Filter effects is a part of SVG specification
NB: At the moment, Inkscape filter effects support is highly experimental
Filter effects are parsed from svg documents. A constant size gaussian blur is applied to objects that have filter-property set and it references to existing filter-element in the same document.
How to make it work
Preliminary filter effects support is now included in inkscape subversion reposistory.
There is no GUI to create filters or to attach them to objects. You have to do that with the XML editor in inkscape, for example.
- Edit -> XML Editor
- Select the svg:defs -element
- Click 'New element node'
- Type svg:filter as node type
- Change the id if you wish. I'll call the id 'xyzzy'
- Pick the object you wish to apply filtering to
- In XML editor, add new property for this object with name 'filter' and value of 'url(#xyzzy)'
Blur radius is read from inkscape configuration file, from attribute options.filtertest. See HandlingPreferences for info on how to add that attribute.