Fix y-label overlap with tick labels for non-default rotations (#19029)

FazeelUsmani · FazeelUsmani · commit 7b376d5a1cf4 · 2026-04-07T15:54:39.000+05:30
`YAxis._update_label_position` previously assumed a 90° label rotation when computing the label's position, so y-labels with other rotations (e.g. ``rotation=270`` for right-side colorbar labels) could overlap the tick labels. The label position is now computed from the rendered label's actual extent, so it sits clear of the tick labels for any rotation. This implements @jklymak's suggestion in the issue thread of checking the rendered label extent against the tick labels in `_update_label_position`. The fix is a no-op for the default ``rotation=90`` case, so existing image baselines are unaffected. Tests added in test_axes.py cover the generic axis-layer fix (parametrized over 7 rotations × 2 label_positions) plus an ``align_ylabels`` regression that guards against the per-axis overhang correction breaking sibling alignment when rotations differ. A colorbar smoke test in test_colorbar.py exercises the original user-facing symptom from the issue via ``cbar.set_label(..., rotation=270)``.
diff --git a/doc/api/next_api_changes/behavior/19029-FU.rst b/doc/api/next_api_changes/behavior/19029-FU.rst
@@ -0,0 +1,11 @@
+y-axis labels with non-default rotation no longer overlap tick labels
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Setting a y-axis label with a rotation other than the default (e.g.
+``ax.set_ylabel("...", rotation=270)``, or ``cbar.set_label("...",
+rotation=270)`` on a colorbar) previously could cause the label to
+overlap the tick labels because the automatic label placement assumed a
+90° rotation. The label position is now computed from the rendered
+label's actual extent, so it sits clear of the tick labels for any
+rotation. This may shift the position of y-labels that use non-default
+rotations.
diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
@@ -2735,14 +2735,27 @@ def _update_label_position(self, renderer):
             # Union with extents of the left spine if present, of the axes otherwise.
             bbox = mtransforms.Bbox.union([
                 *bboxes, self.axes.spines.get("left", self.axes).get_window_extent()])
-            self.label.set_position(
-                (bbox.x0 - self.labelpad * self.get_figure(root=True).dpi / 72, y))
+            target_x = bbox.x0 - self.labelpad * self.get_figure(root=True).dpi / 72
+            self.label.set_position((target_x, y))
+            # The vertical alignment set in `set_label_position` assumes a
+            # 90° rotation; for any other rotation the rotated label may
+            # extend back toward the tick labels and overlap them. Shift
+            # the label outward by the overhang. See issue #19029.
+            label_bbox = self.label.get_window_extent(renderer)
+            overhang = label_bbox.x1 - target_x
+            if overhang > 0:
+                self.label.set_position((target_x - overhang, y))
         else:
             # Union with extents of the right spine if present, of the axes otherwise.
             bbox = mtransforms.Bbox.union([
                 *bboxes2, self.axes.spines.get("right", self.axes).get_window_extent()])
-            self.label.set_position(
-                (bbox.x1 + self.labelpad * self.get_figure(root=True).dpi / 72, y))
+            target_x = bbox.x1 + self.labelpad * self.get_figure(root=True).dpi / 72
+            self.label.set_position((target_x, y))
+            # See comment in the 'left' branch above (issue #19029).
+            label_bbox = self.label.get_window_extent(renderer)
+            overhang = target_x - label_bbox.x0
+            if overhang > 0:
+                self.label.set_position((target_x + overhang, y))
 
     def _update_offset_text_position(self, bboxes, bboxes2):
         """
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -9070,6 +9070,54 @@ def test_ylabel_ha_with_position(ha):
     assert ax.yaxis.label.get_ha() == ha
 
 
+@pytest.mark.parametrize('label_position', ['left', 'right'])
+@pytest.mark.parametrize('rotation', [0, 45, 90, 135, 180, 270, -90])
+def test_ylabel_no_overlap_with_ticklabels(label_position, rotation):
+    """Regression test for #19029: a y-label with rotation other than 90°
+    must not overlap the tick labels regardless of label_position."""
+    fig, ax = plt.subplots()
+    ax.plot([1, 3, 2])
+    ax.yaxis.set_label_position(label_position)
+    if label_position == 'right':
+        ax.yaxis.tick_right()
+    ax.set_ylabel("test label", rotation=rotation)
+    fig.canvas.draw()
+    renderer = fig.canvas.get_renderer()
+    label_bbox = ax.yaxis.label.get_window_extent(renderer)
+    tick_bboxes = [t.get_window_extent(renderer)
+                   for t in ax.yaxis.get_ticklabels() if t.get_visible()]
+    tick_union = mtransforms.Bbox.union(tick_bboxes)
+    if label_position == 'right':
+        assert label_bbox.x0 >= tick_union.x1
+    else:
+        assert label_bbox.x1 <= tick_union.x0
+
+
+@pytest.mark.parametrize('label_position', ['left', 'right'])
+def test_align_ylabels_mixed_rotation(label_position):
+    """Issue #19029: ``fig.align_ylabels`` must keep two y-labels visually
+    aligned even when they use different rotations. The per-axis overhang
+    correction in `_update_label_position` shifts each axis independently;
+    this test guards against that breaking sibling alignment."""
+    fig, axs = plt.subplots(2, figsize=(4, 6))
+    for ax in axs:
+        ax.plot([1, 30, 2])
+        ax.yaxis.set_label_position(label_position)
+        if label_position == 'right':
+            ax.yaxis.tick_right()
+    axs[0].set_ylabel('first', rotation=90)
+    axs[1].set_ylabel('second', rotation=270)
+    fig.align_ylabels(axs)
+    fig.canvas.draw()
+    renderer = fig.canvas.get_renderer()
+    bbox0 = axs[0].yaxis.label.get_window_extent(renderer)
+    bbox1 = axs[1].yaxis.label.get_window_extent(renderer)
+    # Both visible label bboxes should occupy the same horizontal range,
+    # even though the underlying anchor positions differ between rotations.
+    assert bbox0.x0 == pytest.approx(bbox1.x0, abs=0.5)
+    assert bbox0.x1 == pytest.approx(bbox1.x1, abs=0.5)
+
+
 def test_bar_label_location_vertical():
     ax = plt.gca()
     xs, heights = [1, 2], [3, -4]
diff --git a/lib/matplotlib/tests/test_colorbar.py b/lib/matplotlib/tests/test_colorbar.py
@@ -733,6 +733,24 @@ def test_colorbar_label():
     assert cbar3.ax.get_xlabel() == 'horizontal cbar'
 
 
+def test_colorbar_label_rotation_no_overlap():
+    """Smoke test for #19029: a rotation=270 colorbar label must not
+    overlap negative tick labels (the original user-facing symptom)."""
+    fig, ax = plt.subplots()
+    im = ax.imshow([[-100, 0], [50, 100]])
+    cbar = fig.colorbar(im, ax=ax)
+    cbar.set_label('RT(1ax) - RT(2ax) [ms]', rotation=270)
+    fig.canvas.draw()
+    renderer = fig.canvas.get_renderer()
+    label_bbox = cbar.ax.yaxis.label.get_window_extent(renderer)
+    # Colorbar labels live on the right, so the label must sit clear of
+    # the rightmost visible tick-label edge.
+    tick_x1_max = max(t.get_window_extent(renderer).x1
+                      for t in cbar.ax.yaxis.get_ticklabels()
+                      if t.get_visible())
+    assert label_bbox.x0 >= tick_x1_max
+
+
 # TODO: tighten tolerance after baseline image is regenerated for text overhaul
 @image_comparison(['colorbar_keeping_xlabel.png'], style='mpl20', tol=0.03)
 def test_keeping_xlabel():
