GTK Background Masking

[Tim Corio <tcorio rochester rr com>]

How can I mask out the background in a GdkPixbuf?

In my application I have loaded an image of a coin and have calculated
the location (X, Y, Radius) of the coin.  I want to draw a background
color everywhere outside of the circle.

Is there a way to draw a "filled arc" that is filled on the outside of
the arc?

Is there a way to draw my filled circle on a mask image then apply that
mask to my original image?

Thanks,
Tim