Cairo backend: Fix alpha render of collections

joh · joh · commit eeb63ab5ad34 · 2018-11-28T15:50:35.000+01:00
Remove RendererCairo.draw_path_collection as it made some wrong assumptions in the grouped draw optimization. Add test for the cairo backend to check rendering of path collections. Fixes #12773
diff --git a/lib/matplotlib/backends/backend_cairo.py b/lib/matplotlib/backends/backend_cairo.py
@@ -286,57 +286,6 @@ def draw_markers(self, gc, marker_path, marker_trans, path, transform,
             self._fill_and_stroke(
                 ctx, rgbFace, gc.get_alpha(), gc.get_forced_alpha())
 
-    def draw_path_collection(
-            self, gc, master_transform, paths, all_transforms, offsets,
-            offsetTrans, facecolors, edgecolors, linewidths, linestyles,
-            antialiaseds, urls, offset_position):
-
-        path_ids = [
-            (path, Affine2D(transform))
-            for path, transform in self._iter_collection_raw_paths(
-                    master_transform, paths, all_transforms)]
-
-        reuse_key = None
-        grouped_draw = []
-
-        def _draw_paths():
-            if not grouped_draw:
-                return
-            gc_vars, rgb_fc = reuse_key
-            gc = copy.copy(gc0)
-            # We actually need to call the setters to reset the internal state.
-            vars(gc).update(gc_vars)
-            for k, v in gc_vars.items():
-                if k == "_linestyle":  # Deprecated, no effect.
-                    continue
-                try:
-                    getattr(gc, "set" + k)(v)
-                except (AttributeError, TypeError) as e:
-                    pass
-            gc.ctx.new_path()
-            paths, transforms = zip(*grouped_draw)
-            grouped_draw.clear()
-            _append_paths(gc.ctx, paths, transforms)
-            self._fill_and_stroke(
-                gc.ctx, rgb_fc, gc.get_alpha(), gc.get_forced_alpha())
-
-        for xo, yo, path_id, gc0, rgb_fc in self._iter_collection(
-                gc, master_transform, all_transforms, path_ids, offsets,
-                offsetTrans, facecolors, edgecolors, linewidths, linestyles,
-                antialiaseds, urls, offset_position):
-            path, transform = path_id
-            transform = (Affine2D(transform.get_matrix())
-                         .translate(xo, yo - self.height).scale(1, -1))
-            # rgb_fc could be a ndarray, for which equality is elementwise.
-            new_key = vars(gc0), tuple(rgb_fc) if rgb_fc is not None else None
-            if new_key == reuse_key:
-                grouped_draw.append((path, transform))
-            else:
-                _draw_paths()
-                grouped_draw.append((path, transform))
-                reuse_key = new_key
-        _draw_paths()
-
     def draw_image(self, gc, x, y, im):
         im = cbook._unmultiplied_rgba8888_to_premultiplied_argb32(im[::-1])
         surface = cairo.ImageSurface.create_for_data(
diff --git a/lib/matplotlib/tests/test_backend_cairo.py b/lib/matplotlib/tests/test_backend_cairo.py
@@ -0,0 +1,55 @@
+import numpy as np
+from io import BytesIO
+import os
+import tempfile
+import warnings
+import xml.parsers.expat
+
+import pytest
+
+import matplotlib.pyplot as plt
+from matplotlib.testing.decorators import check_figures_equal
+import matplotlib
+from matplotlib import (
+    collections as mcollections, patches as mpatches, path as mpath)
+
+
+@pytest.mark.backend('cairo')
+@check_figures_equal(extensions=["png"])
+def test_patch_alpha_coloring(fig_test, fig_ref):
+    """
+    Test checks that the patch and collection are rendered with the specified
+    alpha values in their facecolor and edgecolor.
+    """
+    star = mpath.Path.unit_regular_star(6)
+    circle = mpath.Path.unit_circle()
+    # concatenate the star with an internal cutout of the circle
+    verts = np.concatenate([circle.vertices, star.vertices[::-1]])
+    codes = np.concatenate([circle.codes, star.codes])
+    cut_star1 = mpath.Path(verts, codes)
+    cut_star2 = mpath.Path(verts + 1, codes)
+
+    # Reference: two separate patches
+    ax = fig_ref.subplots()
+    ax.set_xlim([-1, 2])
+    ax.set_ylim([-1, 2])
+    patch = mpatches.PathPatch(cut_star1,
+                               linewidth=5, linestyle='dashdot',
+                               facecolor=(1, 0, 0, 0.5),
+                               edgecolor=(0, 0, 1, 0.75))
+    ax.add_patch(patch)
+    patch = mpatches.PathPatch(cut_star2,
+                               linewidth=5, linestyle='dashdot',
+                               facecolor=(1, 0, 0, 0.5),
+                               edgecolor=(0, 0, 1, 0.75))
+    ax.add_patch(patch)
+
+    # Test: path collection
+    ax = fig_test.subplots()
+    ax.set_xlim([-1, 2])
+    ax.set_ylim([-1, 2])
+    col = mcollections.PathCollection([cut_star1, cut_star2],
+                                      linewidth=5, linestyles='dashdot',
+                                      facecolor=(1, 0, 0, 0.5),
+                                      edgecolor=(0, 0, 1, 0.75))
+    ax.add_collection(col)
