matplotlib · ayshih · Jul 8, 2026 · Jul 8, 2026
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/preset_clip_paths.png b/lib/matplotlib/tests/baseline_images/test_axes/preset_clip_paths.png
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/sticky_tolerance_cf.png b/lib/matplotlib/tests/baseline_images/test_axes/sticky_tolerance_cf.png
diff --git a/lib/matplotlib/tests/baseline_images/test_colorbar/double_cbar.png b/lib/matplotlib/tests/baseline_images/test_colorbar/double_cbar.png
diff --git a/...b/tests/baseline_images/test_constrainedlayout/test_submerged_with_colorbar.png b/...b/tests/baseline_images/test_constrainedlayout/test_submerged_with_colorbar.png
diff --git a/lib/matplotlib/tests/baseline_images/test_contour/contour_datetime_axis.png b/lib/matplotlib/tests/baseline_images/test_contour/contour_datetime_axis.png
diff --git a/...plotlib/tests/baseline_images/test_contour/contour_manual_colors_and_levels.png b/...plotlib/tests/baseline_images/test_contour/contour_manual_colors_and_levels.png
diff --git a/lib/matplotlib/tests/baseline_images/test_contour/contourf_hatch_colors.png b/lib/matplotlib/tests/baseline_images/test_contour/contourf_hatch_colors.png
diff --git a/lib/matplotlib/tests/baseline_images/test_triangulation/tripcolor1.png b/lib/matplotlib/tests/baseline_images/test_triangulation/tripcolor1.png
diff --git a/lib/matplotlib/tests/test_agg.py b/lib/matplotlib/tests/test_agg.py
@@ -13,8 +13,9 @@
 from matplotlib.backends.backend_agg import RendererAgg
 from matplotlib.figure import Figure
 from matplotlib.image import imread
+from matplotlib.patches import PathPatch, Polygon
 from matplotlib.path import Path
-from matplotlib.testing.decorators import image_comparison
+from matplotlib.testing.decorators import check_figures_equal, image_comparison
 from matplotlib.transforms import IdentityTransform
 
 
@@ -387,3 +388,40 @@ def test_non_tuple_rgbaface():
     fig.add_subplot(projection="3d").scatter(
         [0, 1, 2], [0, 1, 2], path_effects=[patheffects.Stroke(linewidth=4)])
     fig.canvas.draw()
+
+
+@check_figures_equal()
+def test_path_autosnap(fig_test, fig_ref):
+    axt = fig_test.subplots()
+    axr = fig_ref.subplots()
+
+    square = np.array([[0, 0], [1, 0], [1, 1], [0, 1]])
+    triangle1 = np.array([[0, 2], [1, 2], [0, 3]])
+    triangle2 = np.array([[0, 4], [1, 4], [1, 3]])
+
+    # A square should autosnap
+    axt.add_patch(Polygon(square, snap=None))
+    axr.add_patch(Polygon(square, snap=True))
+
+    # A triangle with the diagonal as one of the line segments should not autosnap
+    axt.add_patch(Polygon(triangle1, snap=None))
+    axr.add_patch(Polygon(triangle1, snap=False))
+
+    # A triangle with the diagonal as the closing line segment should not autosnap
+    axt.add_patch(Polygon(triangle2, snap=None))
+    axr.add_patch(Polygon(triangle2, snap=False))
+
+    # A path of multiple polygons should autosnap if each polygon would autosnap
+    multiple1 = Path.make_compound_path(Polygon(square + [[2, 0]]).get_path(),
+                                        Polygon(square + [[2, 2]]).get_path())
+    axt.add_patch(PathPatch(multiple1, edgecolor='none', snap=None))
+    axr.add_patch(PathPatch(multiple1, edgecolor='none', snap=True))
+
+    # A path of multiple polygons should not autosnap if any polygon would not autosnap
+    multiple2 = Path.make_compound_path(Polygon(square + [[4, 0]]).get_path(),
+                                        Polygon(triangle1 + [[4, 0]]).get_path())
+    axt.add_patch(PathPatch(multiple2, edgecolor='none', snap=None))
+    axr.add_patch(PathPatch(multiple2, edgecolor='none', snap=False))
+
+    axt.autoscale_view()
+    axr.autoscale_view()
diff --git a/src/path_converters.h b/src/path_converters.h
@@ -560,7 +560,7 @@ class PathSnapper
     {
         // If this contains only straight horizontal or vertical lines, it should be
         // snapped to the nearest pixels
-        double x0 = 0, y0 = 0, x1 = 0, y1 = 0;
+        double xi = 0, yi = 0, x0 = 0, y0 = 0, x1 = 0, y1 = 0;
         unsigned code;
 
         switch (snap_mode) {
@@ -574,6 +574,10 @@ class PathSnapper
                 return false;
             }
 
+            // Store the initial vertex in case the path gets closed
+            xi = x0;
+            yi = y0;
+
             while ((code = path.vertex(&x1, &y1)) != agg::path_cmd_stop) {
                 switch (code) {
                 case agg::path_cmd_curve3:
@@ -583,6 +587,17 @@ class PathSnapper
                     if (fabs(x0 - x1) >= 1e-4 && fabs(y0 - y1) >= 1e-4) {
                         return false;
                     }
+                    break;
+                case (agg::path_cmd_end_poly | agg::path_flags_close):
+                    if (fabs(x0 - xi) >= 1e-4 && fabs(y0 - yi) >= 1e-4) {
+                        return false;
+                    }
+                    break;
+                case agg::path_cmd_move_to:
+                    // Update the initial vertex for a new sub-path
+                    xi = x1;
+                    yi = y1;
+                    break;
                 }
                 x0 = x1;
                 y0 = y1;