FIX: Handle hidden annotations during deletion in mpl plot (#13703)

Author: DerAndereJohannes

doc/changes/dev/13703.bugfix.rst

@@ -0,0 +1 @@
+Fix annotation removal logic in matplotlib based figures to correctly handle non-contiguous visible annotations, by `Johannes Herforth`_.

mne/viz/_mpl_figure.py

@@ -838,8 +838,7 @@ def _buttonpress(self, event):
                     # (ax_main.collections only includes *visible* annots, so we offset)
                     visible_zorders = [span.zorder for span in spans]
                     zorders = np.zeros_like(is_onscreen).astype(int)
-                    offset = np.where(is_onscreen)[0][0]
-                    zorders[offset : (offset + len(visible_zorders))] = visible_zorders
+                    zorders[is_onscreen] = visible_zorders
                     # among overlapping clicked spans, prefer removing spans whose label
                     # is the active label; then fall back to zorder as deciding factor
                     active_clicked = was_clicked & is_active_label

mne/viz/tests/test_raw.py

@@ -826,6 +826,24 @@ def test_plot_annotations(raw, browser_backend):
         not fig.mne.visible_annotations["test"] and fig.mne.visible_annotations["test2"]
     )
 
+    if ismpl:
+        # gh-13511: hide the middle annotation to get non-contiguous is_onscreen=[T,F,T]
+        annot = Annotations(
+            onset=[2, 2, 2], duration=[3, 3, 3], description=["A", "B", "C"]
+        )
+        raw.set_annotations(annot)
+        fig = raw.plot(start=0, duration=10)
+        fig._fake_keypress("a")
+        # hide "B" so is_onscreen = [T, F, T]
+        fig.mne.show_hide_annotation_checkboxes.set_active(1)
+        buttons = fig.mne.fig_annotation.mne.radio_ax.buttons
+        # set active to the hidden "B" so deletion falls back to zorder
+        buttons.set_active(1)
+        fig._fake_click((2.5, 1.0), xform="data", button=3)
+        # C has the highest zorder and should be deleted; the bug deleted A instead
+        assert "C" not in raw.annotations.description
+        assert "A" in raw.annotations.description
+
 
 @pytest.mark.parametrize("active_annot_idx", (0, 1, 2))
 def test_overlapping_annotation_deletion(raw, browser_backend, active_annot_idx):