Bug 496078

Summary:	Multiple emulators like dosbox and visualboyadvance-m seem to have trouble with screen size under KDE Plasma 6 Wayland
Product:	[Plasma] kwin	Reporter:	Ellie <el>
Component:	general	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED WORKSFORME
Severity:	normal	CC:	kde, nate, ngompa13
Priority:	NOR
Version First Reported In:	6.2.2
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:
Attachments:	A copy of Dosbox apparently having trouble with centering and scaling the image properly in fullscreen An install of visualboyadvance-m seemingly having trouble with centering and scaling the image as expected

Description Ellie 2024-11-11 07:07:31 UTC

Created attachment 175723 [details]
A copy of Dosbox apparently having trouble with centering and scaling the image properly in fullscreen

SUMMARY

Multiple emulators like dosbox and visualboyadvance-m seem to have trouble with screen size under KDE Plasma 6 Wayland. When running these in full screen, only a small part of the screen is drawn as a tiny rectangle as if they detect the screen resolution completely wrong. Since it affects multiple such applications, I wonder if this is possibly some sort of KWin or Plasma bug. I attached screenshots that show the issue.

STEPS TO REPRODUCE

1. Start an affected application. This would be some Dosbox variants shipped with some https://gog.com games (might not be latest dosbox version), and https://flathub.org/apps/com.vba_m.visualboyadvance-m
2. Switch to fullscreen

OBSERVED RESULT

See screenshots, where drawn area doesn't fill the screen.

EXPECTED RESULT

Emulators fill entire screen in fullscreen, or do whatever letterboxing would be normally expected.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: postmarketOS Edge based on 3.21.0_alpha20240923, kernel 6.11.6-0-edge
KDE Plasma Version: 6.2.2
KDE Frameworks Version: 6.7.0
Qt Version: 6.7.2

ADDITIONAL INFORMATION

Comment 1 Ellie 2024-11-11 07:08:07 UTC

Created attachment 175724 [details]
An install of visualboyadvance-m seemingly having trouble with centering and scaling the image as expected

Comment 2 David Edmundson 2024-11-13 11:27:47 UTC

Probably this: https://github.com/libsdl-org/SDL/pull/11251

Uninstalling the gnome desktop portal would also fix it.

Comment 3 Ellie 2024-11-13 20:54:39 UTC

Gnome desktop portal isn't installed for me. Does this mean it's a different bug after all? However, I run both of these applications through flatpak. Would I need to uninstall it from inside the flatpak? I don't think flatpak usually offers a way of doing that, and given these flatpaks are usually depending on e.g. a GNOME environment inside even when it's KDE outside, I don't think that's a feasible solution.

I'm not entirely sure if the affected dosbox version in particular is also inside the flatpak, or rather shipped by GOG with the games. If it's the latter, this could become really convoluted to avoid for a user at the end of the day if there isn't some workaround on the host level, if I'm understanding this right.

I may have gotten something wrong though, this seems fairly involved. I hope to get some ideas on how to effectively avoid this as a user, since I don't think I can update SDL2 in this situation myself.

Comment 4 Ellie 2024-11-13 21:04:36 UTC

I also just noticed the SDL2 pull request you linked mentions "x11" in particular, while I'm using a KDE Plasma Wayland session. That made me curious, and as a test I removed the "X11 windowing system" permission of the visualboyadvance-m flatpak using flatseal and I tested it again, which to my understanding means visualboyadvance-m can now no longer use XWayland or X11 on my system and can only use native Wayland instead. After doing that, it still suffers from the same issue.  I'm not sure if that means anything or not. Sorry if it's not a relevant observation.

Comment 5 Ellie 2024-11-25 14:27:18 UTC

My deepest apologies if this is incorrect, but based on above that the pull request seems to be about X11 and I can force a wayland-only path with no XWayland involved without an improvement, I hope it's okay that I'm reopening this for now.

Comment 6 Ellie 2025-05-02 12:22:15 UTC

It seems like this problem has gone away with some recent update. Whether the update was on the KWin side or on the flatpak environment side I don't know, but I can no longer reproduce this.