From 0e95296d33ed29abb8cfdab7ad19a7aef1f61284 Mon Sep 17 00:00:00 2001
From: Antony Lee <anntzer.lee@gmail.com>
Date: Fri, 21 Jun 2019 14:44:41 +0200
Subject: [PATCH] Fix inversion of shared axes.

set_view_interval does not update shared axes, we must use
set_xlim/set_ylim to do so.

Update a test to explicitly invert an axis instead of relying on imshow
to implicitly do so.
---
 lib/matplotlib/axis.py            | 19 ++++++++++++++-----
 lib/matplotlib/tests/test_axes.py | 12 +++++++-----
 2 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
index e6293a8db830..9dc8fd6d4275 100644
--- a/lib/matplotlib/axis.py
+++ b/lib/matplotlib/axis.py
@@ -1028,11 +1028,10 @@ def set_inverted(self, inverted):
         the top for the y-axis; the "inverse" direction is increasing to the
         left for the x-axis and to the bottom for the y-axis.
         """
-        a, b = self.get_view_interval()
-        if inverted:
-            self.set_view_interval(max(a, b), min(a, b), ignore=True)
-        else:
-            self.set_view_interval(min(a, b), max(a, b), ignore=True)
+        # Currently, must be implemented in subclasses using set_xlim/set_ylim
+        # rather than generically using set_view_interval, so that shared
+        # axes get updated as well.
+        raise NotImplementedError('Derived must override')
 
     def set_default_intervals(self):
         """
@@ -2171,6 +2170,11 @@ def get_ticks_position(self):
     def get_minpos(self):
         return self.axes.dataLim.minposx
 
+    def set_inverted(self, inverted):
+        # docstring inherited
+        a, b = self.get_view_interval()
+        self.axes.set_xlim(sorted((a, b), reverse=inverted), auto=None)
+
     def set_default_intervals(self):
         # docstring inherited
         xmin, xmax = 0., 1.
@@ -2473,6 +2477,11 @@ def get_ticks_position(self):
     def get_minpos(self):
         return self.axes.dataLim.minposy
 
+    def set_inverted(self, inverted):
+        # docstring inherited
+        a, b = self.get_view_interval()
+        self.axes.set_ylim(sorted((a, b), reverse=inverted), auto=None)
+
     def set_default_intervals(self):
         # docstring inherited
         ymin, ymax = 0., 1.
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
index 0f39aaf5fdc4..6b41ed97be04 100644
--- a/lib/matplotlib/tests/test_axes.py
+++ b/lib/matplotlib/tests/test_axes.py
@@ -240,17 +240,19 @@ def test_inverted_cla():
     ax.cla()
     ax.imshow(img)
     plt.autoscale()
-    assert not(ax.xaxis_inverted())
+    assert not ax.xaxis_inverted()
     assert ax.yaxis_inverted()
 
-    # 5. two shared axes. Clearing the master axis should bring axes in shared
-    # axes back to normal
+    # 5. two shared axes. Inverting the master axis should invert the shared
+    # axes; clearing the master axis should bring axes in shared
+    # axes back to normal.
     ax0 = plt.subplot(211)
     ax1 = plt.subplot(212, sharey=ax0)
-    ax0.imshow(img)
+    ax0.yaxis.set_inverted(True)
+    assert ax1.yaxis_inverted()
     ax1.plot(x, np.cos(x))
     ax0.cla()
-    assert not(ax1.yaxis_inverted())
+    assert not ax1.yaxis_inverted()
     ax1.cla()
     # 6. clearing the nonmaster should not touch limits
     ax0.imshow(img)