FIX: Autoposition title when yaxis has offset

Move any title above the y axis offset text it would overlap with the
offset. If multiple titles are present, they are vertically aligned to
the highest one.

Author: StefRe

doc/api/next_api_changes/behavior/22063-SR.rst

@@ -0,0 +1,7 @@
+Move Axes title to not overlap with y axis offset
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Previously, Axes titles could overlap the y-axis offset text, which is often
+in the upper left corner of the axes.  Now titles are moved above the offset
+text if overlapping, and autopositioning is in effect (i.e. if *y* in
+`.Axes.set_title` is *None* and :rc:`axes.titley` is also *None*).

lib/matplotlib/axes/_base.py

@@ -2990,6 +2990,12 @@ def _update_title_position(self, renderer):
                 if bb is None:
                     bb = ax.get_window_extent(renderer)
                 top = max(top, bb.ymax)
+                if title.get_text():
+                    ax.yaxis.get_tightbbox(renderer)  # update offsetText
+                    if ax.yaxis.offsetText.get_text():
+                        bb = ax.yaxis.offsetText.get_tightbbox(renderer)
+                        if bb.intersection(title.get_tightbbox(renderer), bb):
+                            top = bb.ymax
             if top < 0:
                 # the top of Axes is not even on the figure, so don't try and
                 # automatically place it.

lib/matplotlib/tests/test_axes.py

@@ -6121,6 +6121,36 @@ def test_title_xticks_top_both():
     assert ax.title.get_position()[1] > 1.04
 
 
+@pytest.mark.parametrize(
+    'left, center', [
+        ('left', ''),
+        ('', 'center'),
+        ('left', 'center')
+    ], ids=[
+        'left title moved',
+        'center title kept',
+        'both titles aligned'
+    ]
+)
+def test_title_above_offset(left, center):
+    # Test that title moves if overlaps with yaxis offset text.
+    mpl.rcParams['axes.titley'] = None
+    fig, ax = plt.subplots()
+    ax.set_ylim(1e11)
+    ax.set_title(left, loc='left')
+    ax.set_title(center)
+    fig.draw_without_rendering()
+    if left and not center:
+        assert ax._left_title.get_position()[1] > 1.0
+    elif not left and center:
+        assert ax.title.get_position()[1] == 1.0
+    else:
+        yleft = ax._left_title.get_position()[1]
+        ycenter = ax.title.get_position()[1]
+        assert yleft > 1.0
+        assert ycenter == yleft
+
+
 def test_title_no_move_off_page():
     # If an axes is off the figure (ie. if it is cropped during a save)
     # make sure that the automatic title repositioning does not get done.