Fixes matplotlib#1860: Unfilled members of collections are not handle…

…d correctly in the PDF backend. Also fixes a related bug that alpha could not be set on individual members of a collection.

lib/matplotlib/backend_bases.py

@@ -352,6 +352,8 @@ def _iter_collection(self, gc, master_transform, all_transforms,
         gc0 = self.new_gc()
         gc0.copy_properties(gc)
 
+        original_alpha = gc.get_alpha()
+
         if Nfacecolors == 0:
             rgbFace = None
 
@@ -374,22 +376,28 @@ def _iter_collection(self, gc, master_transform, all_transforms,
                     yo = -(yp - yo)
             if not (np.isfinite(xo) and np.isfinite(yo)):
                 continue
+            gc0.set_alpha(original_alpha)
             if Nfacecolors:
                 rgbFace = facecolors[i % Nfacecolors]
             if Nedgecolors:
-                fg = edgecolors[i % Nedgecolors]
-                if Nfacecolors == 0 and len(fg)==4:
-                    gc0.set_alpha(fg[3])
-                gc0.set_foreground(fg)
                 if Nlinewidths:
                     gc0.set_linewidth(linewidths[i % Nlinewidths])
                 if Nlinestyles:
                     gc0.set_dashes(*linestyles[i % Nlinestyles])
-            if rgbFace is not None and len(rgbFace)==4:
+                fg = edgecolors[i % Nedgecolors]
+                if len(fg) == 4:
+                    if fg[3] == 0.0:
+                        gc0.set_linewidth(0)
+                    else:
+                        gc0.set_alpha(gc0.get_alpha() * fg[3])
+                        gc0.set_foreground(fg[:3])
+                else:
+                    gc0.set_foreground(fg)
+            if rgbFace is not None and len(rgbFace) == 4:
                 if rgbFace[3] == 0:
                     rgbFace = None
                 else:
-                    gc0.set_alpha(rgbFace[3])
+                    gc0.set_alpha(gc0.get_alpha() * rgbFace[3])
                     rgbFace = rgbFace[:3]
             gc0.set_antialiased(antialiaseds[i % Naa])
             if Nurls:

lib/matplotlib/backends/backend_pdf.py

@@ -1523,10 +1523,36 @@ def draw_path_collection(self, gc, master_transform, paths, all_transforms,
                              offsets, offsetTrans, facecolors, edgecolors,
                              linewidths, linestyles, antialiaseds, urls,
                              offset_position):
+        # We can only reuse the objects if the presence of fill and
+        # stroke (and the amount of alpha for each) is the same for
+        # all of them
+        can_do_optimization = True
+
+        if not len(facecolors):
+            filled = False
+        else:
+            if np.all(facecolors[:, 3] == facecolors[0, 3]):
+                filled = facecolors[0, 3] != 0.0
+            else:
+                can_do_optimization = False
+
+        if not len(edgecolors):
+            stroked = False
+        else:
+            if np.all(edgecolors[:, 3] == edgecolors[0, 3]):
+                stroked = edgecolors[0, 3] != 0.0
+            else:
+                can_do_optimization = False
+
+        if not can_do_optimization:
+            return RendererBase.draw_path_collection(
+                self, gc, master_transform, paths, all_transforms,
+                offsets, offsetTrans, facecolors, edgecolors,
+                linewidths, linestyles, antialiaseds, urls,
+                offset_position)
+
         padding = np.max(linewidths)
         path_codes = []
-        filled = len(facecolors)
-        stroked = len(edgecolors)
         for i, (path, transform) in enumerate(self._iter_collection_raw_paths(
             master_transform, paths, all_transforms)):
             name = self.file.pathCollectionObject(