blur flickering on inactive windows

[illia-bobyr]

Summary

Inactive windows periodically (roughly once per second) develop a strong, full-window blur/smear effect that builds up over ~1 second and then snaps instantly back to a sharp render. This happens with blur-background = false in the config.

Reproduces on both backend = "glx" (new/default backend) and backend = "egl".
I tried switching to --legacy-backends with glx or xr_glx_hybrid, but picom crashes within ~1 second with a flood of GLX_BAD_DRAWABLE X errors instead.
If I select backend = "xrender", then the issue disappears with the same config.

Environment

• picom version: v12.5 (picom --version)
• GPU: NVIDIA RTX 3080
• NVIDIA driver version: 595.71.05
• OS: Ubuntu 26.04
• Display server: X11, session started via gdm-x-session
• Window manager: xmonad, inside a GNOME session. GNOME/Mutter is not compositing, picom is the only active compositor.

Relevant picom.conf settings

backend = "glx"
vsync = false          # also tested true, see below
use-damage = true      # also tested false, no change
xrender-sync-fence = true
unredir-if-possible = true   # also tested false, no change
blur-background = false
blur-background-frame = false
fading = false
corner-radius = 0

Shadows/fading/blur are all either disabled or visually inert in this config, and none of them affect the bug.

Steps to reproduce

1. Run picom with backend = "glx" (default new backend), config as above.
2. Watch any inactive window for 10–20 seconds.
3. Roughly once per second, the window's content develops a strong blur that peaks after about a second of buildup, then instantly reverts to a sharp, correct render.
4. At the peak, text in the window is almost unreadable.

Expected behavior

With blur-background = false, inactive windows should render statically, with no blur or distortion at any point.

Things I've tried

• Confirmed only one compositor is running - picom.
• Confirmed blur-background / blur-background-frame are false to rule out the blur engine itself as the cause.
• Tuned glx-specific options individually and in combination: vsync = true, glx-no-stencil = true, glx-no-rebind-pixmap = true, unredir-if-possible = false, use-damage = false (no-use-damage = true). None changed the behavior.
• Switched to backend = "egl". Same periodic corruption as glx.
• Switched to backend = "xrender". Issue completely resolved, no artifacts.
• Ran with --legacy-backends and backend = "glx". This crashes within ~1 second, console flooded with hundreds of repeats of:

  [ 06/25/2026 16:57:19.993 x_handle_error WARN ] Stray X error: X error 160 GLX_BAD_DRAWABLE request 152 minor 11 serial 6629

• Ran with --legacy-backends and backend = "x r_glx_hybrid" — same crash/error pattern as legacy glx.
• Tried backend = "xr_glx_hybrid" without --legacy-backends — refuses to start:

  [ 06/25/2026 16:38:18.669 sanitize_options ERROR ] Backend "xr_glx_hybrid" is only available as part of the legacy backends.
  [ 06/25/2026 16:38:18.669 session_init FATAL ERROR ] Failed to get configuration, usually mean you have specified invalid options.
  [ 06/25/2026 16:38:18.669 main FATAL ERROR ] Failed to create new session.

• Set AllowFlipping=0 via nvidia-settings. No change to the glx-backend artifact.
• Set ForceFullCompositionPipeline=On via nvidia-settings --assign CurrentMetaMode="DPY-7: 5120x2160 @5120x2160 +0+0 {ViewPortIn=5120x2160, ViewPortOut=5120x2160+0+0, ForceFullCompositionPipeline=On}". No change.
• Checked journalctl -b | grep -i glx. NVIDIA's GLX module (libglxserver_nvidia.so, 595.71.05) loads normally.

Addition information

`picom --backend glx --diagnostics`

❯ picom --backend glx --diagnostics
[ 06/25/2026 17:31:54.228 c2_parse_target WARN ] Type specifier is deprecated. Type "c" specified on target "_GTK_FRAME_EXTENTS" will be ignored, you can remove it.
[ 06/25/2026 17:31:54.228 c2_parse_target WARN ] Type specifier is deprecated. Type "c" specified on target "_GTK_FRAME_EXTENTS" will be ignored, you can remove it.
**Version:** v12.5

### Extensions:

* Shape: Yes
* RandR: Yes
* Present: Present

### Misc:

* Use Overlay: No

* Config file specified: None
* Config file used: /home/illia/.config/picom.conf

### Drivers (inaccurate):

NVIDIA

### Backend: glx

* Driver vendors:
 * GLX: NVIDIA Corporation
 * GL: NVIDIA Corporation
* GL renderer: NVIDIA GeForce RTX 3080/PCIe/SSE2
[ 06/25/2026 17:31:54.510 egl_init WARN ] The egl backend is still experimental, use with care.

### Backend: egl

* Driver vendors:
 * EGL: NVIDIA
 * GL: NVIDIA Corporation
* GL renderer: NVIDIA GeForce RTX 3080/PCIe/SSE2

glxinfo output: https://pastebin.com/iU2Bterg

[illia-bobyr]

Here are some images of what it looks like.
What I see with xrender backend:

I change the backend parameter in ~/.config/picom.conf to glx and see something like this:

Top black bar is xmobar.
Focus is in the bottom window (Kitty terminal), but it is also getting the blur this time.
It seems to be related to the OBS recording.
When OBS is running, all windows, including the OBS window itself are getting blurry.
When OBS is off, the currently focused window does not have blur applied to it.

And here is a video of the process.
When I change the backend setting the xmobar window goes black:

picom.conf content is here: https://pastebin.com/456uKGQu