matplotlib · QuLogic · Aug 19, 2022 · Aug 17, 2022 · Aug 18, 2022 · Aug 18, 2022
diff --git a/lib/mpl_toolkits/mplot3d/axis3d.py b/lib/mpl_toolkits/mplot3d/axis3d.py
@@ -244,11 +244,23 @@ def _get_coord_info(self, renderer):
         bounds_proj = self.axes.tunit_cube(bounds, self.axes.M)
 
         # Determine which one of the parallel planes are higher up:
-        highs = np.zeros(3, dtype=bool)
+        means_z0 = np.zeros(3)
+        means_z1 = np.zeros(3)
         for i in range(3):
-            mean_z0 = np.mean(bounds_proj[self._PLANES[2 * i], 2])
-            mean_z1 = np.mean(bounds_proj[self._PLANES[2 * i + 1], 2])
-            highs[i] = mean_z0 < mean_z1
+            means_z0[i] = np.mean(bounds_proj[self._PLANES[2 * i], 2])
+            means_z1[i] = np.mean(bounds_proj[self._PLANES[2 * i + 1], 2])
+        highs = means_z0 < means_z1
+
+        # Special handling for edge-on views
+        equals = np.abs(means_z0 - means_z1) <= np.finfo(float).eps
+        if np.sum(equals) == 2:
+            vertical = np.where(~equals)[0][0]
+            if vertical == 2:  # looking at XY plane
+                highs = np.array([True, True, highs[2]])
+            elif vertical == 1:  # looking at XZ plane
+                highs = np.array([True, highs[1], False])
+            elif vertical == 0:  # looking at YZ plane
+                highs = np.array([highs[0], False, False])
 
         return mins, maxs, centers, deltas, bounds_proj, highs
 

diff --git a/lib/mpl_toolkits/tests/baseline_images/test_mplot3d/axes3d_primary_views.png b/lib/mpl_toolkits/tests/baseline_images/test_mplot3d/axes3d_primary_views.png
diff --git a/lib/mpl_toolkits/tests/baseline_images/test_mplot3d/axes3d_rotated.png b/lib/mpl_toolkits/tests/baseline_images/test_mplot3d/axes3d_rotated.png
diff --git a/lib/mpl_toolkits/tests/test_mplot3d.py b/lib/mpl_toolkits/tests/test_mplot3d.py
@@ -60,6 +60,27 @@ def test_axes3d_repr():
         "title={'center': 'title'}, xlabel='x', ylabel='y', zlabel='z'>")
 
 
+@mpl3d_image_comparison(['axes3d_primary_views.png'])
+def test_axes3d_primary_views():
+    # (elev, azim, roll)
+    views = [(90, -90, 0),  # XY
+             (0, -90, 0),   # XZ
+             (0, 0, 0),     # YZ
+             (-90, 90, 0),  # -XY
+             (0, 90, 0),    # -XZ
+             (0, 180, 0)]   # -YZ
+    # When viewing primary planes, draw the two visible axes so they intersect
+    # at their low values
+    fig, axs = plt.subplots(2, 3, subplot_kw={'projection': '3d'})
+    for i, ax in enumerate(axs.flat):
+        ax.set_xlabel('x')
+        ax.set_ylabel('y')
+        ax.set_zlabel('z')
+        ax.set_proj_type('ortho')
+        ax.view_init(elev=views[i][0], azim=views[i][1], roll=views[i][2])
+    plt.tight_layout()
+
+
 @mpl3d_image_comparison(['bar3d.png'])
 def test_bar3d():
     fig = plt.figure()
@@ -1839,9 +1860,9 @@ def test_scatter_spiral():
                 [0.0, 0.0, -1.142857, 10.571429],
             ],
             [
-                ([0.06329114, -0.06329114], [-0.04746835, -0.04746835]),
-                ([-0.06329114, -0.06329114], [0.04746835, -0.04746835]),
-                ([0.05617978, 0.06329114], [-0.04213483, -0.04746835]),
+                ([-0.06329114, 0.06329114], [0.04746835, 0.04746835]),
+                ([0.06329114, 0.06329114], [-0.04746835, 0.04746835]),
+                ([-0.05617978, -0.06329114], [0.04213483, 0.04746835]),
             ],
             [2, 2, 0],
         ),
@@ -1854,9 +1875,9 @@ def test_scatter_spiral():
                 [0.0, -1.142857, 0.0, 10.571429],
             ],
             [
-                ([-0.06329114, -0.06329114], [-0.04746835, 0.04746835]),
-                ([0.06329114, 0.05617978], [-0.04746835, -0.04213483]),
-                ([0.06329114, -0.06329114], [-0.04746835, -0.04746835]),
+                ([-0.06329114, -0.06329114], [0.04746835, -0.04746835]),
+                ([0.06329114, 0.05617978], [0.04746835, 0.04213483]),
+                ([0.06329114, -0.06329114], [0.04746835, 0.04746835]),
             ],
             [1, 2, 1],
         ),