Only allow rotations on equal-aspect Axes

dstansby · dstansby · commit 7645b29542dc · 2021-06-27T15:31:16.000+01:00
diff --git a/doc/users/next_whats_new/selector_rotate.rst b/doc/users/next_whats_new/selector_rotate.rst
@@ -2,6 +2,7 @@ Rotating selectors
 ------------------
 
 The `~matplotlib.widgets.RectangleSelector` and
-`~matplotlib.widgets.EllipseSelector` can now be rotated by pressing the 'r' key,
-and dragging one of their control points. The rotation is done about the first
-vertex placed when drawing the selector.
+`~matplotlib.widgets.EllipseSelector` can now be rotated by pressing the 'r'
+key, and dragging one of their control points. This is currently only
+implemented for equal-aspect axes. The rotation is done about the
+first vertex placed when drawing the selector.
diff --git a/lib/matplotlib/tests/test_widgets.py b/lib/matplotlib/tests/test_widgets.py
@@ -226,6 +226,38 @@ def onselect(epress, erelease):
     assert tool.corners == ((100, 112, 100, 88), (100, 109, 125, 116))
 
 
+@pytest.mark.parametrize('selector_class', [widgets.RectangleSelector,
+                                            widgets.EllipseSelector])
+def test_rotate_warning(selector_class):
+    # Check that a warning is raised when trying to rotate on a
+    # non-equal aspect Axes.
+    ax = get_ax()
+
+    def onselect(epress, erelease):
+        pass
+
+    tool = selector_class(ax, onselect=onselect, interactive=True)
+    ax.set_aspect(2)
+
+    # Draw rectangle
+    do_event(tool, 'press', xdata=100, ydata=100)
+    do_event(tool, 'onmove', xdata=130, ydata=140)
+    do_event(tool, 'release', xdata=130, ydata=140)
+    old_corners = tool.corners
+
+    # Try to rotate
+    do_event(tool, 'on_key_press', key='r')
+    do_event(tool, 'press', xdata=130, ydata=140)
+    # Check warning is raised
+    with pytest.warns(UserWarning, match='Rotation is only implemented for '
+                                         'equal-aspect Axes.'):
+        do_event(tool, 'onmove', xdata=100, ydata=150)
+    do_event(tool, 'release', xdata=100, ydata=200)
+    do_event(tool, 'on_key_release', key='r')
+    # Check that corners haven't moved
+    assert tool.corners == old_corners
+
+
 def check_span(*args, **kwargs):
     ax = get_ax()
 
diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
@@ -12,6 +12,7 @@
 from contextlib import ExitStack
 import copy
 from numbers import Integral, Number
+import warnings
 
 import numpy as np
 
@@ -2269,7 +2270,7 @@ def onselect(eclick: MouseEvent, erelease: MouseEvent)
             - "center": Make the initial point the center of the shape,
               default: "ctrl".
             - "rotate": Rotate the shape around its corner,
-              default: "r".
+              default: "r". This currently only works for equal-aspect axes.
 
             "square" and "center" can be combined.
 
@@ -2452,11 +2453,15 @@ def _onmove(self, event):
 
         # rotate existing shape
         if 'rotate' in self.state:
-            rotation_new = np.arctan2(ymove - y0,
-                                      xmove - x0)
-            rotation_old = np.arctan2(self._prev_ymove - y0,
-                                      self._prev_xmove - x0)
-            rotation += rotation_new - rotation_old
+            if self.ax.get_aspect() == 1:
+                rotation_new = np.arctan2(ymove - y0,
+                                          xmove - x0)
+                rotation_old = np.arctan2(self._prev_ymove - y0,
+                                          self._prev_xmove - x0)
+                rotation += rotation_new - rotation_old
+            else:
+                warnings.warn('Rotation is only implemented for '
+                              'equal-aspect Axes.')
 
         # move existing shape
         elif ('move' in self.state or
