Add masking for phase plots.

Author: matthewturk

yt/visualization/profile_plotter.py

@@ -1130,10 +1130,12 @@ def _setup_plots(self):
             else:
                 cmap = self._colormap_config[f]
 
+            masked_data = data.copy()
+            masked_data = np.ma.masked_array(data, ~self.profile.used)
             self.plots[f] = PhasePlotMPL(
                 self.profile.x,
                 self.profile.y,
-                data,
+                masked_data,
                 x_scale,
                 y_scale,
                 z_scale,