Merge pull request matplotlib#27334 from ksunden/contour-moveto

Omit MOVETO lines from nearest contour logic

Author: tacaswell

lib/matplotlib/contour.py

@@ -1339,15 +1339,18 @@ def _find_nearest_contour(self, xy, indices=None):
 
         for idx_level in indices:
             path = self._paths[idx_level]
-            if not len(path.vertices):
-                continue
-            lc = self.get_transform().transform(path.vertices)
-            d2, proj, leg = _find_closest_point_on_path(lc, xy)
-            if d2 < d2min:
-                d2min = d2
-                idx_level_min = idx_level
-                idx_vtx_min = leg[1]
-                proj_min = proj
+            idx_vtx_start = 0
+            for subpath in path._iter_connected_components():
+                if not len(subpath.vertices):
+                    continue
+                lc = self.get_transform().transform(subpath.vertices)
+                d2, proj, leg = _find_closest_point_on_path(lc, xy)
+                if d2 < d2min:
+                    d2min = d2
+                    idx_level_min = idx_level
+                    idx_vtx_min = leg[1] + idx_vtx_start
+                    proj_min = proj
+                idx_vtx_start += len(subpath)
 
         return idx_level_min, idx_vtx_min, proj_min
 

lib/matplotlib/tests/test_contour.py

@@ -125,6 +125,25 @@ def test_contour_manual_labels(split_collections):
     plt.clabel(cs, manual=pts, fontsize='small', colors=('r', 'g'))
 
 
+def test_contour_manual_moveto():
+    x = np.linspace(-10, 10)
+    y = np.linspace(-10, 10)
+
+    X, Y = np.meshgrid(x, y)
+
+    Z = X**2 * 1 / Y**2 - 1
+
+    contours = plt.contour(X, Y, Z, levels=[0, 100])
+
+    # This point lies on the `MOVETO` line for the 100 contour
+    # but is actually closest to the 0 contour
+    point = (1.3, 1)
+    clabels = plt.clabel(contours, manual=[point])
+
+    # Ensure that the 0 contour was chosen, not the 100 contour
+    assert clabels[0].get_text() == "0"
+
+
 @pytest.mark.parametrize("split_collections", [False, True])
 @image_comparison(['contour_disconnected_segments'],
                   remove_text=True, style='mpl20', extensions=['png'])