Add high contrast functionality to timestamp

metpy/plots/_util.py

@@ -6,6 +6,7 @@
 from datetime import datetime
 import posixpath
 
+from matplotlib import patheffects
 from matplotlib.collections import LineCollection
 from matplotlib.pyplot import imread
 import numpy as np
@@ -14,7 +15,7 @@
 from ..units import concatenate
 
 
-def add_timestamp(ax, time=None, x=0.99, y=-0.04, ha='right', **kwargs):
+def add_timestamp(ax, time=None, x=0.99, y=-0.04, ha='right', high_contrast=False, **kwargs):
     """Add a timestamp at plot creation time.
 
     Adds an ISO format timestamp with the time of plot creation to the plot.
@@ -31,17 +32,31 @@ def add_timestamp(ax, time=None, x=0.99, y=-0.04, ha='right', **kwargs):
         Relative y position on the axes of the timestamp
     ha : str
         Horizontal alignment of the time stamp string
+    high_contrast : bool
+        Outline text for increased contrast
 
     Returns
     -------
     `matplotlib.text.Text`
         The `matplotlib.text.Text` instance created
 
     """
+    if high_contrast:
+        text_args = {'color': 'white'}
+    else:
+        text_args = {}
+    text_args.update(**kwargs)
     if not time:
         time = datetime.utcnow()
     timestr = datetime.strftime(time, 'Created: %Y-%m-%dT%H:%M:%SZ')
-    return ax.text(x, y, timestr, ha=ha, transform=ax.transAxes, **kwargs)
+    text = ax.text(x, y, timestr, ha=ha, transform=ax.transAxes, **text_args)
+
+    if high_contrast:
+        # Make the text stand out even better using matplotlib's path effects
+        outline_effect = [patheffects.withStroke(linewidth=2, foreground='black')]
+        text.set_path_effects(outline_effect)
+
+    return text
 
 
 def _add_logo(fig, x=10, y=25, zorder=100, which='metpy', size='small', **kwargs):

metpy/plots/tests/test_util.py

@@ -26,6 +26,16 @@ def test_add_timestamp():
     return fig
 
 
+@pytest.mark.mpl_image_compare(tolerance={'1.4': 9.51}.get(MPL_VERSION, 0.01),
+                               remove_text=True)
+def test_add_timestamp_high_contrast():
+    """Test adding a timestamp to an axes object."""
+    fig = plt.figure(figsize=(9, 9))
+    ax = plt.subplot(1, 1, 1)
+    add_timestamp(ax, time=datetime(2017, 1, 1), high_contrast=True)
+    return fig
+
+
 @pytest.mark.mpl_image_compare(tolerance={'1.4': 0.004}.get(MPL_VERSION, 0.01),
                                remove_text=True)
 def test_add_metpy_logo_small():