added transparent figure faq

jdh2358 · jdh2358 · commit c371027a0a65 · 2008-06-25T14:37:23.000Z
svn path=/trunk/matplotlib/; revision=5672
diff --git a/doc/faq/howto_faq.rst b/doc/faq/howto_faq.rst
@@ -6,6 +6,34 @@ Howto
 
 .. contents::
 
+.. _howto-transparent:
+
+How do I save transparent figures?
+==================================
+
+The :meth:`~matplotlib.pyplot.savefig` command has a keyword argument
+*transparent* which, if True, will make the figure and axes
+backgrounds transparent when saving, but will not affect the displayed
+image on the screen.  If you need finer grained control, eg you do not
+want full transparency or you to affect the screen displayed version
+as well, you can set the alpha properties directly.  The figure has a
+:class:`matplotlib.patches.Rectangle` instance called *figurePatch*
+and the axes has a Rectangle instance called *axesPatch*.  You can set
+any property on them directly (*facecolor*, *edgecolor*, *linewidth*,
+*linestyle*, *alpha*).  Eg::
+
+    fig = plt.figure()
+    fig.figurePatch.set_alpha(0.5)
+    ax = fig.add_subplot(111)
+    ax.axesPatch.set_alpha(0.5)
+
+If you need *all* the figure elements to be transparent, there is
+currently no global alpha setting, but you can set the alpha channel
+on individual elements, eg::
+
+   ax.plot(x, y, alpha=0.5)
+   ax.set_xlabel('volts', alpha=0.5)
+
 
 .. _howto-subplots-adjust:
 
