mne-qt-browser
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mne-tools
Some operations are extremely slow on Wayland
Description of the problem
Some operations like dragging the rectangle in the overview bar or dragging a scrollbar indicator are extremely slow on Linux. Everything else behaves normally, for example clicking anywhere in the overview bar or in the scrollbar is instantaneous. Navigating with the arrow keys (up/down, left/right) is also snappy.
Steps to reproduce
Open the browser and drag the rectangle in the overview bar. Or drag a scrollbar indicator.
Expected results
There shouldn't be any performance issues. I've tried this on macOS, and it works normally.
Actual results
On my Linux system (using Wayland), these operations are extremely slow, to the point that I get a popup dialog with "python3 is not responding".
Additional information
Installing pyopengl has no effect.
Platform Linux-6.15.9-arch1-1-x86_64-with-glibc2.42
Python 3.13.3 (main, Apr 9 2025, 04:03:52) [Clang 20.1.0 ]
Executable /home/clemens/Projects/mne-qt-browser/.venv/bin/python
CPU AMD Ryzen 7 5800X 8-Core Processor (16 cores)
Memory 15.5 GiB
Core
├☑ mne 1.10.0 (latest release)
├☑ numpy 2.3.2 (unknown linalg bindings (threadpoolctl module not found: No module named 'threadpoolctl'))
├☑ scipy 1.16.1
└☑ matplotlib 3.10.5 (backend=qtagg)
Numerical (optional)
└☐ unavailable sklearn, numba, nibabel, nilearn, dipy, openmeeg, cupy, pandas, h5io, h5py
Visualization (optional)
Fontconfig warning: using without calling FcInit()
├☑ qtpy 2.4.3 (PySide6=6.9.0)
├☑ pyqtgraph 0.13.7
├☑ mne-qt-browser 0.8.0.dev32+g62c9fe1
└☐ unavailable pyvista, pyvistaqt, vtk, ipympl, ipywidgets, trame_client, trame_server, trame_vtk, trame_vuetify
Ecosystem (optional)
└☐ unavailable mne-bids, mne-nirs, mne-features, mne-connectivity, mne-icalabel, mne-bids-pipeline, neo, eeglabio, edfio, mffpy, pybv
I would have expected the problem to be lack of pyopengl. After you installed it, do you see the message "using pyopengl" in the terminal when the plot window launches? (i.e., are we certain that it's actually getting used?)
No, I don't see anything. Should there be a message?
Using qt as 2D backend.
Fontconfig warning: using without calling FcInit()
qt.core.qobject.connect: QObject::connect(QStyleHints, QStyleHints): unique connections require a pointer to member function of a QObject subclass
Free RAM could not be determined because "psutil" is not installed. Setting precompute to False.
No, I don't see anything. Should there be a message?
I see this:
In [3]: raw.plot()
Using qt as 2D backend.
Using pyopengl with version 3.1.9
Out[3]: <mne_qt_browser._pg_figure.MNEQtBrowser at 0x7d31026a0550>
Free RAM could not be determined because "psutil" is not installed. Setting precompute to False
this is probably why you weren't seeing z-score as an option for overview mode here: https://github.com/mne-tools/mne-qt-browser/pull/343#issuecomment-3135236296
No idea why I'm not seeing this, but I don't think pyopengl should be necessary in the first place. You only need it if you want to directly draw with OpenGL, but that's not the case for Qt. Can you try if it makes a difference if you uninstall it?
I have a very recent MESA graphics driver for my AMD GPU installed, so 2D/3D acceleration is definitely working.
Also, I'm using Wayland and not X11, maybe this makes a difference?
And yes, installing psutil enables the z-score option!
Update: Indeed, Wayland is the culprit (as usual I'm almost inclined to say). If I fall back to X11 via export QT_QPA_PLATFORM=xcb, everything works as expected. If you want to try Wayland, you can export QT_QPA_PLATFORM=wayland instead.