WIP, ENH: Automatic theme switching on macOS

mne/viz/backends/_qt.py

@@ -11,7 +11,7 @@
 import pyvista
 from pyvistaqt.plotting import FileDialog, MainWindow
 
-from qtpy.QtCore import Qt, Signal, QLocale, QObject
+from qtpy.QtCore import Qt, Signal, QLocale, QObject, QEvent
 from qtpy.QtGui import QIcon, QCursor
 from qtpy.QtWidgets import (QComboBox, QDockWidget, QDoubleSpinBox, QGroupBox,
                             QHBoxLayout, QLabel, QToolButton, QMenuBar,
@@ -723,12 +723,7 @@ def _window_set_theme(self, theme=None):
         else:
             default_theme = theme
         theme = get_config('MNE_3D_OPTION_THEME', default_theme)
-        stylesheet = _qt_get_stylesheet(theme)
-        self._window.setStyleSheet(stylesheet)
-        if _qt_is_dark(self._window):
-            QIcon.setThemeName('dark')
-        else:
-            QIcon.setThemeName('light')
+        _set_window_theme(self._window, theme)
 
 
 class _QtWidgetList(_AbstractWidgetList):
@@ -921,6 +916,21 @@ def _create_dock_widget(window, name, area, *, max_width=None):
     return dock, dock_layout
 
 
+def _set_window_theme(window, theme):
+    stylesheet = _qt_get_stylesheet(theme)
+    # The setStyleSheet() function triggers a PaletteChange event so we
+    # need to filter out the newly created one to avoid ending in an
+    # infinite loop.
+    event_filter = _DiscardEventFilter('PaletteChange')
+    window.installEventFilter(event_filter)
+    window.setStyleSheet(stylesheet)
+    window.removeEventFilter(event_filter)
+    if _qt_is_dark(window):
+        QIcon.setThemeName('dark')
+    else:
+        QIcon.setThemeName('light')
+
+
 @contextmanager
 def _testing_context(interactive):
     from . import renderer
@@ -942,6 +952,19 @@ def _testing_context(interactive):
         renderer.MNE_3D_BACKEND_INTERACTIVE = orig_interactive
 
 
+class _DiscardEventFilter(QObject):
+    def __init__(self, event_name):
+        super().__init__()
+        self._event_type = getattr(QEvent, event_name)
+
+    def eventFilter(self, obj, ev):
+        if ev.type() == self._event_type:
+            ev.accept()
+            return True
+        else:
+            return False
+
+
 # In theory we should be able to do this later (e.g., in _pyvista.py when
 # initializing), but at least on Qt6 this has to be done earlier. So let's do
 # it immediately upon instantiation of the QMainWindow class.
@@ -952,3 +975,10 @@ class _MNEMainWindow(MainWindow):
     def __init__(self, parent=None, title=None, size=None):
         super().__init__(parent, title, size)
         self.setAttribute(Qt.WA_ShowWithoutActivating, True)
+
+    def event(self, ev):
+        """Catch system events."""
+        if ev.type() == QEvent.PaletteChange:  # detect theme switches
+            theme = get_config('MNE_3D_OPTION_THEME', 'auto')
+            _set_window_theme(self, theme)
+        return super().event(ev)