Add support for mouse wheel scrolling in raw.plot() (mne-tools#13988)

Co-authored-by: Eric Larson <larson.eric.d@gmail.com>

Author: cbrnr

doc/changes/dev/13988.newfeature.rst

@@ -0,0 +1 @@
+Add mouse wheel scrolling support to the ``'matplotlib'`` browser backend to navigate through channels, by `Clemens Brunner`_.

mne/viz/_mpl_figure.py

@@ -220,6 +220,10 @@ def _buttonpress(self, event):
         """Handle buttonpress events."""
         pass
 
+    def _scroll(self, event):
+        """Handle scroll wheel events."""
+        pass
+
     def _pick(self, event):
         """Handle matplotlib pick events."""
         pass
@@ -241,6 +245,7 @@ def _add_default_callbacks(self, **kwargs):
             resize_event=self._resize,
             key_press_event=self._keypress,
             button_press_event=self._buttonpress,
+            scroll_event=self._scroll,
             close_event=self._close,
             pick_event=self._pick,
         )
@@ -958,6 +963,20 @@ def _buttonpress(self, event):
             elif event.inaxes == ax_main:
                 self._toggle_vline(False)
 
+    def _scroll(self, event):
+        """Handle scroll wheel events for channel navigation."""
+        if self.mne.butterfly or self.mne.fig_selection is not None:
+            return
+        direction = -1 if event.button == "up" else 1
+        ceiling = len(self.mne.ch_order) - self.mne.n_channels
+        old_start = self.mne.ch_start
+        self.mne.ch_start = np.clip(self.mne.ch_start + direction, 0, ceiling)
+        if self.mne.ch_start == old_start:
+            return
+        self._update_picks()
+        self._update_vscroll()
+        self._redraw()
+
     def _pick(self, event):
         """Handle matplotlib pick events."""
         from matplotlib.text import Text
@@ -1111,6 +1130,7 @@ def _get_help_text(self):
                 ("?", "Open this help window"),
                 ("esc", "Close focused figure or dialog window"),
                 ("_MOUSE INTERACTION", " "),
+                ("Scroll wheel", "Scroll channels up/down"),
                 (f"Left-click {ch_cmp} name", lclick_name),
                 (f"Left-click {ch_cmp} data", lclick_data),
                 ("Left-click-and-drag on plot", ldrag),

mne/viz/tests/test_raw.py

@@ -589,6 +589,32 @@ def test_plot_raw_keypresses(raw, browser_backend):
         fig._fake_keypress(key)
 
 
+def test_plot_raw_scroll(raw, browser_backend):
+    """Test scroll wheel channel navigation in raw.plot()."""
+    with raw.info._unlock():
+        raw.info["lowpass"] = 10.0
+    # use n_channels < total so there is room to scroll
+    fig = raw.plot(n_channels=3)
+    assert len(fig.mne.ch_order) > fig.mne.n_channels  # sanity check
+    # the sign of "step" that means "scroll down" differs between backends
+    down, up = (-1, 1) if browser_backend.name == "matplotlib" else (1, -1)
+    # scroll down moves ch_start forward by 1
+    ch_start_before = fig.mne.ch_start
+    fig._fake_scroll(0.5, 0.5, down)
+    assert fig.mne.ch_start == ch_start_before + 1
+    # scroll up moves ch_start back by 1
+    fig._fake_scroll(0.5, 0.5, up)
+    assert fig.mne.ch_start == ch_start_before
+    # scroll up at the top is a no-op (already at 0)
+    assert fig.mne.ch_start == 0
+    fig._fake_scroll(0.5, 0.5, up)
+    assert fig.mne.ch_start == 0
+    # scroll is a no-op in butterfly mode
+    fig._fake_keypress("b")
+    fig._fake_scroll(0.5, 0.5, down)
+    assert fig.mne.ch_start == 0
+
+
 def test_plot_raw_traces(raw, events, browser_backend):
     """Test plotting of raw data."""
     ismpl = browser_backend.name == "matplotlib"