Fullscreen doesn't pillarbox games in fullscreen mode on KDE 6.2

[KayJay7]

Is there an existing issue for this?

• [X] I have searched the existing issues

Are you using any gamescope patches or a forked version of gamescope?

• [X] The issue occurs on upstream gamescope without any modifications

Current Behavior

The main way I use gamescope is to force pillarboxing on games that need it but don't implement it (e.g. Terraria). I cannot pinpoint when it happened (but I can tell it worked in June) but now gamescope doesn't pillarbox anymore, it just shows the game windows in the upper left corner of the screen, like if it was just a borderless window that doesn't cover the whole screen.

Examples:

I do not think it's an issue with kde, because other fullscreen applications work correctly with pillarboxing. For example, here is Quantum Break in fullscreen pillarboxed:

I have tried both the Wayland and SDL backend, but for some reason the SDL one fails to start. Also, I have tried various combination of commands: with different -S parameters, with -b etc. I'm reporting one of the simpler ones

For some reason, I'm not able to replicate the issue on vkcube or glxgears from terminal. I'm running gamescope -h 100 -w 100 -W 2560 -H 1080 -S integer -F pixel -f -- vkcube and it works as expected. It scales to 1000x1000 and adds black borders.

Steps To Reproduce

1. Launch Terraria from Steam with gamescope -h 1080 -w 1920 -H 1080 -W 2560 -f -- %command% on latest KDE
   • The nested resolution needs to be smaller than the real resolution
2. The game window will not be pillarboxed correctly

Hardware information

- Distro: Fedora 40
- CPU: AMD Ryzen R7 7700x
- GPU: AMD Radeon Vega 56
- Driver Version: Mesa 24.1.7

Software information

- Desktop environment: KDE 6.2.2
- Session type: Wayland
- Gamescope version: ?
	* The output of `gamescope --version` is missing the version number `gamescope version  (gcc 14.2.1)`
	* Dnf reports version 3.15.13
- Gamescope launch command(s): `gamescope -h 1080 -w 1920 -H 1080 -W 2560 -f -- %command%`

Which gamescope backends have the issue you are reporting?

• [X] Wayland (default for nested gamescope)
• [ ] DRM (default for embedded gamescope, i.e. gamescope-session)
• [ ] SDL
• [ ] OpenVR

Logging, screenshots, or anything else

Same screenshot as before:

It even causes a weird effect with mangohud where it overflows from the window, while usually it's cropped at the window borders