https://bugs.kde.org/show_bug.cgi?id=526226
Bug ID: 526226
Summary: Resizing windows lags proportionally with window size
with certain window types/applications
Classification: Plasma
Product: kwin
Version First 6.7.5
Reported In:
Platform: NixOS
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: performance
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
DESCRIPTION
Resizing certain windows lags the desktop considerably on a high resolution
monitor as the resized window size grows.
Seems to affect only some windows/applications. For example, most if not all
KDE Applications (e.g. Kate, System Settings, Dolphin) seem to suffer from
this. Any Qt6 and GTK apps I have tested so far seem to suffer.
I also tried compiling a couple minimal Qt6 and GTK4 C++ programs respectively
that just launch a single window with nothing in it. Both exhibit this lag, in
native wayland as well as X11/xwayland.
Some unaffected programs: Discord and VSCode (Electron-based), Fluffychat
(Flutter-based), Firefox, Chromium.
The lower (smaller) the display scale, the worse the performance.
STEPS TO REPRODUCE
1. On a relatively high-resolution (4k or above) display, 100% display scaling:
2. Start Kate or some other suitable minimal program that suffers from this
(see above)
3. Position the window on the top-left and start dragging the bottom right
corner to resize
OBSERVED RESULT
- When the window is smaller (e.g. quarter display size / 1080p or below), the
mouse cursor and widow resizing animation are both smooth, at or close to full
display refresh rate
- As the widow is stretched close to to the full monitor size, performance
plummets. Both the mouse cursor and window animation start lagging
significantly.
- On a 165Hz 5120x2160 display running on an AMD Radeon PRO R9700, the desktop
can go from a smooth 165fps at small window sizes to approx. 5-10fps when the
window is near full display size.
EXPECTED RESULT
The desktop animation and cursor should stay relatively performant regardless
of the size of the window being resized. There should be no significant
difference in performance when resizing for example a large Chromium vs a large
Kate window.
SOFTWARE/OS VERSIONS
Operating System (available in the Info Center app, or by running `kinfo` in a
terminal window):
KDE Plasma Version: 6.7.5
KDE Frameworks Version: 6.30.0
Qt Version: 6.11.2
ADDITIONAL INFORMATION
Kernel version: 7.2.6
Graphics Platform: Wayland
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