Fix layers 3 & above overlapping the axis lines

fixes #798

Author: has2k1

doc/changelog.qmd

@@ -15,6 +15,10 @@ title: Changelog
 - [](:class:`~plotnine.geom_text`) has gained new aesthetics
   `fontvariant` and `fontstretch`.
 
+### Bug Fixes
+
+- Fix layers 3 and above not to overlap the axis lines if there are any
+  ({{< issue 798 >}}).
 
 ## v0.13.6
 (2024-05-09)

plotnine/themes/themeable.py

@@ -893,8 +893,13 @@ class axis_line_x(themeable):
 
     def apply_ax(self, ax: Axes):
         super().apply_ax(ax)
+        properties = self.properties
+        # MPL has a default zorder of 2.5 for spines
+        # so layers 3+ would be drawn on top of the spines
+        if "zorder" not in properties:
+            properties["zorder"] = 10000
         ax.spines["top"].set_visible(False)
-        ax.spines["bottom"].set(**self.properties)
+        ax.spines["bottom"].set(**properties)
 
     def blank_ax(self, ax: Axes):
         super().blank_ax(ax)
@@ -916,8 +921,13 @@ class axis_line_y(themeable):
 
     def apply_ax(self, ax: Axes):
         super().apply_ax(ax)
+        properties = self.properties
+        # MPL has a default zorder of 2.5 for spines
+        # so layers 3+ would be drawn on top of the spines
+        if "zorder" not in properties:
+            properties["zorder"] = 10000
         ax.spines["right"].set_visible(False)
-        ax.spines["left"].set(**self.properties)
+        ax.spines["left"].set(**properties)
 
     def blank_ax(self, ax: Axes):
         super().blank_ax(ax)