FIX: correct label orientation for 0-90 deg nodes in plot_connectivity_circle (#13855)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Daniel McCloy <dan@mccloy.info>

Author: 3 people

doc/changes/dev/13855.bugfix.rst

@@ -0,0 +1,3 @@
+Fixed incorrect label orientation for nodes in the 0–90° polar range (the
+12–3 o'clock quadrant) of the connectivity circle plot, by
+:newcontrib:`Pavel Popov`.

doc/changes/names.inc

@@ -258,6 +258,7 @@
 .. _Paul Pasler: https://github.com/ppasler
 .. _Paul Roujansky: https://github.com/paulroujansky
 .. _Pavel Navratil: https://github.com/navrpa13
+.. _Pavel Popov: https://github.com/paavalipopov
 .. _Peter Molfese: https://github.com/pmolfese
 .. _Phillip Alday: https://palday.bitbucket.io
 .. _Pierre Ablin: https://pierreablin.com

mne/viz/circle.py

@@ -338,7 +338,9 @@ def _plot_connectivity_circle(
     # Draw node labels
     angles_deg = 180 * node_angles / np.pi
     for name, angle_rad, angle_deg in zip(node_names, node_angles, angles_deg):
-        if angle_deg >= 270:
+        if (
+            angle_deg >= 270 or angle_deg < 90
+        ):  # [0, 90] and [270, 360] cover right half
             ha = "left"
         else:
             # Flip the label, so text is always upright

mne/viz/tests/test_circle.py

@@ -4,9 +4,11 @@
 
 
 import matplotlib
+import numpy as np
 import pytest
 
 from mne.viz import plot_channel_labels_circle
+from mne.viz.circle import _plot_connectivity_circle
 
 
 @pytest.mark.filterwarnings(
@@ -33,3 +35,50 @@ def test_plot_channel_labels_circle():
         plot_channel_labels_circle(
             dict(brain=["big", "great", "smart"]), colors=dict(big="r", great="y")
         )
+
+
+def test_plot_connectivity_circle_label_orientation():
+    """Labels in the 0-90 deg polar range (12-3 o'clock) must not be flipped.
+
+    Regression test: previously the condition ``angle_deg >= 270`` missed the
+    [0, 90) range, incorrectly adding 180 degrees to those labels and setting
+    ha='right', which caused them to point inward instead of outward.
+    """
+    # 9 nodes → uniform angles: 0, 40, 80, 120, 160, 200, 240, 280, 320 degrees.
+    # This guarantees coverage of all four quadrants, including the previously
+    # broken 0–90 range (nodes n0 at 0°, n1 at 40°, and n2 at 80°).
+    n_nodes = 9
+    con = np.ones((n_nodes, n_nodes))
+    con[::2, ::2] = 0  # add some zeros to avoid 0-div in normalization
+    node_names = [f"n{i}" for i in range(n_nodes)]
+
+    fig, ax = _plot_connectivity_circle(con, node_names, show=False)
+
+    texts = [c for c in ax.get_children() if isinstance(c, matplotlib.text.Text)]
+    label_texts = {t.get_text(): t for t in texts if t.get_text() in node_names}
+
+    # node_angles defaults to np.linspace(0, 2*pi, n_nodes, endpoint=False)
+    angles_deg = np.linspace(0, 360, n_nodes, endpoint=False)
+
+    assert len(label_texts) == n_nodes, (
+        f"Expected {n_nodes} label texts, found {len(label_texts)}"
+    )
+
+    for angle, name in zip(angles_deg, node_names, strict=True):
+        t = label_texts[name]
+        ha = t.get_ha()
+
+        if angle >= 270 or angle < 90:
+            # Right half of circle: text must extend outward to the right.
+            # ha='left' anchors the left edge at the node, text goes rightward.
+            assert ha == "left", (
+                f"Node '{name}' at {angle:.1f}° (right half) should have "
+                f"ha='left', got '{ha}'"
+            )
+        else:
+            # Left half: text is flipped 180° so it stays upright; ha='right'
+            # anchors the right edge at the node, text extends leftward/outward.
+            assert ha == "right", (
+                f"Node '{name}' at {angle:.1f}° (left half) should have "
+                f"ha='right', got '{ha}'"
+            )