Hide fully transparent text in PS output.

anntzer · anntzer · commit ee043fce0ee3 · 2018-01-04T14:11:59.000-08:00
PS doesn't really support transparency (because the format itself
doesn't, unless using some nonstandard extensions), but has some special
casing for "fully transparent" (see e.g. "rgbFace is None" check in
_draw_ps).

Also implement the special-casing for text.
diff --git a/lib/matplotlib/backends/backend_ps.py b/lib/matplotlib/backends/backend_ps.py
@@ -631,13 +631,16 @@ def draw_tex(self, gc, x, y, s, prop, angle, ismath='TeX!', mtext=None):
 
     def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
         """
-        draw a Text instance
+        Draw a Text instance.
         """
         # local to avoid repeated attribute lookups
         write = self._pswriter.write
         if debugPS:
             write("% text\n")
 
+        if len(gc.get_rgb()) == 4 and gc.get_rgb()[3] == 0:
+            return  # Special handling for fully transparent.
+
         if ismath=='TeX':
             return self.draw_tex(gc, x, y, s, prop, angle)
 
diff --git a/lib/matplotlib/tests/baseline_images/test_backend_ps/empty.pdf b/lib/matplotlib/tests/baseline_images/test_backend_ps/empty.pdf
diff --git a/lib/matplotlib/tests/test_backend_ps.py b/lib/matplotlib/tests/test_backend_ps.py
@@ -12,6 +12,7 @@
 import matplotlib
 import matplotlib.pyplot as plt
 from matplotlib import patheffects
+from matplotlib.testing.decorators import image_comparison
 from matplotlib.testing.determinism import (_determinism_source_date_epoch,
                                             _determinism_check)
 
@@ -148,3 +149,11 @@ def test_determinism_all():
 def test_determinism_all_tex():
     """Test for reproducible PS/tex output"""
     _determinism_check(format="ps", usetex=True)
+
+
+@image_comparison(baseline_images=["empty"], extensions=["eps"])
+def test_transparency():
+    fig, ax = plt.subplots()
+    ax.set_axis_off()
+    ax.plot([0, 1], color="r", alpha=0)
+    ax.text(.5, .5, "foo", color="r", alpha=0)
