BUG: Fix bug with scale bar overplotting

doc/changes/devel/12721.bugfix.rst

@@ -0,0 +1,2 @@
+Fix bug with overplotting of butterfly labels in :func:`mne.viz.plot_raw` and related
+functions and methods, by `Eric Larson`_.

mne/commands/mne_browse_raw.py

@@ -136,6 +136,13 @@ def run():
         default=None,
         action="store_true",
     )
+    parser.add_option(
+        "--butterfly",
+        dest="butterfly",
+        help="Plot in butterfly mode",
+        default=False,
+        action="store_true",
+    )
     _add_verbose_flag(parser)
     options, args = parser.parse_args()
 
@@ -167,6 +174,7 @@ def run():
                 pass
     filterchpi = options.filterchpi
     verbose = options.verbose
+    butterfly = options.butterfly
 
     if raw_in is None:
         parser.print_help()
@@ -202,6 +210,7 @@ def run():
         lowpass=lowpass,
         filtorder=filtorder,
         clipping=clipping,
+        butterfly=butterfly,
         proj=not proj_off,
         verbose=verbose,
         show=True,

mne/viz/_mpl_figure.py

@@ -1778,9 +1778,17 @@ def _check_update_vscroll_clicked(self, event):
 
     def _show_scalebars(self):
         """Add channel scale bars."""
-        for offset, pick in zip(self.mne.trace_offsets, self.mne.picks):
+        for pi, pick in enumerate(self.mne.picks):
             this_name = self.mne.ch_names[pick]
             this_type = self.mne.ch_types[pick]
+            # TODO: Simplify this someday -- we have to duplicate the challenging
+            # logic of _draw_traces here
+            offset_ixs = (
+                self.mne.picks
+                if self.mne.butterfly and self.mne.ch_selections is None
+                else slice(None)
+            )
+            offset = self.mne.trace_offsets[offset_ixs][pi]
             if (
                 this_type not in self.mne.scalebars
                 and this_type != "stim"

mne/viz/tests/test_raw.py

@@ -6,13 +6,15 @@
 import itertools
 import os
 from copy import deepcopy
+from pathlib import Path
 
 import matplotlib.pyplot as plt
 import numpy as np
 import pytest
 from matplotlib import backend_bases
 from numpy.testing import assert_allclose, assert_array_equal
 
+import mne
 from mne import Annotations, create_info, pick_types
 from mne._fiff.pick import _DATA_CH_TYPES_ORDER_DEFAULT, _PICK_TYPES_DATA_DICT
 from mne.annotations import _sync_onset
@@ -29,6 +31,9 @@
 from mne.viz import plot_raw, plot_sensors
 from mne.viz.utils import _fake_click, _fake_keypress
 
+base_dir = Path(__file__).parents[2] / "io" / "tests" / "data"
+raw_fname = base_dir / "test_raw.fif"
+
 
 def _get_button_xy(buttons, idx):
     from mne.viz._mpl_figure import _OLD_BUTTONS
@@ -1214,3 +1219,35 @@ def test_plotting_memory_garbage_collection(raw, pg_backend):
 
     assert len(mne_qt_browser._browser_instances) == 0
     _assert_no_instances(MNEQtBrowser, "after closing")
+
+
+def test_plotting_scalebars(browser_backend, qtbot):
+    """Test that raw scalebars are not overplotted."""
+    ismpl = browser_backend.name == "matplotlib"
+    raw = mne.io.read_raw_fif(raw_fname).crop(0, 1).load_data()
+    fig = raw.plot(butterfly=True)
+    if ismpl:
+        ch_types = [text.get_text() for text in fig.mne.ax_main.get_yticklabels()]
+        assert ch_types == ["mag", "grad", "eeg", "eog", "stim"]
+        delta = 0.25
+        offset = 0
+    else:
+        qtbot.wait_exposed(fig)
+        for _ in range(10):
+            ch_types = list(fig.mne.channel_axis.ch_texts)  # keys
+            if len(ch_types) > 0:
+                break
+            qtbot.wait(100)  # pragma: no cover
+        # the grad/mag difference here is intentional in _pg_figure.py
+        assert ch_types == ["grad", "mag", "eeg", "eog", "stim"]
+        delta = 0.5  # TODO: Probably should also be 0.25?
+        offset = 1
+    assert ch_types.pop(-1) == "stim"
+    for ci, ch_type in enumerate(ch_types, offset):
+        err_msg = f"{ch_type=} should be centered around y={ci}"
+        this_bar = fig.mne.scalebars[ch_type]
+        if ismpl:
+            yvals = this_bar.get_data()[1]
+        else:
+            yvals = this_bar.get_ydata()
+        assert_allclose(yvals, [ci - delta, ci + delta], err_msg=err_msg)