ENH: Support minor grid in Axes3D

EncryptedDoom · EncryptedDoom · commit 8ddadfcaffc1 · 2026-04-19T14:51:12.000+05:30
`ax.grid(which='minor')` was silently ignored on Axes3D.
This commit adds full minor grid support by extending grid(),
adding draw_minor_grid() to axis3d.py, and adding a test.
diff --git a/lib/mpl_toolkits/mplot3d/axes3d.py b/lib/mpl_toolkits/mplot3d/axes3d.py
@@ -501,6 +501,9 @@ def draw(self, renderer):
             # Then gridlines
             for axis in self._axis_map.values():
                 axis.draw_grid(renderer)
+            # Then minor gridlines
+            for axis in self._axis_map.values():
+                axis.draw_minor_grid(renderer)
             # Then axes, labels, text, and ticks
             for axis in self._axis_map.values():
                 axis.draw(renderer)
@@ -1562,6 +1565,9 @@ def clear(self):
         self._view_margin = 1/48  # default value to match mpl3.8
         self.autoscale_view()
 
+        self._draw_minor_grid = False
+        self._minor_grid_kwargs = {}
+        self.grid(mpl.rcParams['axes3d.grid'])
         self.grid(mpl.rcParams['axes3d.grid'])
 
     def _button_press(self, event):
@@ -2055,21 +2061,31 @@ def get_zlabel(self):
     get_frame_on = None
     set_frame_on = None
 
-    def grid(self, visible=True, **kwargs):
-        """
-        Set / unset 3D grid.
-
-        .. note::
-
-            Currently, this function does not behave the same as
-            `.axes.Axes.grid`, but it is intended to eventually support that
-            behavior.
-        """
-        # TODO: Operate on each axes separately
-        if len(kwargs):
-            visible = True
-        self._draw_grid = visible
-        self.stale = True
+    def grid(self, visible=True, which='major', axis='both', **kwargs):
+       """
+       Set / unset 3D grid.
+
+       .. note::
+           Currently, this function does not behave the same as
+           :meth:`matplotlib.axes.Axes.grid`, but it is intended to
+           eventually support that behavior.
+
+       Parameters
+       ----------
+       visible : bool
+       which : {'major', 'minor', 'both'}
+       axis : {'both', 'x', 'y', 'z'}
+       **kwargs : Line properties forwarded to the grid lines.
+       """
+       if len(kwargs):
+           visible = True
+       if which in ('major', 'both'):
+           self._draw_grid = bool(visible)
+           self._major_grid_kwargs = kwargs
+       if which in ('minor', 'both'):
+           self._draw_minor_grid = bool(visible)
+           self._minor_grid_kwargs = kwargs
+       self.stale = True
 
     def tick_params(self, axis='both', **kwargs):
         """
diff --git a/lib/mpl_toolkits/mplot3d/axis3d.py b/lib/mpl_toolkits/mplot3d/axis3d.py
@@ -160,6 +160,8 @@ def _init3d(self):
         self.axes._set_artist_props(self.pane)
         self.gridlines = art3d.Line3DCollection([])
         self.axes._set_artist_props(self.gridlines)
+        self.minor_gridlines = art3d.Line3DCollection([])
+        self.axes._set_artist_props(self.minor_gridlines)
         self.axes._set_artist_props(self.label)
         self.axes._set_artist_props(self.offsetText)
         # Need to be able to place the label at the correct location
@@ -678,6 +680,59 @@ def draw_grid(self, renderer):
 
         renderer.close_group('grid3d')
 
+    @artist.allow_rasterization
+    def draw_minor_grid(self, renderer):
+        if not getattr(self.axes, '_draw_minor_grid', False):
+            return
+
+        renderer.open_group("minor_grid3d", gid=self.get_gid())
+
+        minor_locs = self.get_minorticklocs()
+        if len(minor_locs):
+            info = self._axinfo
+            index = info["i"]
+
+            mins, maxs, tc, highs = self._get_coord_info()
+            xlim, ylim, zlim = (self.axes.get_xbound(),
+                                self.axes.get_ybound(),
+                                self.axes.get_zbound())
+            data_mins = np.array([xlim[0], ylim[0], zlim[0]])
+            data_maxs = np.array([xlim[1], ylim[1], zlim[1]])
+            minmax = np.where(highs, data_maxs, data_mins)
+            maxmin = np.where(~highs, data_maxs, data_mins)
+
+            # Filter to ticks within view limits
+            vmin, vmax = self.get_view_interval()
+            minor_locs = [t for t in minor_locs if vmin <= t <= vmax]
+
+            if len(minor_locs):
+                xyz0 = np.tile(minmax, (len(minor_locs), 1))
+                xyz0[:, index] = minor_locs
+
+                lines = np.stack([xyz0, xyz0, xyz0], axis=1)
+                lines[:, 0, index - 2] = maxmin[index - 2]
+                lines[:, 2, index - 1] = maxmin[index - 1]
+
+                self.minor_gridlines.set_segments(lines)
+
+                # Default minor style: thinner and more transparent than major
+                gridinfo = info['grid']
+                minor_kw = {
+                    'color':     gridinfo['color'],
+                    'linewidth': gridinfo['linewidth'] * 0.5,
+                    'linestyle': gridinfo['linestyle'],
+                }
+                # Apply any user overrides from ax.grid(which='minor', ...)
+                minor_kw.update(getattr(self.axes, '_minor_grid_kwargs', {}))
+
+                self.minor_gridlines.set_color(minor_kw['color'])
+                self.minor_gridlines.set_linewidth(minor_kw['linewidth'])
+                self.minor_gridlines.set_linestyle(minor_kw['linestyle'])
+                self.minor_gridlines.do_3d_projection()
+                self.minor_gridlines.draw(renderer)
+
+        renderer.close_group('minor_grid3d')
+
     # TODO: Get this to work (more) properly when mplot3d supports the
     #       transforms framework.
     def get_tightbbox(self, renderer=None, *, for_layout_only=False):
diff --git a/lib/mpl_toolkits/mplot3d/tests/test_axes3d.py b/lib/mpl_toolkits/mplot3d/tests/test_axes3d.py
@@ -50,6 +50,25 @@ def test_grid_off():
     ax.grid(False)
 
 
+def test_minor_grid_3d():
+    fig = plt.figure()
+    ax = fig.add_subplot(111, projection='3d')
+    ax.scatter([1, 2, 3], [1, 2, 3], [1, 2, 3])
+
+    # Minor grid off by default
+    assert not ax._draw_minor_grid
+
+    # Enabling sets the flag and stores kwargs
+    ax.grid(which='minor', color='lightgrey', linewidth=0.3)
+    assert ax._draw_minor_grid
+    assert ax._minor_grid_kwargs['linewidth'] == 0.3
+
+    # Major grid unaffected
+    assert ax._draw_grid
+
+    plt.close(fig)
+
+
 @mpl3d_image_comparison(['invisible_ticks_axis.png'], style='mpl20')
 def test_invisible_ticks_axis():
     fig = plt.figure()
