cartography - Polygon gradient fills / tint bands in QGIS

Is it possible to use a gradient fill on a polygon in QGIS?

I would like to have my polygons with a colour at the edges, fading to clear/white as it moves away from the edge. The majority of the centre of the polygon will be white or clear.

It is something people I know who use Illustrator can do. I wondered if there was a way to emulate it in QGIS.

Here is an example. I would like something like the purple shading.

Update:

This method suggested below does work, however it produces some annoying extra bits for my polygons. For example, see the image below:

I am unsure how to remove these. I cannot use a mask as I need to be able to see the base mapping and other data outside of this polygon on layers that are below this layer. Using a mask would obscure all of these layers.

I have included a link to Underdarks blog post about this, which gives more detail, and contains the code to set this up.

http://underdark.wordpress.com/2011/08/08/creating-a-gradient-fill-for-polygons-in-qgis/

Answer

There is no option for gradient fill as far as i know. But you can emulate a gradient if you don't mind some work creating your own symbol. I've done a quick example with only four color step, so it's not a smooth gradient ... but you get the idea.

All you have to do is create layers of type "simple line" and give them a positive offset. That will move the border "inside" the polygon. Don't forget to enable symbol levels for a clean rendering.