`--force-windows-fullscreen` not forcing windows to nested display size

[Kagukara]

Is there an existing issue for this?

• I have searched the existing issues

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

• The issue occurs on upstream gamescope without any modifications

Current Behavior

When running vkcube with gamescope --force-windows-fullscreen -W 3840 -H 2160 -w 3840 -h 1800 -f -- the window size of vkcube doesn't resize to the nested resolution of 3840x1800. Using mangohud the resolution of vkcube is only 500x500.

Steps To Reproduce

1. Build and install the latest commit.
2. Run in the terminal gamescope --force-windows-fullscreen -W 1920 -H 1080 -w 1920 -h 900 -f -- vkcube
   • Run with MANGOHUD=1 MANGOHUD_CONFIG=resolution to easily view the resoltion of vkcube.

Hardware information

- Distro: `Arch Linux`
- CPU: `AMD Ryzen 9 5950X 16-Core Processor`
- GPU: `AMD Radeon RX 7900 XTX (RADV NAVI31)`
- Driver Version: `Mesa 25.3.2-arch1.1`

Software information

- Desktop environment: `sway version 1.12-dev-dbe86400 (Dec 27 2025, branch 'master')`
- Session type: `wayland`
- Gamescope version: `gamescope version 3.16.19-4-g221394f (gcc 15.2.1)`
- Gamescope launch command(s): `gamescope --force-windows-fullscreen -W 3840 -H 2160 -w 3840 -h 1800 -f --`

Which gamescope backends have the issue you are reporting?

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

Logging, screenshots, or anything else

Unsure about DRM and OpenVR as I can't use them.

---

Image showing vkcube at 500x500 instead of 3840x1800.

[Kagukara]

Here's a 16:9 command I also tested with:

MANGOHUD=1 MANGOHUD_CONFIG=resolution gamescope --force-windows-fullscreen -W 3840 -H 2160 -w 1920 -h 1080 -f -- vkcube

vkcube still at 500x500.

[Kagukara]

Went through the commits and found 1ff0edc was the last working commit that had --force-windows-fullscreen working.

The build failed for 36efcfe, so I was unable to test it and --force-windows-fullscreen doesn't work in commit 81d6554 and beyond.

[mr-jovani-van-bread]

I confirm. I also had this problem, although everything worked before.