Add functions for setting a ternary specific background color

ternary/heatmapping.py

@@ -409,3 +409,12 @@ def svg_heatmap(data, scale, filename, vmax=None, vmin=None, style='h',
         output_file.write(svg_polygon(vertices, color))
 
     output_file.write('</svg>\n')
+
+
+def background_color(ax, color, scale, zorder=-1000, alpha=None):
+    """Draws a triangle behind the plot to serve as the background color."""
+    vertices = [(scale, 0, 0), (0, scale, 0), (0, 0, scale)]
+    vertices = map(project_point, vertices)
+    xs, ys = unzip(vertices)
+    poly = ax.fill(xs, ys, facecolor=color, edgecolor=color, zorder=zorder, alpha=alpha)
+    return poly

ternary/ternary_axes_subplot.py

@@ -2,6 +2,7 @@
 Wrapper class for all ternary plotting functions.
 """
 
+from collections import namedtuple
 from functools import partial
 
 import numpy
@@ -13,6 +14,9 @@
 from .helpers import project_point, convert_coordinates_sequence
 
 
+BackgroundParameters = namedtuple('BackgroundParameters', ['color', 'alpha', 'zorder'])
+
+
 def figure(ax=None, scale=None, permutation=None):
     """
     Wraps a Matplotlib AxesSubplot or generates a new one. Emulates matplotlib's
@@ -70,6 +74,11 @@ def __init__(self, ax=None, scale=None, permutation=None):
         # Container for the redrawing of labels
         self._to_remove = []
         self._connect_callbacks()
+        # Background
+        self._background_parameters = None
+        # Cache for the background triangle object, so it can be removed and redrawn as needed.
+        self._background_triangle = None
+        self.set_background_color(color="whitesmoke", zorder=-1000, alpha=0.75)
 
     def _connect_callbacks(self):
         """Connect resize matplotlib callbacks."""
@@ -454,3 +463,20 @@ def heatmapf(self, func, scale=None, cmap=None, boundary=True,
                              colorbar=colorbar, permutation=permutation,
                              vmin=vmin, vmax=vmax, cbarlabel=cbarlabel,
                              cb_kwargs=cb_kwargs)
+
+    def set_background_color(self, color="whitesmoke", zorder=-1000, alpha=0.75):
+        self._background_parameters = BackgroundParameters(color=color, alpha=alpha, zorder=zorder)
+        self._draw_background()
+
+    def _draw_background(self):
+        color, alpha, zorder = self._background_parameters
+        scale = self.get_scale()
+        ax = self.get_axes()
+
+        # Remove any existing background
+        if self._background_triangle:
+            print(self._background_triangle)
+            self._background_triangle.remove()
+
+        # Draw the background
+        self._background_triangle = heatmapping.background_color(ax, color, scale, alpha=alpha, zorder=zorder)[0]