Bug 504349

Summary:	Wayland HDR still using 80cd/m² for Windows scRGB instead of 203cd/m² reference luminance.
Product:	[Plasma] kwin	Reporter:	Aleksandr <sanar-momot>
Component:	colour-management	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED NOT A BUG
Severity:	minor	CC:	nate, xaver.hugl
Priority:	NOR
Version First Reported In:	6.3.90
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	kscreen-doctor -o

Description Aleksandr 2025-05-16 17:30:40 UTC

Created attachment 181394 [details]
kscreen-doctor -o

SUMMARY
Wayland HDR still using 80cd/m² for Windows scRGB instead of 203cd/m² reference luminance.

Running same games with same calibration through Gamescope has correct reference target of 203 regardless of color space

STEPS TO REPRODUCE
1. Set 1000 nit peak and 203 target brightness with HDR calibration tool on desktop
2. Launch any scRGB HDR game using wayland (Control, Cyberpunk 2077)
3. Adjust in game calibration accordingly
4. See that 203 desktop brightness is clipping on brightest light sources
5. Adjust desktop brightness to 80 nits
6. Verify that highlights in game are no longer clipping.

OBSERVED RESULT

In game highlights are clipping when desktop brightness is set to 203
In game highlights are no longer clipping when desktop brightness is set to 80

EXPECTED RESULT

Correctly calibrated in game highlights not clipping when desktop brightness is set to 203

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux 6.15.0-rc6-273-tkg-eevdf
KDE Plasma Version: 6.3.90
KDE Frameworks Version: 6.14.0
Qt Version: 6.9.0

ADDITIONAL INFORMATION

Proton version used to test Wayland 
https://github.com/GloriousEggroll/proton-ge-custom/releases/tag/GE-Proton10-1

Gamescope version used to verify findings
gamescope-git-3.16.8.r1.g1f121c6e-1

Steam launch options with wayland
PROTON_ENABLE_WAYLAND=1 PROTON_ENABLE_HDR=1 mangohud %command%

Steam launch options with gamescope
DXVK_HDR=1 gamescope -f -W 2560 -H 1440 -S integer -F nearest --hdr-enabled --hdr-sdr-content-nits 1000 --force-grab-cursor --rt --mangoapp -- %command%

Comment 1 Aleksandr 2025-05-16 18:04:50 UTC

Just discovered that using these options results in correct reference of 203cd/m²
PROTON_ENABLE_WAYLAND=1 PROTON_ENABLE_HDR=1 mangohud %command% 

And using these results in incorrect reference of 80cd/m²
DISPLAY= DXVK_HDR=1 mangohud %command% --launcher-skip

Comment 2 Zamundaaa 2025-05-19 15:17:29 UTC

Proton doesn't use Windows scRGB, gamescope is currently its only user.