Abc title space fix

ultraplot/axes/container.py

@@ -17,6 +17,8 @@
 
 __all__ = ["ExternalAxesContainer"]
 
+_ABOVE_AXES_TITLE_LOCS = {"left", "center", "right"}
+
 
 class ExternalAxesContainer(CartesianAxes):
     """
@@ -399,7 +401,9 @@ def _ensure_external_fits_within_container(self, renderer):
         container_bbox = container_pos.transformed(self.figure.transFigure)
         # Reserve vertical space for titles/abc labels.
         title_pad_px = 0.0
-        for obj in self._title_dict.values():
+        for loc, obj in self._title_dict.items():
+            if not self._title_reserves_external_space(loc):
+                continue
             if not obj.get_visible():
                 continue
             if not obj.get_text():
@@ -548,14 +552,24 @@ def _update_title_position(self, renderer):
         container_bbox = self.get_position().transformed(fig.transFigure)
         if container_bbox.height <= 0:
             return
-        for obj in self._title_dict.values():
+        for loc, obj in self._title_dict.items():
+            if not self._title_reserves_external_space(loc):
+                continue
             bbox = obj.get_window_extent(renderer)
             overflow = bbox.y1 - container_bbox.y1
             if overflow > 0:
                 x, y = obj.get_position()
                 y -= overflow / container_bbox.height
                 obj.set_position((x, y))
 
+    def _title_reserves_external_space(self, loc):
+        """
+        Return whether a title-like artist needs room above an external axes.
+        """
+        if loc == "abc":
+            loc = self._abc_loc
+        return loc in _ABOVE_AXES_TITLE_LOCS
+
     def _iter_axes(self, hidden=True, children=True, panels=True):
         """
         Override to only yield the container itself, not the external axes.

ultraplot/tests/test_external_container_edge_cases.py

@@ -666,6 +666,53 @@ def points_to_pixels(self, value):
     assert new_pos.height <= initial_pos.height
 
 
+class ContainerTightBboxAxes(MinimalExternalAxes):
+    """External axes whose tight bbox exactly matches its current position."""
+
+    def get_tightbbox(self, renderer):
+        return self._position.transformed(self.figure.transFigure)
+
+
+def _external_position_after_abc_fit(abcloc):
+    fig = uplt.figure()
+    ax = ExternalAxesContainer(
+        fig,
+        1,
+        1,
+        1,
+        external_axes_class=ContainerTightBboxAxes,
+        external_axes_kwargs={},
+        external_padding=0.0,
+        external_shrink_factor=1.0,
+    )
+    ax.number = 1
+    ax.format(abc="A", abcloc=abcloc)
+
+    child = ax.get_external_child()
+    child.set_position(ax.get_position())
+    initial_pos = child.get_position().frozen()
+    renderer = fig.canvas.get_renderer()
+    ax._update_title_position(renderer)
+    ax._ensure_external_fits_within_container(renderer)
+    return initial_pos, child.get_position()
+
+
+def test_inside_abc_location_does_not_reserve_external_title_space():
+    """Inside abc labels should not shrink the external axes title area."""
+    initial_pos, new_pos = _external_position_after_abc_fit("upper left")
+
+    assert new_pos.height == pytest.approx(initial_pos.height)
+    assert new_pos.y0 == pytest.approx(initial_pos.y0)
+
+
+def test_above_axes_abc_location_reserves_external_title_space():
+    """Above-axes abc labels should still leave room above external axes."""
+    initial_pos, new_pos = _external_position_after_abc_fit("left")
+
+    assert new_pos.height < initial_pos.height
+    assert new_pos.y0 > initial_pos.y0
+
+
 def test_external_axes_fallback_to_rect_on_typeerror():
     """Test fallback to rect init when subplotspec is unsupported."""
     fig = uplt.figure()