Add an 'auto' option to label rotation.

This option enables the automatic rotation of polar tick labels.
matplotlib · tacaswell · Sep 26, 2017 · Aug 4, 2017 · Aug 4, 2017 · Aug 4, 2017
commit 228ee536f81ac92d69caef1a0b40669a5ea96ad1
diff --git a/doc/users/whats_new.rst b/doc/users/whats_new.rst
@@ -62,10 +62,13 @@ negative values are simply used as labels, and the real radius is shifted by
 the configured minimum. This release also allows negative radii to be used for
 grids and ticks, which were previously silently ignored.
 
-For plots of a partial circle, radial ticks and tick labels have been modified
-to be parallel to the circular grid line. Angular ticks have been modified to
-be parallel to the grid line and the labels are now perpendicular to the grid
-line (i.e., parallel to the outer boundary.)
+Radial ticks have be modified to be parallel to the circular grid line. Angular
+ticks will be modified to be parallel to the grid line. It may also be useful
+to rotate tick labels to match the boundary. Calling
+``ax.tick_params(rotation='auto')`` will enable this new behavior. Radial tick
+labels will be modified to be parallel to the circular grid line. Angular tick
+labels will be perpendicular to the grid line (i.e., parallel to the outer
+boundary.)
 
 
 Merge JSAnimation

diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
@@ -140,7 +140,7 @@ def __init__(self, axes, loc, label,
             labelsize = rcParams['%s.labelsize' % name]
         self._labelsize = labelsize
 
-        self._labelrotation = labelrotation
+        self._set_labelrotation(labelrotation)
 
         if zorder is None:
             if major:
@@ -167,6 +167,20 @@ def __init__(self, axes, loc, label,
 
         self.update_position(loc)
 
+    def _set_labelrotation(self, labelrotation):
+        if isinstance(labelrotation, six.string_types):
+            mode = labelrotation
+            angle = 0
+        elif isinstance(labelrotation, (tuple, list)):
+            mode, angle = labelrotation
+        else:
+            mode = 'default'
+            angle = labelrotation
+        if mode not in ('auto', 'default'):
+            raise ValueError("Label rotation mode must be 'default' or "
+                             "'auto', not '{}'.".format(mode))
+        self._labelrotation = (mode, angle)
+
     def apply_tickdir(self, tickdir):
         """
         Calculate self._pad and self._tickmarkers
@@ -331,8 +345,14 @@ def _apply_params(self, **kw):
             self.tick2line.set(**tick_kw)
             for k, v in six.iteritems(tick_kw):
                 setattr(self, '_' + k, v)
+
+        if 'labelrotation' in kw:
+            self._set_labelrotation(kw.pop('labelrotation'))
+            self.label1.set(rotation=self._labelrotation[1])
+            self.label2.set(rotation=self._labelrotation[1])
+
         label_list = [k for k in six.iteritems(kw)
-                      if k[0] in ['labelsize', 'labelcolor', 'labelrotation']]
+                      if k[0] in ['labelsize', 'labelcolor']]
         if label_list:
             label_kw = {k[5:]: v for k, v in label_list}
             self.label1.set(**label_kw)

diff --git a/lib/matplotlib/projections/polar.py b/lib/matplotlib/projections/polar.py
@@ -1,6 +1,8 @@
 from __future__ import (absolute_import, division, print_function,
                         unicode_literals)
 
+import six
+
 from collections import OrderedDict
 
 import numpy as np
@@ -251,9 +253,9 @@ class ThetaTick(maxis.XTick):
     tick location. This results in ticks that are correctly perpendicular to
     the arc spine.
 
-    Labels are also rotated to be parallel to the spine. The label padding is
-    also applied here since it's not possible to use a generic axes transform
-    to produce tick-specific padding.
+    When 'auto' rotation is enabled, labels are also rotated to be parallel to
+    the spine. The label padding is also applied here since it's not possible
+    to use a generic axes transform to produce tick-specific padding.
     """
     def __init__(self, axes, *args, **kwargs):
         self._text1_translate = mtransforms.ScaledTranslation(
@@ -322,14 +324,15 @@ def update_position(self, loc):
                 trans = self.tick2line._marker._transform
             self.tick2line._marker._transform = trans
 
-        if not _is_full_circle_deg(axes.get_thetamin(), axes.get_thetamax()):
+        mode, user_angle = self._labelrotation
+        if mode == 'default':
+            angle = 0
+        else:
             if angle > np.pi / 2:
                 angle -= np.pi
             elif angle < -np.pi / 2:
                 angle += np.pi
-        else:
-            angle = 0
-        angle = np.rad2deg(angle) + self._labelrotation
+        angle = np.rad2deg(angle) + user_angle
         if self.label1On:
             self.label1.set_rotation(angle)
         if self.label2On:
@@ -488,8 +491,8 @@ class RadialTick(maxis.YTick):
     This subclass of `YTick` provides radial ticks with some small modification
     to their re-positioning such that ticks are rotated based on axes limits.
     This results in ticks that are correctly perpendicular to the spine. Labels
-    are also rotated to be perpendicular to the spine, but only for wedges, to
-    preserve backwards compatibility.
+    are also rotated to be perpendicular to the spine, when 'auto' rotation is
+    enabled.
     """
     def _get_text1(self):
         t = super(RadialTick, self)._get_text1()
@@ -524,9 +527,14 @@ def update_position(self, loc):
         full = _is_full_circle_deg(thetamin, thetamax)
 
         if full:
-            angle = axes.get_rlabel_position()
+            angle = axes.get_rlabel_position() * direction + offset - 90
             tick_angle = 0
-            text_angle = 0
+            if angle > 90:
+                text_angle = angle - 180
+            elif angle < -90:
+                text_angle = angle + 180
+            else:
+                text_angle = angle
         else:
             angle = thetamin * direction + offset - 90
             if direction > 0:
@@ -539,7 +547,11 @@ def update_position(self, loc):
                 text_angle = angle + 180
             else:
                 text_angle = angle
-        text_angle += self._labelrotation
+        mode, user_angle = self._labelrotation
+        if mode == 'auto':
+            text_angle += user_angle
+        else:
+            text_angle = user_angle
         if self.label1On:
             if full:
                 ha = 'left'
@@ -583,7 +595,11 @@ def update_position(self, loc):
                 text_angle = angle + 180
             else:
                 text_angle = angle
-        text_angle += self._labelrotation
+        mode, user_angle = self._labelrotation
+        if mode == 'auto':
+            text_angle += user_angle
+        else:
+            text_angle = user_angle
         if self.label2On:
             ha, va = self._determine_anchor(angle, False)
             self.label2.set_ha(ha)

diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -668,6 +668,7 @@ def test_polar_rlabel_position():
     fig = plt.figure()
     ax = fig.add_subplot(111, projection='polar')
     ax.set_rlabel_position(315)
+    ax.tick_params(rotation='auto')
 
 
 @image_comparison(baseline_images=['polar_theta_wedge'], style='default',
@@ -692,8 +693,9 @@ def test_polar_theta_limits():
                 ax.set_thetamin(start)
                 ax.set_thetamax(end)
                 ax.tick_params(tick1On=True, tick2On=True,
-                               direction=DIRECTIONS[i % len(DIRECTIONS)])
-                ax.yaxis.set_tick_params(label2On=True)
+                               direction=DIRECTIONS[i % len(DIRECTIONS)],
+                               rotation='auto')
+                ax.yaxis.set_tick_params(label2On=True, rotation='auto')
             else:
                 ax.set_visible(False)