graphics context: use alpha value from foreground color if present

efiring · efiring · commit 4c078ddf68cc · 2011-08-16T21:50:54.000-10:00
When a Line2D color is given as an rgba, this causes the "a" part
to be used unless it is explicitly overriden by an alpha kwarg.
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -742,8 +742,7 @@ def get_linewidth(self):
 
     def get_rgb(self):
         """
-        returns a tuple of three floats from 0-1.  color can be a
-        MATLAB format string, a html hex color string, or a rgb tuple
+        returns a tuple of three or four floats from 0-1.
         """
         return self._rgb
 
@@ -771,9 +770,8 @@ def set_alpha(self, alpha):
         Set the alpha value used for blending - not supported on
         all backends
         """
-        if alpha is None:
-            alpha = 1.0
-        self._alpha = alpha
+        if alpha is not None:
+            self._alpha = alpha
 
     def set_antialiased(self, b):
         """
@@ -823,17 +821,19 @@ def set_dashes(self, dash_offset, dash_list):
     def set_foreground(self, fg, isRGB=False):
         """
         Set the foreground color.  fg can be a MATLAB format string, a
-        html hex color string, an rgb unit tuple, or a float between 0
+        html hex color string, an rgb or rgba unit tuple, or a float between 0
         and 1.  In the latter case, grayscale is used.
 
         The :class:`GraphicsContextBase` converts colors to rgb
-        internally.  If you know the color is rgb already, you can set
+        internally.  If you know the color is rgb or rgba already, you can set
         ``isRGB=True`` to avoid the performace hit of the conversion
         """
         if isRGB:
             self._rgb = fg
         else:
             self._rgb = colors.colorConverter.to_rgba(fg)
+        if len(self._rgb) == 4:
+            self._alpha = self._rgb[3]
 
     def set_graylevel(self, frac):
         """
