Merge pull request matplotlib#26101 from QuLogic/text-marker-centre

Correct bounding box calculation for text markers

Author: oscargus

lib/matplotlib/markers.py

@@ -509,14 +509,12 @@ def _set_mathtext_path(self):
         if len(text.vertices) == 0:
             return
 
-        xmin, ymin = text.vertices.min(axis=0)
-        xmax, ymax = text.vertices.max(axis=0)
-        width = xmax - xmin
-        height = ymax - ymin
-        max_dim = max(width, height)
-        self._transform = Affine2D() \
-            .translate(-xmin + 0.5 * -width, -ymin + 0.5 * -height) \
-            .scale(1.0 / max_dim)
+        bbox = text.get_extents()
+        max_dim = max(bbox.width, bbox.height)
+        self._transform = (
+            Affine2D()
+            .translate(-bbox.xmin + 0.5 * -bbox.width, -bbox.ymin + 0.5 * -bbox.height)
+            .scale(1.0 / max_dim))
         self._path = text
         self._snap = False
 

lib/matplotlib/tests/test_marker.py

@@ -156,6 +156,18 @@ def draw_ref_marker(y, style, size):
     ax_ref.set(xlim=(-0.5, 1.5), ylim=(-0.5, 1.5))
 
 
+# The bullet mathtext marker is not quite a circle, so this is not a perfect match, but
+# it is close enough to confirm that the text-based marker is centred correctly. But we
+# still need a small tolerance to work around that difference.
+@check_figures_equal(extensions=['png'], tol=1.86)
+def test_text_marker(fig_ref, fig_test):
+    ax_ref = fig_ref.add_subplot()
+    ax_test = fig_test.add_subplot()
+
+    ax_ref.plot(0, 0, marker=r'o', markersize=100, markeredgewidth=0)
+    ax_test.plot(0, 0, marker=r'$\bullet$', markersize=100, markeredgewidth=0)
+
+
 @check_figures_equal()
 def test_marker_clipping(fig_ref, fig_test):
     # Plotting multiple markers can trigger different optimized paths in