating.

EXPECTED RESULT
The cursor only appears where it is currently located. It blinks on and off.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Kubuntu 22.04
(available in About System)
KDE Plasma Version: 5.25.4
KDE Frameworks Version: 5.95.0
Qt Version: 5.15.3
LibreOffice: 7.3.5.2

ADDITIONAL INFORMATION
This occurs on any display I've tested (4K laptop screen of a ThinkPad X1 Carbon Gen 7, 1600x900 laptop screen of a ThinkPad T420s, 2K and 1080p monitors of a desktop with an Intel i7 CPU and integrated graphics), and it happens in both X11 and Wayland. Tested in Kubuntu as above, but also KDE Neon testing branch (Plasma 5.25.4; Frameworks 5.98.0; Qt 5.15.5), and Manjaro (Plasma 5.24.6; Frameworks 5.96.0; Qt 5.15.5). 

At first I thought this was a LibreOffice bug, since I have only encountered this issue there and in no other program. Indeed, this does not occur in the older 6.4 series of LibreOffice, only the newer 7 series. The relevant bug in their tracker is here: https://bugs.documentfoundation.org/show_bug.cgi?id=145816

However, the bug does not occur in Gnome. With global scaling set to 200% or 300%, all versions of LibreOffice, including the newest 7 series, display the cursor correctly and no ghosting occurs.

Hopefully someone who knows more than I do can figure out what is causing this, and apologies again if this is incorrectly filed.

Comment 1 Jackson 2022-09-05 18:42:57 UTC

Created attachment 151855 [details]
Screen recording of duplicate cursors appearing.

Comment 2 Nate Graham 2022-09-09 03:57:50 UTC

How bizarre. Cannot reproduce with git master KWin Wayland and LibreOffice 7.3.4.2 on Fedora 36.

Comment 3 Jackson 2022-09-17 20:03:48 UTC

(In reply to Nate Graham from comment #2)
> How bizarre. Cannot reproduce with git master KWin Wayland and LibreOffice
> 7.3.4.2 on Fedora 36.

It looks like the issue is with LibreOffice's "kf5" VCL plugin, finally narrowed down here: https://bugs.documentfoundation.org/show_bug.cgi?id=145816#c10. 

If LibreOffice is set to use the GTK VCL plugin, the cursor issue does not occur (unfortunately that means stuff like the KDE file picker isn't used, toolbar icons are blurry, etc.). Maybe Fedora 36 uses the gtk3 integration by default?