https://bugs.kde.org/show_bug.cgi?id=404966
Bug ID: 404966
Summary: Maximized transparent windows lock fps on intel
graphics
Product: kwin
Version: 5.15.2
Platform: Archlinux Packages
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: compositing
Assignee: kwin-bugs-n...@kde.org
Reporter: sawyerberge...@gmail.com
Target Milestone: ---
SUMMARY
Using Konsole (or other applications with background transparency enabled, such
as with Kvantum) with transparency enabled causes refresh rate for current
screen to be locked to 30fps.
This causes significant stuttering when switching between virtual desktops or
using any other animation.
STEPS TO REPRODUCE
1. Set konsole background transparency to value above 0
2. Enable "blur background" option in konsole color scheme
3. Enable blur effect in Desktop Effects
4. Open new konsole window
5. Full-screen or maximize konsole window
OBSERVED RESULT
current FPS measured with "Show FPS" Desktop Effect drops from 60 to locked 30
EXPECTED RESULT
FPS should stay at 60 FPS or drop gradually with increasing graphical load
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: linux 4.20.13
(available in About System)
KDE Plasma Version: 5.12.2
KDE Frameworks Version: 5.55.0
Qt Version: 5.12.1
ADDITIONAL INFORMATION
This occurs at any resolution.
This appears specific to Intel graphics (experienced on laptop with HD graphics
630, was not able to replicate with another machine with Polaris RX 480)
This appears to occur on both Wayland and X sessions.
The window does not need to be fully maximized, so long as it covers more than
2/3 of total screen area FPS drops from 60 directly to 30.
The FPS drop is not gradual, it does not scale linearly with respect to covered
area. Instead FPS drops directly and sharply from 60 to 30 when the threshold
is reached.
My GPU is not bottlenecking here (load when FPS capped at 30 is measured at a
maximum of 20 percent by intel_gpu_top from intel_gpu_tools
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