Merge pull request matplotlib#23111 from anntzer/gsg

Fix _g_sig_digits for value<0 and delta=0.

Author: timhoffm

lib/matplotlib/cbook/__init__.py

@@ -2158,7 +2158,7 @@ def _g_sig_digits(value, delta):
     if delta == 0:
         # delta = 0 may occur when trying to format values over a tiny range;
         # in that case, replace it by the distance to the closest float.
-        delta = np.spacing(value)
+        delta = abs(np.spacing(value))
     # If e.g. value = 45.67 and delta = 0.02, then we want to round to 2 digits
     # after the decimal point (floor(log10(0.02)) = -2); 45.67 contributes 2
     # digits before the decimal point (floor(log10(45.67)) + 1 = 2): the total

lib/matplotlib/tests/test_image.py

@@ -342,6 +342,7 @@ def test_cursor_data():
         ([[.123, .987]], "[0.123]"),
         ([[np.nan, 1, 2]], "[]"),
         ([[1, 1+1e-15]], "[1.0000000000000000]"),
+        ([[-1, -1]], "[-1.0000000000000000]"),
     ])
 def test_format_cursor_data(data, text):
     from matplotlib.backend_bases import MouseEvent