Improve formatting of imshow() cursor data when a colorbar exists.

anntzer · Stephen-Chilcote · commit 97bec728cb03 · 2018-12-11T12:58:15.000-05:00
When a colorbar exists, use its formatter to format cursor data.
For example, after
```
imshow([[10000, 10001]]); colorbar()
```
currently the cursor data on either pixel is rendered as 1e4, but after
this patch it becomes 0.0+1e4 / 1.0+1e4, or 10000.0 / 10001.0 if
`rcParams["axes.formatter.useoffset"]` is set to False.  (Even though
the version with the offset text may not be the most esthetic, it's
clearly more informative than the current behavior...)

It would be nice if this worked even for ScalarMappables that don't
have a colorbar; this may include extracting the Formatter selection
code out of the colorbar code into something generally applicable to
ScalarMappables, or just generating a hidden colorbar "on-the-fly" if
needed just for the purpose of getting its Formatter.
diff --git a/doc/users/next_whats_new/2018-10-10-AL.rst b/doc/users/next_whats_new/2018-10-10-AL.rst
@@ -0,0 +1,9 @@
+Improved formatting of image values under cursor when a colorbar is present
+```````````````````````````````````````````````````````````````````````````
+
+When a colorbar is present, its formatter is now used to format the image
+values under the mouse cursor in the status bar.  For example, for an image
+displaying the values 10,000 and 10,001, the statusbar will now (using default
+settings) display the values as ``0.0+1e4`` and ``1.0+1e4`` (or ``10000.0``
+and ``10001.0`` if the offset-text is disabled on the colorbar), whereas both
+values were previously displayed as ``1e+04``.
diff --git a/lib/matplotlib/artist.py b/lib/matplotlib/artist.py
@@ -2,6 +2,7 @@
 from functools import wraps
 import inspect
 import logging
+from numbers import Number
 import re
 import warnings
 
@@ -1165,8 +1166,8 @@ def format_cursor_data(self, data):
             data[0]
         except (TypeError, IndexError):
             data = [data]
-        data_str = ', '.join('{:0.3g}'.format(item) for item in data if
-                   isinstance(item, (np.floating, np.integer, int, float)))
+        data_str = ', '.join('{:0.3g}'.format(item) for item in data
+                             if isinstance(item, Number))
         return "[" + data_str + "]"
 
     @property
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -302,11 +302,17 @@ def local_over_kwdict(local_var, kwargs, *keys):
 
 
 def strip_math(s):
-    """remove latex formatting from mathtext"""
-    remove = (r'\mathdefault', r'\rm', r'\cal', r'\tt', r'\it', '\\', '{', '}')
-    s = s[1:-1]
-    for r in remove:
-        s = s.replace(r, '')
+    """
+    Remove latex formatting from mathtext.
+
+    Only handles fully math and fully non-math strings.
+    """
+    if len(s) >= 2 and s[0] == s[-1] == "$":
+        s = s[1:-1]
+        remove = [
+            r'\mathdefault', r'\rm', r'\cal', r'\tt', r'\it', '\\', '{', '}']
+        for r in remove:
+            s = s.replace(r, '')
     return s
 
 
diff --git a/lib/matplotlib/image.py b/lib/matplotlib/image.py
@@ -906,6 +906,15 @@ def get_cursor_data(self, event):
         else:
             return arr[i, j]
 
+    def format_cursor_data(self, data):
+        if self.colorbar:
+            return ("["
+                    + cbook.strip_math(self.colorbar.formatter(data))
+                    + cbook.strip_math(self.colorbar.formatter.get_offset())
+                    + "]")
+        else:
+            return super().format_cursor_data(data)
+
 
 class NonUniformImage(AxesImage):
     def __init__(self, ax, *, interpolation='nearest', **kwargs):
diff --git a/lib/matplotlib/tests/test_image.py b/lib/matplotlib/tests/test_image.py
@@ -262,6 +262,24 @@ def test_cursor_data():
     assert im.get_cursor_data(event) is None
 
 
+def test_format_cursor_data():
+    from matplotlib.backend_bases import MouseEvent
+
+    fig, ax = plt.subplots()
+    im = ax.imshow([[10000, 10001]])
+
+    xdisp, ydisp = ax.transData.transform_point([0, 0])
+    event = MouseEvent('motion_notify_event', fig.canvas, xdisp, ydisp)
+    assert im.get_cursor_data(event) == 10000
+    assert im.format_cursor_data(im.get_cursor_data(event)) == "[1e+04]"
+
+    fig.colorbar(im)
+    fig.canvas.draw()  # This is necessary to set up the colorbar formatter.
+
+    assert im.get_cursor_data(event) == 10000
+    assert im.format_cursor_data(im.get_cursor_data(event)) == "[0.0+1e4]"
+
+
 @image_comparison(baseline_images=['image_clip'], style='mpl20')
 def test_image_clip():
     d = [[1, 2], [3, 4]]
