fix treatment of spine paths with explicit path-codes

lib/cartopy/mpl/geoaxes.py

@@ -61,7 +61,6 @@
 # CARTOPY_USER_BACKGROUNDS environment variable.
 _USER_BG_IMGS = {}
 
-
 # XXX call this InterCRSTransform
 class InterProjectionTransform(mtransforms.Transform):
     """
@@ -229,7 +228,7 @@ def set_transform(self, transform):
         super().set_transform(self._trans_wrap)
 
     def set_boundary(self, path, transform):
-        self._original_path = path
+        self._original_path = cpatch._ensure_path_closed(path)
         self.set_transform(transform)
         self.stale = True
 
@@ -239,7 +238,9 @@ def set_path(self, path):
 
     def _adjust_location(self):
         if self.stale:
-            self.set_path(self._original_path.clip_to_bbox(self.axes.viewLim))
+            self.set_path(
+                cpatch._ensure_path_closed(
+                    self._original_path.clip_to_bbox(self.axes.viewLim)))
             # Some places in matplotlib's transform stack cache the actual
             # path so we trigger an update by invalidating the transform.
             self._trans_wrap.invalidate()
@@ -257,14 +258,16 @@ def __init__(self, axes, **kwargs):
         super().__init__(axes, 'geo', self._original_path, **kwargs)
 
     def set_boundary(self, path, transform):
-        self._original_path = path
+        # Make sure path is closed (required by "Path.clip_to_bbox")
+        self._original_path = cpatch._ensure_path_closed(path)
         self.set_transform(transform)
         self.stale = True
 
     def _adjust_location(self):
         if self.stale:
-            self._path = self._original_path.clip_to_bbox(self.axes.viewLim)
-            self._path = mpath.Path(self._path.vertices, closed=True)
+            self._path = cpatch._ensure_path_closed(
+                self._original_path.clip_to_bbox(self.axes.viewLim)
+                )
 
     def get_window_extent(self, renderer=None):
         # make sure the location is updated so that transforms etc are

lib/cartopy/mpl/patch.py

@@ -17,6 +17,37 @@
 import shapely.geometry as sgeom
 
 
+def _ensure_path_closed(path):
+    """
+    Method to ensure that a path contains only closed sub-paths.
+
+    Parameters
+    ----------
+    path
+        A :class:`matplotlib.path.Path` instance.
+
+    Returns
+    -------
+    path
+        A :class:`matplotlib.path.Path` instance with only closed polygons.
+
+    """
+    # Split path into potential sub-paths and close all polygons
+    # (explicitly disable path simplification applied in to_polygons)
+    should_simplify = path.should_simplify
+    try:
+        path.should_simplify = False
+        polygons = path.to_polygons()
+    finally:
+        path.should_simplify = should_simplify
+
+    codes, vertices = [], []
+    for poly in polygons:
+        vertices.extend([poly[0], *poly])
+        codes.extend([Path.MOVETO, *[Path.LINETO]*(len(poly) - 1), Path.CLOSEPOLY])
+
+    return Path(vertices, codes)
+
 def geos_to_path(shape):
     """
     Create a list of :class:`matplotlib.path.Path` objects that describe

lib/cartopy/tests/mpl/test_boundary.py

@@ -0,0 +1,88 @@
+# Copyright Crown and Cartopy Contributors
+#
+# This file is part of Cartopy and is released under the BSD 3-clause license.
+# See LICENSE in the root of the repository for full licensing details.
+
+from matplotlib.path import Path
+import matplotlib.pyplot as plt
+import numpy as np
+import pytest
+
+import cartopy.crs as ccrs
+
+
+circle_verts = np.array([
+    (21.33625905034713, 41.90051020408163),
+    (20.260167503134653, 36.31721708143521),
+    (17.186058185078757, 31.533809612693403),
+    (12.554340705353228, 28.235578526280886),
+    (7.02857405747471, 26.895042042418392),
+    (1.4004024147599825, 27.704250959518802),
+    (-3.5238590865749853, 30.547274662874656),
+    (-7.038740387110195, 35.0168098237746),
+    (-8.701144846177232, 41.42387784534415),
+    (-7.802741418346137, 47.03850217758886),
+    (-4.224119444187849, 52.606946662776494),
+    (0.5099122186645388, 55.75656240544797),
+    (6.075429329647158, 56.92110282927732),
+    (11.675092899771812, 55.933731058974054),
+    (16.50667197715324, 52.93590205611499),
+    (19.87797456957319, 48.357097196578444),
+    (21.33625905034713, 41.90051020408163)
+    ])
+
+circle_codes = [
+    Path.MOVETO,
+    *[Path.LINETO]*(len(circle_verts)),
+    Path.CLOSEPOLY
+    ]
+
+rectangle_verts = np.array([
+    (55.676020408163225, 36.16071428571428),
+    (130.29336734693877, 36.16071428571428),
+    (130.29336734693877, -4.017857142857167),
+    (55.676020408163225, -4.017857142857167),
+    (55.676020408163225, 36.16071428571428)
+    ])
+
+rectangle_codes = [
+    Path.MOVETO,
+    *[Path.LINETO]*(len(rectangle_verts)),
+    Path.CLOSEPOLY
+    ]
+
+
+@pytest.mark.natural_earth
+@pytest.mark.mpl_image_compare(filename='multi_path_boundary.png')
+def test_multi_path_boundary():
+    offsets = np.array([[30, 30], [70, 30], [110, 20]])
+
+    closed = [True, False, False]
+
+    vertices, codes = [], []
+    # add closed and open circles
+    for offset, close in zip(offsets, closed):
+        c = circle_verts + offset
+        if close:
+            vertices.extend([c[0], *c, c[-1]])
+            codes.extend([Path.MOVETO, *[Path.LINETO]*len(c), Path.CLOSEPOLY])
+        else:
+            vertices.extend([c[0], *c])
+            codes.extend([Path.MOVETO, *[Path.LINETO]*len(c)])
+
+    # add rectangle
+    vertices.extend(
+        [rectangle_verts[0], *rectangle_verts, rectangle_verts[-1]]
+        )
+    codes.extend(
+        [Path.MOVETO, *[Path.LINETO]*len(rectangle_verts), Path.CLOSEPOLY]
+        )
+
+    bnds = [*map(min, zip(*vertices)), *map(max, zip(*vertices))]
+
+    f, ax = plt.subplots(subplot_kw=dict(projection=ccrs.PlateCarree()))
+    ax.set_extent((bnds[0], bnds[2], bnds[1], bnds[3]))
+    ax.coastlines()
+    ax.set_boundary(Path(vertices, codes))
+
+    return f