Merge pull request matplotlib#24768 from tacaswell/fix/zorder_rasterization

Fix/zorder rasterization

Author: QuLogic

lib/matplotlib/axes/_base.py

@@ -3125,23 +3125,23 @@ def draw(self, renderer):
 
         if (rasterization_zorder is not None and
                 artists and artists[0].zorder < rasterization_zorder):
-            renderer.start_rasterizing()
-            artists_rasterized = [a for a in artists
-                                  if a.zorder < rasterization_zorder]
-            artists = [a for a in artists
-                       if a.zorder >= rasterization_zorder]
+            split_index = np.searchsorted(
+                [art.zorder for art in artists],
+                rasterization_zorder, side='right'
+            )
+            artists_rasterized = artists[:split_index]
+            artists = artists[split_index:]
         else:
             artists_rasterized = []
 
-        # the patch draws the background rectangle -- the frame below
-        # will draw the edges
         if self.axison and self._frameon:
-            self.patch.draw(renderer)
+            if artists_rasterized:
+                artists_rasterized = [self.patch] + artists_rasterized
+            else:
+                artists = [self.patch] + artists
 
         if artists_rasterized:
-            for a in artists_rasterized:
-                a.draw(renderer)
-            renderer.stop_rasterizing()
+            _draw_rasterized(self.figure, artists_rasterized, renderer)
 
         mimage._draw_list_compositing_images(
             renderer, self, artists, self.figure.suppressComposite)
@@ -4634,3 +4634,60 @@ def _label_outer_yaxis(self, *, check_patch):
             self.yaxis.set_tick_params(which="both", labelright=False)
             if self.yaxis.offsetText.get_position()[0] == 1:
                 self.yaxis.offsetText.set_visible(False)
+
+
+def _draw_rasterized(figure, artists, renderer):
+    """
+    A helper function for rasterizing the list of artists.
+
+    The bookkeeping to track if we are or are not in rasterizing mode
+    with the mixed-mode backends is relatively complicated and is now
+    handled in the matplotlib.artist.allow_rasterization decorator.
+
+    This helper defines the absolute minimum methods and attributes on a
+    shim class to be compatible with that decorator and then uses it to
+    rasterize the list of artists.
+
+    This is maybe too-clever, but allows us to re-use the same code that is
+    used on normal artists to participate in the "are we rasterizing"
+    accounting.
+
+    Please do not use this outside of the "rasterize below a given zorder"
+    functionality of Axes.
+
+    Parameters
+    ----------
+    figure : matplotlib.figure.Figure
+        The figure all of the artists belong to (not checked).  We need this
+        because we can at the figure level suppress composition and insert each
+        rasterized artist as its own image.
+
+    artists : List[matplotlib.artist.Artist]
+        The list of Artists to be rasterized.  These are assumed to all
+        be in the same Figure.
+
+    renderer : matplotlib.backendbases.RendererBase
+        The currently active renderer
+
+    Returns
+    -------
+    None
+
+    """
+    class _MinimalArtist:
+        def get_rasterized(self):
+            return True
+
+        def get_agg_filter(self):
+            return None
+
+        def __init__(self, figure, artists):
+            self.figure = figure
+            self.artists = artists
+
+        @martist.allow_rasterization
+        def draw(self, renderer):
+            for a in self.artists:
+                a.draw(renderer)
+
+    return _MinimalArtist(figure, artists).draw(renderer)

lib/matplotlib/tests/test_axes.py

@@ -8449,3 +8449,11 @@ def get_next_color():
         c = 'red\n'
         mpl.axes.Axes._parse_scatter_color_args(
             c, None, kwargs={}, xsize=2, get_next_color_func=get_next_color)
+
+
+def test_zorder_and_explicit_rasterization():
+    fig, ax = plt.subplots()
+    ax.set_rasterization_zorder(5)
+    ln, = ax.plot(range(5), rasterized=True, zorder=1)
+    with io.BytesIO() as b:
+        fig.savefig(b, format='pdf')