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ENH: add a vtk.js backend for MNE's 3D renderer (JupyterLite split 3/5) - #14144

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larsoner merged 35 commits into
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natinew77-creator:lite-browser-runtime
Sep 3, 2026
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ENH: add a vtk.js backend for MNE's 3D renderer (JupyterLite split 3/5)#14144
larsoner merged 35 commits into
mne-tools:mainfrom
natinew77-creator:lite-browser-runtime

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@natinew77-creator natinew77-creator commented Aug 8, 2026

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Part 3 of the split of #13925. Parts 1 and 2 are #14128 and #14135.

Adds a drawing backend for MNE's 3D renderer that uses vtk.js, since VTK itself cannot load in WebAssembly. MNE's 3D functions do their geometry and coordinate-frame work in numpy and only hand the result to a renderer, so replacing that last step leaves the transform maths with MNE. That matters here, because a subtly wrong head or device transform still produces a plausible-looking picture.

Supported: meshes, surfaces, spheres, tubes and glyphs, which covers the static figures the docs render. Not supported: the interactive Brain time viewer, which needs dock widgets, and scalar colormaps, which pyvista-js 0.15 does not have.

It is a plain string constant, so nothing in the build touches it yet. The setup cell that appends it is #14150.

VTK cannot load in WebAssembly, so the JupyterLite notebooks need a renderer
that draws with vtk.js. MNE does its geometry in numpy and only hands the result
to a renderer, so replacing that last step leaves the transform maths to MNE.
@natinew77-creator natinew77-creator changed the title ENH: add the JupyterLite browser runtime (JupyterLite split 3/4) ENH: add a vtk.js backend for MNE's 3D renderer (JupyterLite split 3/5) Aug 11, 2026
@larsoner

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Maybe you have looked and I am coming late to this... have you thought about adding it as a type of AbstractRenderer and using https://github.com/tkoyama010/pyvista-js ? Maybe it's not too much work to use that in place of our PyVista calls... but if you've tried or looked I could be way off!

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Maybe you have looked and I am coming late to this... have you thought about adding it as a type of AbstractRenderer and using https://github.com/tkoyama010/pyvista-js ? Maybe it's not too much work to use that in place of our PyVista calls... but if you've tried or looked I could be way off!

Hi Eric, it already uses pyvista-js.

On AbstractRenderer, it sits in doc/ as a string the setup cell appends, to keep browser-only code out of mne/. But it already implements 21 of the 22 abstract methods, so converting it is mostly moving and registering it, not a rewrite.

Happy to do that here, or land this as is and convert in a follow-up. Which would you prefer?

Thanks!

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Yeah if there is some way for it to be a plain renderer and then LITE_RENDERER_CELL can be built from the source rather than being a huge string that would be better. The huge string doesn't have Python linting etc. built in which is a real drawback. It would also maybe facilitate eventually adding selenium-based unit tests for the renderer or something. But maybe @teonbrooks has ideas!

natinew77-creator and others added 2 commits August 17, 2026 16:52
The renderer was a 560-line string literal, which no linter or formatter
could see. It now lives in _lite_renderer_cell.py as ordinary Python and
the cell is read from there, so ruff covers it like any other file. The
code itself is unchanged apart from what the formatter did to it.
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Yeah if there is some way for it to be a plain renderer and then LITE_RENDERER_CELL can be built from the source rather than being a huge string that would be better. The huge string doesn't have Python linting etc. built in which is a real drawback. It would also maybe facilitate eventually adding selenium-based unit tests for the renderer or something. But maybe @teonbrooks has ideas!

Done in eb3c814, it's a plain module now and LITE_RENDERER_CELL is read from it, so ruff and the formatter cover it.

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I think it's probably best to move this to the mne/viz/backends/_<something>.py and test it. The testing will be a bit tricky... could we use a Jupyter notebook-style test like we have already? If it requires a proper browser, maybe selenium or something... @drammock could maybe advise based on what pydata-sphinx-theme has.

I don't want to add 700 lines with no unit tests, things are bound to break / or be broken...

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I think it's probably best to move this to the mne/viz/backends/_<something>.py and test it. The testing will be a bit tricky... could we use a Jupyter notebook-style test like we have already? If it requires a proper browser, maybe selenium or something... @drammock could maybe advise based on what pydata-sphinx-theme has.

I don't want to add 700 lines with no unit tests, things are bound to break / or be broken...

Done, moved to mne/viz/backends/_lite.py as a real _AbstractRenderer subclass. That turned up a bug, it reported a _kind that isn't "notebook", sending _coreg.py into _qt_app_exec with no Qt event loop in a browser.

pyvista-js is pure Python, so no selenium, 18 pytest cases plus one nbexec test. It ships in the wheel now too, so the setup cell drops from ~24,500 characters to 438.

I didn't register it in VALID_3D_BACKENDS, since that pulls in the 17 widget classes _do_widget_tests expects. Happy to if you meant that.

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Thanks for the quick response @natinew77-creator. I only have phone at the moment but will look again tomorrow morning

Matches what the review asked for and lines the backend name up with _kind.
The capability table goes back to upstream's three columns, with the browser
backend described in the notes instead.
Comment thread mne/viz/backends/_lite.py Outdated
Comment thread mne/viz/backends/_lite.py Outdated
Comment thread mne/viz/backends/_lite.py Outdated
Comment thread mne/viz/backends/tests/test_lite.py Outdated
Comment thread mne/viz/backends/tests/test_lite.py Outdated
It was handing back only the last color group and dropping the rest.
Drops a wrong claim about plot_bem, makes the drawing tests assert geometry
rather than actor counts, and stops accepting arguments without saying why
they cannot be honoured.
mne-toolsgh-13074 made mne/viz/_3d.py write channel names onto the second value
instanced_mesh returns, which broke plot_alignment here three ways: a
pyvista-js PolyData has no field_data, several colours came back as a
list, and empty positions came back as None. Return the per-instance
point cloud instead, always one object with the mapping attached, which
is what _PyVistaRenderer returns.
@larsoner
larsoner requested a review from wmvanvliet as a code owner September 3, 2026 17:19
* upstream/main: (37 commits)
  Speed up evoked time plotting (mne-tools#14249)
  Persist the numba JIT cache, sysmon coverage, refleak freeze (mne-tools#14265)
  Fix interpolate_to spline target positions (mne-tools#14266)
  CI reduce package builds on pull requests (mne-tools#14264)
  Avoid copying all epochs data in GetEpochsMixin._getitem (mne-tools#14262)
  Add Report.save(only_if_changed=True) (mne-tools#14261)
  Add jamica to related software [ci skip] (mne-tools#14260)
  Remove debugging cruft (mne-tools#14259)
  ENH: add Raw annotation span conversion (mne-tools#14240)
  Interactive dipole fitting: add STC mesh controls (mne-tools#14256)
  Document code principles in AGENTS.md (mne-tools#14239)
  MAINT: Update dependency specifiers (mne-tools#14257)
  [dependabot]: Bump the actions group with 2 updates (mne-tools#14258)
  ENH: Add JAMICA as an ICA method (mne-tools#14247)
  Reuse the MEF session across reads (mne-tools#14254)
  Read KIT data in cache-sized blocks (mne-tools#14255)
  Read EGI simple-binary event channels in blocks (mne-tools#14250)
  Decode Persyst and Nihon Kohden data in cache-sized blocks (mne-tools#14251)
  Normalize byte order before calibrating strided integer buffers (mne-tools#14252)
  Speed up EDF and BDF reading (mne-tools#14237)
  ...
@larsoner

larsoner commented Sep 3, 2026

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Okay I added it as a proper renderer in tests in d6b8de46e1e16287a7eed50a9cb2ed209e1d62ec5257722a2c0fce32dd2c726aR740 , which exposed a number of issues that are now fixed. Marking for merge-when-green, thanks in advance @natinew77-creator !

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larsoner enabled auto-merge (squash) September 3, 2026 17:21
@larsoner
larsoner dismissed drammock’s stale review September 3, 2026 17:21

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larsoner disabled auto-merge September 3, 2026 17:32
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@natinew77-creator

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Okay I added it as a proper renderer in tests in d6b8de46e1e16287a7eed50a9cb2ed209e1d62ec5257722a2c0fce32dd2c726aR740 , which exposed a number of issues that are now fixed. Marking for merge-when-green, thanks in advance @natinew77-creator !

Thanks Eric, this turned out much better than what I had. I appreciate you taking the time to convert it into a proper renderer and to fix the rotation edge case along the way.

@larsoner

larsoner commented Sep 3, 2026

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Working on fixing the Windows timeout... I don't think it's related so I'm going to do it in another branch, then merge main into this one.

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Working on fixing the Windows timeout... I don't think it's related so I'm going to do it in another branch, then merge main into this one.

Sounds good, thanks.

@larsoner

larsoner commented Sep 3, 2026

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It's just scipy's intersphinx inventory which has been having trouble all day

@larsoner
larsoner merged commit ba76974 into mne-tools:main Sep 3, 2026
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4 participants