Tutorials:SWORD 103

The anatomy of an SWFilter

At the most basic level, a SWORD filter performs some distinct and concise transformation to the data stream.

The actual signature of a filter is very minimal, and looking at the SWFilter interface itself... http://crosswire.org/svn/sword/trunk/include/swfilter.h

... there is simply 1 method you need to implemented to create a filter:

char SWFilter::processText(
                SWBuf &text,
        const SWKey *key = 0,
        const SWModule *module = 0) = 0;

Basically, you're sent a buffer of text, possibly along with some context in the form of an SWKey and SWModule-- in case you care, and then you make some small change to the buffer.

Easy, right? Well, sortof.

Anyone can write a filter. The great thing about filters is that they partition up a very complicated task: processing a complex document, into tiny manageable chunks that anyone can tackle.

"Handle <title> tags in a buffer? Sure, I can do that! That's easy.... Wait.... What should I _DO_ with a <title> tag?"

That's when the real world hits and things get more complex. A SWORD filter is an easy to grasp, easy to code against, abstract concept.

How filters are orchestrated together inside the SWORD engine-- what distinct roles they are expected to fill, when, and in what order-- is hidden knowledge that for years only few have been privy to yield...

Stay tuned for "The Red Pill" coming soon to a listserv near you.