Merge pull request matplotlib#28968 from kyracho/positioning_for_rotated_labels

Implement xtick and ytick rotation modes

Author: tacaswell

doc/users/next_whats_new/xtick_ytick_rotation_modes.rst

@@ -0,0 +1,28 @@
+``xtick`` and ``ytick`` rotation modes
+--------------------------------------
+
+A new feature has been added for handling rotation of xtick and ytick
+labels more intuitively. The new `rotation modes <matplotlib.text.Text.set_rotation_mode>`
+"xtick" and "ytick" automatically adjust the alignment of rotated tick labels,
+so that the text points towards their anchor point, i.e. ticks.  This works for
+all four sides of the plot (bottom, top, left, right), reducing the need for
+manual adjustments when rotating labels.
+
+.. plot::
+    :include-source: true
+    :alt: Example of rotated xtick and ytick labels.
+
+    import matplotlib.pyplot as plt
+
+    fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(7, 3.5), layout='constrained')
+
+    pos = range(5)
+    labels = ['label'] * 5
+    ax1.set_xticks(pos, labels, rotation=-45, rotation_mode='xtick')
+    ax1.set_yticks(pos, labels, rotation=45, rotation_mode='ytick')
+    ax2.xaxis.tick_top()
+    ax2.set_xticks(pos, labels, rotation=-45, rotation_mode='xtick')
+    ax2.yaxis.tick_right()
+    ax2.set_yticks(pos, labels, rotation=45, rotation_mode='ytick')
+
+    plt.show()

galleries/examples/images_contours_and_fields/image_annotated_heatmap.py

@@ -64,7 +64,7 @@
 
 # Show all ticks and label them with the respective list entries
 ax.set_xticks(range(len(farmers)), labels=farmers,
-              rotation=45, ha="right", rotation_mode="anchor")
+              rotation=45, rotation_mode="xtick")
 ax.set_yticks(range(len(vegetables)), labels=vegetables)
 
 # Loop over data dimensions and create text annotations.
@@ -135,7 +135,7 @@ def heatmap(data, row_labels, col_labels, ax=None,
 
     # Show all ticks and label them with the respective list entries.
     ax.set_xticks(range(data.shape[1]), labels=col_labels,
-                  rotation=-30, ha="right", rotation_mode="anchor")
+                  rotation=-30, rotation_mode="xtick")
     ax.set_yticks(range(data.shape[0]), labels=row_labels)
 
     # Let the horizontal axes labeling appear on top.

galleries/examples/subplots_axes_and_figures/align_labels_demo.py

@@ -26,7 +26,8 @@
 ax.plot(np.arange(1., 0., -0.1) * 2000., np.arange(1., 0., -0.1))
 ax.set_title('Title0 1')
 ax.xaxis.tick_top()
-ax.tick_params(axis='x', rotation=55)
+ax.set_xticks(ax.get_xticks())
+ax.tick_params(axis='x', rotation=55, rotation_mode='xtick')
 
 
 for i in range(2):
@@ -35,7 +36,8 @@
     ax.set_ylabel('YLabel1 %d' % i)
     ax.set_xlabel('XLabel1 %d' % i)
     if i == 0:
-        ax.tick_params(axis='x', rotation=55)
+        ax.set_xticks(ax.get_xticks())
+        ax.tick_params(axis='x', rotation=55, rotation_mode='xtick')
 
 fig.align_labels()  # same as fig.align_xlabels(); fig.align_ylabels()
 fig.align_titles()

lib/matplotlib/axis.py

@@ -134,7 +134,7 @@ def __init__(
             #   grid(color=(1, 1, 1, 0.5), alpha=rcParams['grid.alpha'])
             # so the that the rcParams default would override color alpha.
             grid_alpha = mpl.rcParams["grid.alpha"]
-        grid_kw = {k[5:]: v for k, v in kwargs.items()}
+        grid_kw = {k[5:]: v for k, v in kwargs.items() if k != "rotation_mode"}
 
         self.tick1line = mlines.Line2D(
             [], [],
@@ -1050,7 +1050,7 @@ def _translate_tick_params(cls, kw, reverse=False):
             'tick1On', 'tick2On', 'label1On', 'label2On',
             'length', 'direction', 'left', 'bottom', 'right', 'top',
             'labelleft', 'labelbottom', 'labelright', 'labeltop',
-            'labelrotation',
+            'labelrotation', 'rotation_mode',
             *_gridline_param_names]
 
         keymap = {

lib/matplotlib/tests/baseline_images/test_text/xtick_rotation_mode.png

@@ -1135,3 +1135,58 @@ def test_font_wrap():
     plt.text(3, 4, t, family='monospace', ha='right', wrap=True)
     plt.text(-1, 0, t, fontsize=14, style='italic', ha='left', rotation=-15,
              wrap=True)
+
+
+def test_ha_for_angle():
+    text_instance = Text()
+    angles = np.arange(0, 360.1, 0.1)
+    for angle in angles:
+        alignment = text_instance._ha_for_angle(angle)
+        assert alignment in ['center', 'left', 'right']
+
+
+def test_va_for_angle():
+    text_instance = Text()
+    angles = np.arange(0, 360.1, 0.1)
+    for angle in angles:
+        alignment = text_instance._va_for_angle(angle)
+        assert alignment in ['center', 'top', 'baseline']
+
+
+@image_comparison(baseline_images=['xtick_rotation_mode'],
+                  remove_text=False, extensions=['png'], style='mpl20')
+def test_xtick_rotation_mode():
+    fig, ax = plt.subplots(figsize=(12, 1))
+    ax.set_yticks([])
+    ax2 = ax.twiny()
+
+    ax.set_xticks(range(37), ['foo'] * 37, rotation_mode="xtick")
+    ax2.set_xticks(range(37), ['foo'] * 37, rotation_mode="xtick")
+
+    angles = np.linspace(0, 360, 37)
+
+    for tick, angle in zip(ax.get_xticklabels(), angles):
+        tick.set_rotation(angle)
+    for tick, angle in zip(ax2.get_xticklabels(), angles):
+        tick.set_rotation(angle)
+
+    plt.subplots_adjust(left=0.01, right=0.99, top=.6, bottom=.4)
+
+
+@image_comparison(baseline_images=['ytick_rotation_mode'],
+                  remove_text=False, extensions=['png'], style='mpl20')
+def test_ytick_rotation_mode():
+    fig, ax = plt.subplots(figsize=(1, 12))
+    ax.set_xticks([])
+    ax2 = ax.twinx()
+
+    ax.set_yticks(range(37), ['foo'] * 37, rotation_mode="ytick")
+    ax2.set_yticks(range(37), ['foo'] * 37, rotation_mode='ytick')
+
+    angles = np.linspace(0, 360, 37)
+    for tick, angle in zip(ax.get_yticklabels(), angles):
+        tick.set_rotation(angle)
+    for tick, angle in zip(ax2.get_yticklabels(), angles):
+        tick.set_rotation(angle)
+
+    plt.subplots_adjust(left=0.4, right=0.6, top=.99, bottom=.01)

lib/matplotlib/tests/baseline_images/test_text/ytick_rotation_mode.png

@@ -300,16 +300,19 @@ def set_rotation_mode(self, m):
 
         Parameters
         ----------
-        m : {None, 'default', 'anchor'}
+        m : {None, 'default', 'anchor', 'xtick', 'ytick'}
             If ``"default"``, the text will be first rotated, then aligned according
             to their horizontal and vertical alignments.  If ``"anchor"``, then
-            alignment occurs before rotation. Passing ``None`` will set the rotation
-            mode to ``"default"``.
+            alignment occurs before rotation. "xtick" and "ytick" adjust the
+            horizontal/vertical alignment so that the text is visually pointing
+            towards its anchor point. This is primarily used for rotated tick
+            labels and positions them nicely towards their ticks. Passing
+            ``None`` will set the rotation mode to ``"default"``.
         """
         if m is None:
             m = "default"
         else:
-            _api.check_in_list(("anchor", "default"), rotation_mode=m)
+            _api.check_in_list(("anchor", "default", "xtick", "ytick"), rotation_mode=m)
         self._rotation_mode = m
         self.stale = True
 
@@ -453,6 +456,11 @@ def _get_layout(self, renderer):
 
         rotation_mode = self.get_rotation_mode()
         if rotation_mode != "anchor":
+            angle = self.get_rotation()
+            if rotation_mode == 'xtick':
+                halign = self._ha_for_angle(angle)
+            elif rotation_mode == 'ytick':
+                valign = self._va_for_angle(angle)
             # compute the text location in display coords and the offsets
             # necessary to align the bbox with that location
             if halign == 'center':
@@ -1376,6 +1384,32 @@ def set_fontname(self, fontname):
         """
         self.set_fontfamily(fontname)
 
+    def _ha_for_angle(self, angle):
+        """
+        Determines horizontal alignment ('ha') for rotation_mode "xtick" based on
+        the angle of rotation in degrees and the vertical alignment.
+        """
+        anchor_at_bottom = self.get_verticalalignment() == 'bottom'
+        if (angle <= 10 or 85 <= angle <= 95 or 350 <= angle or
+                170 <= angle <= 190 or 265 <= angle <= 275):
+            return 'center'
+        elif 10 < angle < 85 or 190 < angle < 265:
+            return 'left' if anchor_at_bottom else 'right'
+        return 'right' if anchor_at_bottom else 'left'
+
+    def _va_for_angle(self, angle):
+        """
+        Determines vertical alignment ('va') for rotation_mode "ytick" based on
+        the angle of rotation in degrees and the horizontal alignment.
+        """
+        anchor_at_left = self.get_horizontalalignment() == 'left'
+        if (angle <= 10 or 350 <= angle or 170 <= angle <= 190
+                or 80 <= angle <= 100 or 260 <= angle <= 280):
+            return 'center'
+        elif 190 < angle < 260 or 10 < angle < 80:
+            return 'baseline' if anchor_at_left else 'top'
+        return 'top' if anchor_at_left else 'baseline'
+
 
 class OffsetFrom:
     """Callable helper class for working with `Annotation`."""

lib/matplotlib/tests/test_text.py

@@ -106,6 +106,8 @@ class Text(Artist):
     def set_fontname(self, fontname: str | Iterable[str]) -> None: ...
     def get_antialiased(self) -> bool: ...
     def set_antialiased(self, antialiased: bool) -> None: ...
+    def _ha_for_angle(self, angle: Any) -> Literal['center', 'right', 'left'] | None: ...
+    def _va_for_angle(self, angle: Any) -> Literal['center', 'top', 'baseline'] | None: ...
 
 class OffsetFrom:
     def __init__(