Make polar stereograhic grid use Matplotlib's 'grid.alpha'

Signed-off-by: Håkon Wiik Ånes <hwaanes@gmail.com>

CHANGELOG.rst

@@ -24,6 +24,8 @@ Removed
 
 Fixed
 -----
+- Transparency of polar stereographic grid lines can now be controlled by Matplotlib's
+  ``grid.alpha``, just like the azimuth grid lines.
 
 2023-03-14 - version 0.11.1
 ===========================

orix/plot/stereographic_plot.py

@@ -746,6 +746,7 @@ def _polar_grid(self, resolution: Optional[float] = None):
             label=label,
             edgecolors=kwargs["ec"],
             facecolors=kwargs["fc"],
+            alpha=kwargs["alpha"],
         )
         has_collection, index = self._has_collection(label, self.collections)
         if has_collection:

orix/tests/plot/test_stereographic_plot.py

@@ -102,10 +102,15 @@ def test_grids(self):
         assert ax._azimuth_resolution == azimuth_res
         assert ax._polar_resolution == polar_res
 
-        ax.stereographic_grid(azimuth_resolution=30, polar_resolution=45)
+        alpha = 0.5
+        with plt.rc_context({"grid.alpha": alpha}):
+            ax.stereographic_grid(azimuth_resolution=30, polar_resolution=45)
         assert ax._azimuth_resolution == 30
         assert ax._polar_resolution == 45
 
+        assert len(ax.collections) == 2
+        assert all([coll.get_alpha() for coll in ax.collections])
+
         plt.close("all")
 
     def test_set_labels(self):