BUG: Fix stale rendering on MacOSX backend (Fixes #8282)

dopplershift · dopplershift · commit dc7a95123b2d · 2017-10-23T17:58:48.000-06:00
Unlike on other backends (like Qt), MacOSX backend was never telling the
renderer to clear. This resulted in draws that would happen on top of
the previous Agg buffer. It seems enough to clear the renderer if the
figure is stale.
diff --git a/lib/matplotlib/backends/backend_macosx.py b/lib/matplotlib/backends/backend_macosx.py
@@ -77,10 +77,11 @@ def _set_device_scale(self, value):
             self._device_scale = value
 
     def _draw(self):
-        renderer = self.get_renderer()
-
         if self.figure.stale:
+            renderer = self.get_renderer(cleared=True)
             self.figure.draw(renderer)
+        else:
+            renderer = self.get_renderer()
 
         return renderer
 
