Try removing all the _process_events calls and see what happens

.gitignore

@@ -103,4 +103,5 @@ venv/
 .hypothesis/
 .ruff_cache/
 .ipynb_checkpoints/
-/.claude/
+/.claude/
+uv.lock

mne/viz/_brain/_brain.py

@@ -631,7 +631,6 @@ def setup_time_viewer(self, time_viewer=True, show_traces=True):
         for hemi in ("lh", "rh"):
             for ri, ci, v in self._iter_views(hemi):
                 self.show_view(view=v, row=ri, col=ci)
-        self._renderer._process_events()
 
         self._renderer._update()
         # finally, show the MplCanvas
@@ -1028,7 +1027,7 @@ def _refresh_colormap_widgets(self):
             fmid=self._data["fmid"],
             fmax=self._data["fmax"],
         )
-        self._renderer._process_events()
+        self._renderer._update()
 
     def _configure_dock_trace_widget(self, name):
         if not self.show_traces:
@@ -1520,7 +1519,7 @@ def _on_time_change(self, event):
                 if "current_time" in self.widgets:
                     self.widgets["current_time"].set_value(f"{self._current_time: .3f}")
             self.plot_time_line(update=True)
-        self._renderer._process_events()
+        self._renderer._update()
 
     def _on_colormap_range(self, event):
         """Respond to the colormap_range UI event."""
@@ -1541,7 +1540,7 @@ def _on_colormap_range(self, event):
                         self.widgets[entry_key].set_value(val * self._data["fscale"])
         # Update the render.
         self._update_colormap_range(**lims)
-        self._renderer._process_events()
+        self._renderer._update()
 
     def _on_vertex_select(self, event):
         """Respond to vertex_select UI event."""
@@ -3683,7 +3682,6 @@ def show_view(
                     self._set_camera(**view_params, align=align)
         if update:
             self._renderer._update()
-            self._renderer._process_events()
 
     def _set_camera(
         self,

mne/viz/_brain/tests/test_brain.py

@@ -916,7 +916,9 @@ def test_image_screenshot(
     """Test screenshot and image saving."""
     size = (300, 300)
     brain = _create_testing_brain(hemi="rh", show_traces=False, size=size)
-    azimuth, elevation = 180.0, 90.0
+    for mesh in brain.layered_meshes.values():
+        mesh._actor.SetVisibility(True)
+    azimuth, elevation = 360.0, 90.0
     fname = tmp_path / "test.png"
     assert not fname.is_file()
     brain.save_image(fname)
@@ -938,6 +940,17 @@ def test_image_screenshot(
     div = 2 if np.allclose(img.shape[:2], want_size[:2] / 2.0, atol=15) else 1
     want_size[:2] /= div
     assert_allclose(img.shape, want_size, atol=15)
+
+    # Test whether the renderer has properly updated before the screenshot was taken.
+    brain.set_time(1)
+    img1 = brain.screenshot(mode="rgba")
+    brain.set_time(2)
+    img2 = brain.screenshot(mode="rgba")
+    brain.set_time(1)
+    img3 = brain.screenshot(mode="rgba")
+    assert not np.array_equal(img1, img2)
+    assert_array_equal(img1, img3)
+
     brain.close()
 
 

mne/viz/backends/_pyvista.py

@@ -18,7 +18,12 @@
 
 import numpy as np
 import pyvista
-from pyvista import Line, Plotter, PolyData, close_all  # noqa: F401  # re-exported
+from pyvista import (
+    Line,
+    Plotter,  # noqa: F401  # re-exported
+    PolyData,  # noqa: F401  # re-exported
+    close_all,
+)
 from pyvista.plotting.plotter import _ALL_PLOTTERS
 from pyvistaqt import BackgroundPlotter
 from vtkmodules.util.numpy_support import numpy_to_vtk
@@ -50,12 +55,7 @@
 from ...fixes import _compare_version
 from ...surface import _vtk_smooth
 from ...transforms import _cart_to_sph, _sph_to_cart, apply_trans
-from ...utils import (
-    _check_option,
-    _require_version,
-    _validate_type,
-    warn,
-)
+from ...utils import _check_option, _require_version, _validate_type, warn
 from ._abstract import Figure3D, _AbstractRenderer
 from ._utils import (
     ALLOWED_QUIVER_MODES,
@@ -156,7 +156,6 @@ def _build(self):
         if self.plotter.iren is not None:
             self.plotter.iren.initialize()
         _process_events(self.plotter)
-        _process_events(self.plotter)
         return self.plotter
 
     def _is_active(self):
@@ -289,14 +288,10 @@ def _hide_axes(self):
     def _update(self):
         for plotter in self._all_plotters:
             # PyVistaQt resolves plotter.update() to QWidget.update(), which only
-            # schedules a repaint, and it makes Plotter.render() asynchronous (the
-            # synchronous one being _render()). So render synchronously to update the
-            # scene, schedule the repaint, then flush it: without the flush the paint
-            # is delivered whenever events happen to be processed next, which can be
-            # long after the scene has changed again.
-            getattr(plotter, "_render", plotter.render)()
-            plotter.update()
-            _process_events(plotter)
+            # schedules a repaint, and it makes Plotter.render() asynchronous. This is
+            # probably fine for most cases. If you want to synchronously, i.e. wait
+            # until it has actually gone through, use Plotter._render().
+            plotter.render()
 
     def _index_to_loc(self, idx):
         _ncols = self.figure._ncols
@@ -990,9 +985,9 @@ def _actor(self, mapper=None):
         _hide_testing_actor(actor)
         return actor
 
-    def _process_events(self):
+    def _process_events(self, level=0):
         for plotter in self._all_plotters:
-            _process_events(plotter)
+            _process_events(plotter, level=level + 1)
 
     def _update_picking_callback(
         self, on_mouse_move, on_button_press, on_button_release, on_pick
@@ -1394,7 +1389,6 @@ def _set_3d_view(
 
     if update:
         figure.plotter.update()
-        _process_events(figure.plotter)
 
 
 def _set_3d_title(figure, title, size=16, *, color="white", position="upper_left"):
@@ -1406,7 +1400,6 @@ def _set_3d_title(figure, title, size=16, *, color="white", position="upper_left
         name="title",
     )
     figure.plotter.update()
-    _process_events(figure.plotter)
     return handle
 
 
@@ -1416,7 +1409,7 @@ def _check_3d_figure(figure):
 
 def _clear_3d_figure(figure):
     figure.plotter.clear()  # remove all actors, lights are restored on the next plot
-    _process_events(figure.plotter)
+    figure.plotter.update()
 
 
 def _close_3d_figure(figure):
@@ -1428,17 +1421,19 @@ def _close_3d_figure(figure):
     # free memory and deregister from the scraper
     plotter.deep_clean()  # remove internal references
     _ALL_PLOTTERS.pop(plotter._id_name, None)
-    _process_events(plotter)
 
 
 def _take_3d_screenshot(figure, mode="rgb", filename=None):
-    _process_events(figure.plotter)
+    # force the render to happen right now if it's an option (not available on
+    # notebooks)
+    meth = getattr(figure.plotter, "_render", figure.plotter.render)
+    meth()
     return figure.plotter.screenshot(
         transparent_background=(mode == "rgba"), filename=filename
     )
 
 
-def _process_events(plotter):
+def _process_events(plotter, level=0):
     if hasattr(plotter, "app"):
         with warnings.catch_warnings(record=True):
             warnings.filterwarnings("ignore", "constrained_layout")

mne/viz/evoked_field.py

@@ -229,7 +229,7 @@ def current_time_func():
                     current_time_func=current_time_func,
                     times=evoked.times,
                 )
-            if not self._in_brain_figure or "time_slider" not in fig.widgets:
+
                 # Draw the time label
                 self._time_label = time_label
                 if time_label is not None:
@@ -373,7 +373,7 @@ def _update(self):
                 x_window=0.01, y_window=0.01, text=time_label
             )
 
-        self._renderer.plotter.update()
+        self._renderer._update()
 
     def _configure_dock(self):
         """Configure the widgets shown in the dock on the left."""
@@ -383,7 +383,7 @@ def _configure_dock(self):
             r._dock_initialize()
 
         # Fieldline configuration
-        layout = r._dock_add_group_box("Fieldlines")
+        layout = r._dock_add_group_box("Fieldlines", collapse=True)
 
         r._dock_add_label(value="max value", align=True, layout=layout)
 

tools/vulture_allowlist.py

@@ -40,6 +40,7 @@
 _use_test_3d_backend
 verbose_debug
 metadata_routing
+Plotter
 
 # Decoding
 _.multi_class