Basic support for filter effects is included in SVN trunk and in upcoming 0.45 release. At the moment only gaussian blur is implemented, so while specifications define a bunch of other effects and some other programs can handle them, Inkscape cannot render them yet. Also, tools for editing other types of filters do not exist yet.
Gaussian blur can be applied to an object by using Blur slider in Fill and stroke dialog.
In Inkscape preferences dialog there is a setting controlling the filter rendering quality. Even low quality often produces good enough rendering quality, but it takes a lot less time to render. When exporting an image from Inkscape, the best quality is always used, regardless of this setting.
Now that this one filter works, most of the basic framework needed for filtering exists.
These are the basic steps to create a new filter primitive:
- Write a new document model level class for this filter primitive (see src/sp-gaussian-blur.cpp)
- Write a renderer for this filter primitive (see src/display/nr-filter-gaussian.cpp)
- Add a pointer to a function returning an instance of the renderer class to function Filter::_create_constructor_table in file src/display/nr-filter.cpp
(this is likely not an exhaustive list)
Before new filter primitives can be useful, there has to be an user interface for applying them to shapes. A really good thing would also be an UI for creating filters out of filter primitives.