Add path code information to Poly3DCollection

Fixes matplotlib#4784 by adding path code information to the Poly3DCollection.
This adds two new methods, path_to_3d_segment_with_codes and
paths_to_3d_segments_with_codes which are meant to replace the
versions without "_with_codes".  A method was added to PolyCollection
to allow Poly3DCollection to set vertices with path codes.

Add image test for a case that causes improper polygon rendering
without this fix.

This code was adapted from a PR by @ianthomas23.

doc/users/whats_new/plotting.rst

@@ -29,3 +29,13 @@ points are contoured as usual.  If the ``corner_mask`` keyword argument is not
 specified, the default value is taken from rcParams.
 
 .. plot:: mpl_examples/pylab_examples/contour_corner_mask.py
+
+Fixed 3D filled contour plot polygon rendering
+``````````````````````````````````````````````
+
+Certain cases of 3D filled contour plots that produce polygons with multiple
+holes produced improper rendering due to a loss of path information between
+:class:`~matplotlib.collections.PolyCollection` and 
+:class:`~mpl_toolkits.mplot3d.art3d.Poly3DCollection`.  A function
+:func:`~matplotlib.collections.PolyCollection.set_verts_and_codes` was
+added to allow path information to be retained for proper rendering.

lib/matplotlib/collections.py

@@ -888,6 +888,19 @@ def set_verts(self, verts, closed=True):
 
     set_paths = set_verts
 
+    def set_verts_and_codes(self, verts, codes):
+        '''This allows one to initialize vertices with path codes.'''
+        if (len(verts) != len(codes)):
+            raise ValueError("'codes' must be a 1D list or array "
+                             "with the same length of 'verts'")
+        self._paths = []
+        for xy, cds in zip(verts, codes):
+            if len(xy):
+                self._paths.append(mpath.Path(xy, cds))
+            else:
+                self._paths.append(mpath.Path(xy))
+        self.stale = True
+
 
 class BrokenBarHCollection(PolyCollection):
     """

lib/mpl_toolkits/mplot3d/art3d.py

@@ -166,6 +166,37 @@ def paths_to_3d_segments(paths, zs=0, zdir='z'):
         segments.append(path_to_3d_segment(path, pathz, zdir))
     return segments
 
+def path_to_3d_segment_with_codes(path, zs=0, zdir='z'):
+    '''Convert a path to a 3D segment with path codes.'''
+
+    if not iterable(zs):
+        zs = np.ones(len(path)) * zs
+
+    seg = []
+    codes = []
+    pathsegs = path.iter_segments(simplify=False, curves=False)
+    for (((x, y), code), z) in zip(pathsegs, zs):
+        seg.append((x, y, z))
+        codes.append(code)
+    seg3d = [juggle_axes(x, y, z, zdir) for (x, y, z) in seg]
+    return seg3d, codes
+
+def paths_to_3d_segments_with_codes(paths, zs=0, zdir='z'):
+    '''
+    Convert paths from a collection object to 3D segments with path codes.
+    '''
+
+    if not iterable(zs):
+        zs = np.ones(len(paths)) * zs
+
+    segments = []
+    codes_list = []
+    for path, pathz in zip(paths, zs):
+        segs, codes = path_to_3d_segment_with_codes(path, pathz, zdir)
+        segments.append(segs)
+        codes_list.append(codes)
+    return segments, codes_list
+
 class Line3DCollection(LineCollection):
     '''
     A collection of 3D lines.
@@ -487,6 +518,7 @@ def __init__(self, verts, *args, **kwargs):
         zsort = kwargs.pop('zsort', True)
         PolyCollection.__init__(self, verts, *args, **kwargs)
         self.set_zsort(zsort)
+        self._codes3d = None
 
     _zsort_functions = {
         'average': np.average,
@@ -545,6 +577,14 @@ def set_verts(self, verts, closed=True):
         # 2D verts will be updated at draw time
         PolyCollection.set_verts(self, [], closed)
 
+    def set_verts_and_codes(self, verts, codes):
+        '''Sets 3D vertices with path codes'''
+        # set vertices with closed=False to prevent PolyCollection from
+        # setting path codes
+        self.set_verts(verts, closed=False)
+        # and set our own codes instead.
+        self._codes3d = codes
+
     def set_3d_properties(self):
         # Force the collection to initialize the face and edgecolors
         # just in case it is a scalarmappable with a colormap.
@@ -571,8 +611,8 @@ def do_3d_projection(self, renderer):
             self._facecolors3d = self._facecolors
 
         txs, tys, tzs = proj3d.proj_transform_vec(self._vec, renderer.M)
-        xyzlist = [(txs[si:ei], tys[si:ei], tzs[si:ei]) \
-                for si, ei in self._segis]
+        xyzlist = [(txs[si:ei], tys[si:ei], tzs[si:ei])
+                   for si, ei in self._segis]
 
         # This extra fuss is to re-order face / edge colors
         cface = self._facecolors3d
@@ -586,18 +626,24 @@ def do_3d_projection(self, renderer):
 
         # if required sort by depth (furthest drawn first)
         if self._zsort:
-            z_segments_2d = [(self._zsortfunc(zs), list(zip(xs, ys)), fc, ec) for
-                    (xs, ys, zs), fc, ec in zip(xyzlist, cface, cedge)]
+            indices = range(len(xyzlist))
+            z_segments_2d = [(self._zsortfunc(zs), list(zip(xs, ys)), fc, ec,
+                              idx) for (xs, ys, zs), fc, ec, idx in
+                             zip(xyzlist, cface, cedge, indices)]
             z_segments_2d.sort(key=lambda x: x[0], reverse=True)
         else:
             raise ValueError("whoops")
 
-        segments_2d = [s for z, s, fc, ec in z_segments_2d]
-        PolyCollection.set_verts(self, segments_2d)
+        segments_2d = [s for z, s, fc, ec, idx in z_segments_2d]
+        if self._codes3d is not None:
+            codes = [self._codes3d[idx] for z, s, fc, ec, idx in z_segments_2d]
+            PolyCollection.set_verts_and_codes(self, segments_2d, codes)
+        else:
+            PolyCollection.set_verts(self, segments_2d)
 
-        self._facecolors2d = [fc for z, s, fc, ec in z_segments_2d]
+        self._facecolors2d = [fc for z, s, fc, ec, idx in z_segments_2d]
         if len(self._edgecolors3d) == len(cface):
-            self._edgecolors2d = [ec for z, s, fc, ec in z_segments_2d]
+            self._edgecolors2d = [ec for z, s, fc, ec, idx in z_segments_2d]
         else:
             self._edgecolors2d = self._edgecolors3d
 
@@ -663,9 +709,10 @@ def draw(self, renderer):
 
 def poly_collection_2d_to_3d(col, zs=0, zdir='z'):
     """Convert a PolyCollection to a Poly3DCollection object."""
-    segments_3d = paths_to_3d_segments(col.get_paths(), zs, zdir)
+    segments_3d, codes = paths_to_3d_segments_with_codes(col.get_paths(),
+                                                         zs, zdir)
     col.__class__ = Poly3DCollection
-    col.set_verts(segments_3d)
+    col.set_verts_and_codes(segments_3d, codes)
     col.set_3d_properties()
 
 def juggle_axes(xs, ys, zs, zdir):