Avoid title overlap with abc labels

ultraplot/axes/base.py

@@ -2986,6 +2986,8 @@ def _update_title(self, loc, title=None, **kwargs):
                 kw["text"] = title[self.number - 1]
         else:
             raise ValueError(f"Invalid title {title!r}. Must be string(s).")
+        if any(key in kwargs for key in ("size", "fontsize")):
+            self._title_dict[loc]._ultraplot_manual_size = True
         kw.update(kwargs)
         self._title_dict[loc].update(kw)
 
@@ -3042,7 +3044,9 @@ def _update_title_position(self, renderer):
         # Offset title away from a-b-c label
         atext, ttext = aobj.get_text(), tobj.get_text()
         awidth = twidth = 0
-        pad = (abcpad / 72) / self._get_size_inches()[0]
+        width_inches = self._get_size_inches()[0]
+        pad = (abcpad / 72) / width_inches
+        abc_pad = (self._abc_pad / 72) / width_inches
         ha = aobj.get_ha()
 
         # Get dimensions of non-empty elements
@@ -3059,6 +3063,36 @@ def _update_title_position(self, renderer):
                 .width
             )
 
+        # Shrink the title font if both texts share a location and would overflow
+        if (
+            atext
+            and ttext
+            and self._abc_loc == self._title_loc
+            and twidth > 0
+            and not getattr(tobj, "_ultraplot_manual_size", False)
+        ):
+            scale = 1
+            base_x = tobj.get_position()[0]
+            if ha == "left":
+                available = 1 - (base_x + awidth + pad)
+                if available < twidth and available > 0:
+                    scale = available / twidth
+            elif ha == "right":
+                available = base_x + abc_pad - pad - awidth
+                if available < twidth and available > 0:
+                    scale = available / twidth
+            elif ha == "center":
+                # Conservative fit for centered titles sharing the abc location
+                left_room = base_x - 0.5 * (awidth + pad)
+                right_room = 1 - (base_x + 0.5 * (awidth + pad))
+                max_room = min(left_room, right_room)
+                if max_room < twidth / 2 and max_room > 0:
+                    scale = (2 * max_room) / twidth
+
+            if scale < 1:
+                tobj.set_fontsize(tobj.get_fontsize() * scale)
+                twidth *= scale
+
         # Calculate offsets based on alignment and content
         aoffset = toffset = 0
         if atext and ttext:

ultraplot/tests/test_axes.py

@@ -4,6 +4,7 @@
 """
 import numpy as np
 import pytest
+
 import ultraplot as uplt
 from ultraplot.internals.warnings import UltraPlotWarning
 
@@ -130,6 +131,35 @@ def test_cartesian_format_all_units_types():
     ax.format(**kwargs)
 
 
+def test_title_shrinks_when_abc_overlaps():
+    """
+    Ensure long titles shrink when they would overlap the abc label.
+    """
+    fig, ax = uplt.subplots(figsize=(2, 2))
+    ax.format(abc=True, title="X" * 200, titleloc="left", abcloc="left")
+    title_obj = ax._title_dict["left"]
+    original_size = title_obj.get_fontsize()
+    fig.canvas.draw()
+    assert title_obj.get_fontsize() < original_size
+
+
+def test_title_manual_size_ignores_auto_shrink():
+    """
+    Ensure explicit title sizes bypass auto-scaling.
+    """
+    fig, ax = uplt.subplots(figsize=(2, 2))
+    ax.format(
+        abc=True,
+        title="X" * 200,
+        titleloc="left",
+        abcloc="left",
+        title_kw={"size": 20},
+    )
+    title_obj = ax._title_dict["left"]
+    fig.canvas.draw()
+    assert title_obj.get_fontsize() == 20
+
+
 def test_axis_access():
     # attempt to access the ax object 2d and linearly
     fig, ax = uplt.subplots(ncols=2, nrows=2)